oil pumping and metering part of the petroleum proce

8/9/2019 Oil Pumping and Metering Part of the Petroleum Proce

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Petroleum Open Learning

Oil Pumping and Metering(Part of the Petroleum Processing Technology Series)

Contents

Section 1 - Centrifugal Pumps : Terms and Concepts..................................3Liquids, Gases and Fluids........................................................................................... !ass, Force and "eight............................................................................................. #ensity and Specific Gra$ity....................................................................................... %entrifugal Force........................................................................................................&'inetic nergy and Pressure nergy..........................................................................*ead Pressure........................................................................................................... .+Pressure....................................................................................................................-et Positi$e Suction *ead (P*)..............................................................................%a$itation................................................................................................................../Flo0 $ #ifferential Pressure......................................................................................

Section 2 – Construction and Operation of Centrifugal Pumps.................161mpeller Speed..........................................................................................................23earings..................................................................................................................../-Seals........................................................................................................................./Pump %onfigurations................................................................................................/%entrifugal Pump Performance %ur$es...................................................................../4 5 %entrifugal Pump 5rrangement............................................................................../

Section 3 – Oil Metering and Sampling........................................................31Tur6ine !eters....................................................................................................... ...&!etering Systems.....................................................................................................7

Sampling Sstems.........................................................................................!1

Section ! – Pig "aunc#ing $acilities............................................................!2Pig Launchers.......................................................................................................... .44

Section %- & Tpical Oil Pumping and Metering Sstem.........................!'

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Training Targets

"hen you ha$e completed this unit on Oil Pumping and !etering, you 0ill 6e a6le to

• 8plain some of lie technical terms and concepts 0hich lie 6ehind the operation of a centrifugal pump /• List component pails of a centrifugal pump /• 8plain the operating principle9 of a centrifugal pump /• #escri6e the construction and operation of tur6ine and differential pressure !eters /• 8plain the function and operation of a typical meter run

/• #escri6e the procedure for pro$ing a meter /• List the essential element of an ail sampling system /• #etail the main features of a pig launching oysters, and its method of operation /• #escri6e a typical layout for the ail handling (or oil pumping and metering) section of a production facility /

Tic: the 6o8 0hen you ha$e met each target

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Oil Pumping and MeteringSection 1 - Centrifugal Pumps : Terms and Concepts

1n this first section, 0e 0ill loo: 6riefly at a num6er of concepts 0hich

relate to the operation of centrifugal pumps. 1 0ill also e8plain some ofthe terms often used 0hen 0e are discussing ho0 these concepts can6e applied in practice.Throughout this unit 0e 0ill 6e concentrating on centrifugal pumps6ecause these are the most common ones used in oil pumping andmetering ser$ices.

"i(uids) *ases and $luids

3oth liquids and gases are called fluids 6ecause each has the

a6ility to flo0.

1n this unit 0e 0ill use the term fluid 0hen descri6ing something0hich can happen to a gas or a liquid. "hen 0e need to ma:e adistinction, 1 0ill use the specific term liquid or gas.

Mass) $orce and +eig#t

The mass of an o6;ect is a measure of the quantity of matter

present. This o6;ect may ha$e $arious forces acting on it, the mostimportant of 0hich is li:ely to 6e the force of gra$ity.


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5 ga ll on of 0a te r has a ma ss of - po un ds .

5 ga llon of gasoline has a mass of 7.s pounds.

5 gallon of salt 0ater 6rine has a mass of 1 f pounds.

"hat are the specific gra$ities of gasoline and 6rine B


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Centrifugal $orce

*a$e a loo: at Figure /.

1t sho0s a spinning dis:. 1f 0e let a drop of 0ater fall onto the face ofthe dis:, near to the centre spot, it 0ill follo0 the type of path sho0n.This is 6ecause the drop is affected 6y t0o forces during its tra$elC

centrifugal force, 0hich tends to thro0 the droplet out0ards, causingit to speed up as it approaches the edge of the dis:friction, 0hich 0ill cause the dis: to attempt to drag the droplet round0ith it as it rotates.

The relati$e siDe of these t0o forces 0ill determine the angle at 0hichthe droplet lea$es the dis: edge.

This angle is important, as you 0ill see 0hen 0e come to the sectionon %onstruction and Operation of %entrifugal Pumps (Section /). Thedesign features of the pump encourage a flo0 path for the liquid 6eing

pumped, 0hich is $ery similar to the droplet tra;ectory in Figure /.

This ensures that the pump imparts the ma8imum amount of energy tothe liquid. 1n this case, energ of motion, or inetic energ istransferred.

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inetic 4nerg

"e ha$e seen that :inet ic energy is energy of motion, or mo$ement.The amount of :inetic energy possessed 6y any mo$ing o6;ectdepends upon .

1ts mass (E0eight)

its $elocity (?speed?)

1n mathematical terms, :inetic energy (') can 6e calculated 6y usinga formula' >AH mass 8 $elocity>

1f the mass is e8pressed in :ilograms and the $elocity in metres persecond, the :inetic energy 0ill 6e in 5oules.

To confirm your understanding of this relationship try the follo0ing Test ourself .

Test ourself 2

5 small car has a m ass of --- :ilograms and istra$elling at +- :ilometres per hour,

5 large t ruc: has a m ass of /- --- :ilograms, and istra$elling at 2- :ilometres per hour,

"hich one has the greater :inetic energy B


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inetic 4nerg and Pressure 4nerg

$igure 3 illustrates the flo0 of a fluid across a restriction, and ho0 the fluid $elocity and pressure$ary during this process.

Figure C Flo0 5cross a Iestriction

Let us go into a little more detail on these pressure and $elocity changes 6y considering si8separate paints in the processC

point &C fluid is flo0ing along the pipe at asteady speed and .almost constant pressure.


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8ead Pressure

The term #ead pressure or #ead is often usedin the oil and gas industry, especially 0henreferring to pumps. 1t is the pressurede$eloped 6y a head, or column height, ofliquid.

1n the paragraph entitled ?Pressure?, 0e sa0that the head pressure applied 6y one footdepth of 0ater 0ill 6e -.4 psi. For - feet of0ater the head pressure 0ould 6e 4. psi9 for-- feet, 4. psi, and so on.

o0 let us com6ine 0hat 0e :no0 a6outspecific gra$ity and head pressure. Try thefollo0ing Test ourself to com6ine these t0ofactors together

"e ha$e already sho0n that centrifugal forcecan impart :inetic energy to a su6stance as aresult of a spinning action. "e ha$e also seen

that :inetic energy can 6e con$erted intopressure energy.

%entrifugal pumps are dynamic pumps 0hich,primarily, impart :inetic energy to the f luid 6eingpumped. They do not create pressure directly.

Pressure results from the liquid slo0ing do0n,and the :inetic energy con$erting to pressureenergy.

The pressure de$eloped 0ill depend on thedensity of fluid 6eing pumped.

5 centrifugal pump, 0or:ing at a fi8ed flo0rate,0ill generate the same height of head, 6ut 0illgenerate a lo0er head pressure, 0hen pumpinggasoline, than 0hen 0ater is 6eing pumped,

6ecause 0ater is hea$ier than gasoline.

The different categories of head pressurereferred to in pumping operations are sho0n inFigure & on the ne8t page.

Test ourself 3

The specific gra$ity of gasoline is -.+&,and that for a particular salt 0ater is ..

"hat 0ill 6e the head pressurede$eloped 6y - feet of the gasoline,and 7 feet of this 6rine B

The ans0ers to this Test


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The suction #ead represents the headpressure present at the pump suction.

The disc#arge #ead represents the headpressure deli$ered 6y the pump.

The total #ead (0hich is the difference6et0een suction and discharge heads)represents the additional pressureimparted to the liquid 6y the pump


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o0 let me introduce you to anotherprinciple of science = Conseration of4nerg.

This tells us that t#e total energ contentof a sstem 9ill al9as remain constant.

1f the :inetic energy content of our systemincreases then, to compensate for this,some other form of energy possessed 6ythe system must decrease. This other formof energy is pressure energ. Figure sho0s that, as the $elocity (:inetic energy)increases, the pressure (pressure energy)decreases.

point C C this is a ne0 steady state. The

fluid has a higher $elocity and a lo0erpressure 6ut 6oth of them are steady as thefluid passes across the restriction.

points , and 4 re$erse the changes 0hichoccurred at points 5 and 3.

1t is 0orth noting that, across the processo$erall, a small reduction of pressure hasoccurred. #ue to tur6ulence in the system,some pressure energy has 6een con$ertedinto heat energy.


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et Positie Suction 8ead P8/

1 0ould li:e you to thin: a6out t0o commonsituations in 0hich you ha$e seen 6u66lescoming out of a liquid.

. 1f you heat up a perB - 0ater, t0o thingshappenC

long 6efore the 0ater 6oils, 6u66les are

seen rising through the liquid asdissol$ed air comes out of solution0hen the temperature 6egin9 to increase

at the 6oiling point, the liquid 6u66les

$igorously as the 0ater is rapidly

con$erted into steam

"ater at sea le$el 6oils at --K% (//KF). 1 amsure you 0ill ha$e heard, ho0e$er, that the6oiling point of 0ater (or any other liquid) asyou clim6 from sea le$el, so that it can 6edifficult to coo: an egg properly on top of a highmountain. This is 6ecause atmosphericpressure falls the higher up 0e get.

/. 1f you open a 6ottle lemonade, 6u66les areseen rising through the liquid as dissol$ed

gas comes out of solution 0hen thepressure is released (reduced).

1f these effects are o6ser$ed in 0ater andlemonade, it is roil to assume that they 0illhappen in other liquids as 0ell. So let usno0 $isualise ho0 these effects caninfluence the operation of a pump.

"e already :no0 that fluids can only flo0 fromareas of high pressure to areas of lo0 pressure.Suppose that the liquid 6eing pumped entersan area of lo0 pressure. ThenC

1f the liquid 0as near its 6oiling point, the

pressure drop may cause the liquid to 6oiland release gas or $apour

if the liquid 0as near to the pressure at

0hich dissol$ed gases are released, thepressure drop may cause these gases tocome out of solution

1n either case 0e can predict that, if thepressure is increased again, the releasedgases 0ill go 6ac: into the liquid, either6ecause 6oiling stops or the released gases re=dissol$e.

"hen a centrifugal pump is running, a lo0pressure area is created at the suction. Thisencourages liquid further upstream to flo0 intothe pump suction.

The accompanying drop in pressure may cause

gas or $apour to 6e released for either of thereasons descri6ed a6o$e. 1t is important that0e pre$ent this happening, for reasons that 10ill e8plain a little later under E%a$itation.

"e must therefore always ha$e sufficientpressure at the pump suction to pre$ent gas or$apour release for 0hate$er reason. The

minimum pressure necessary to do this iscalled the net positie suction #ead PS8/.

5 further pressure reading 0hich is rele$ant tothe suction end of the pump is called the staticsuction line pressure. 5s the name implies,

this is the measured pressure at the pumpsuction 0hen pumping has stopped.

"e no0 ha$e three pressure $alues 0hichrelate to the pump suctionC

a) the pressure at 0hich gas or $apour isreleased

6) the static suction line pressurec) the PS*


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5 pump manufacturer 0ill specify the PS*and ma8imum operating temperaturerequired for each pump to handle a gi$enliquid effecti$ely. The PS* should 6emaintained o$er the entire range of thepump.

To 6e safe, most pumps 0ill 6e operated ;usta6o$e their PS*. 5n adequate safetymargin for most applications 0ould 6e feet,or -, head of 0ater pressure a6o$e thePS* specified 6y the manufacturer(0hiche$er is the larger).

1n general, the industry standard is to 0or: interms of ?head of 0ater?. This is 6ecausee$eryone :no0s the density of 0ater andpumps can easily 6e tested to ma:e surethat they produce the le$el of head specified.

Caitation

"e ha$e discussed at some length theimportance of PS* and other factors inpre$enting the release of gas or $apour

6u66les in the suction of the pump. "e 0illno0 loo: at 0hy it is so important to pre$entthis.

1f gas is released at this point in the system,it 0ill gi$e rise to an effect :no0n ascaitation.

The formation of 6u66les is, in itself, quiteharmless. *o0e$er, as the liquid containingthese gas 6u66les, or ca$ities, passesthrough the pump, the pressure 0ill rise. o0

0e already :no0 that, if gas is released froma liquid for the reasons 1 ha$e descri6ed, anincrease in pressure 0ill dri$e this gas 6ac:into the liquid again.

5s these tiny ca$ities created in the liquidcollapse, the liquid tends to rush in from all

angles to fill the ca$ity. The ca$ity is said toimplode.

This inrushing liquid can transmit $ery largeforces. "hen the 6u66les are near a metallicsurface, these forces are applied directly tothe solid surface. "hen a pump iscaitating, this process is 6eing repeatedmany thousands of times each second andthe effect results in noise, $i6ration ande$entual erosion of metal from the surfaces.1n $ery se$ere cases, for e8ample 0here thepump is handling liquids carrying small solidparticles, the impeller can 6e eroded in arelati$ely short space of time.

5n equally important factor is that se$ereca$itation can result in a failure of the pump

to deli$er flo0 at the e8pected head.

"hen pumping oil, the drop in head andefficiency is not quite so se$ere as 0ith 0ater 6ecause the liquid is composed of mi8turesof different hydrocar6on compounds. The6u66les 0hich appear 0ill consist of lighterhydrocar6ons such as methane or ethane.These can 6e more easily rea6sor6ed as thepressure is increased. "hen pumping 0aterthe 6u66les are nearly al0ays caused 6y the0ater 6oiling at a reduced pressure. 1n this

situation the 6u66les collapse $iolently andeach implosion is of a high intensity.

Test ourself !

5s a chec: on 0hether you ha$eunderstood 0hat 1 ha$e 6een sayinga6out pressures at the suction end of thepump, list these three pressure $aluesC

a) the pressure at 0hich gas or$apour is released

6) the static suction line pressurec) the PS*

1n order of decreasing pressure, andsee if you can e8plain the reasons foryour ans0ers.


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$lo9 ,ifferential Pressure

Ta:e another loo: at Figure .


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This sho0s the relationship 6et0een flo9 anddifferential pressure, 6oth e8pressed as apercentage of the ma8imum possi6le underthose particular circumstances.

"e can see, for e8ample, that &- of thema8imum flo0 is equi$alent to /& of thema8imum differential pressure.

o0 let us suppose that, in our pipeline, 0ecan generate up to &- psi of pressure at theinlet and deli$er up to &- gallons of liquid perminute. Let us also suppose that, at the outlet,the liquid discharges into a pond at - psi.

"e therefore ha$e a differential pressure of -=

&- psi and a flo0 rate of -=&- galsAmin. Let usloo: at the conditions under different flo0s andpressures.

if 0e regulate the inlet flo0 to & galsAmin(- of ma8imum) 0e could e8pect $erylittle tur6ulence. From Figure 7 0e canestimate that the differential pressure 0ill6e of ma8imum, or -.& psi, at this flo0rate.

if the flo0 is increased to - galsAmin (/-

of ma8imum), 6oth tur6ulence and thepressure drop 0ill increase. 5t a /- f lo0rate, the differential pressure 0ill rise to4 of ma8imum, or /.- psi.

(


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1n this section, 0e ha$e loo:ed at some of the scientific terms andconcepts 0hich help us to understand the design and operation ofcentrifugal pumps.


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Oil Pumping and MeteringSection 2 – Construction and Operation of Centrifugal Pumps

The centrifugal pump is the commonest form of pump in use today. 1t isrelati$ely cheap, easy to maintain and is to 6e found almost e$ery0here0hen large flo0s are required.

"e 0ill first ta:e a loo: at the 6asic configuration of a centrifugal pumpand then at the component parts, to see 0hat they do and ho0 they 0or:.

The type of pump illustrated in Figure is one of the simplest. 1t consistsof• a casing, 0hich contains and supports the rest of the pump

components. 5ccess to the inside of the pump is $ia a $ertical split at

the 6ac: of the casing (not sho0n)

• a suction flange, 0hich directs the liquid entering the pump casing intothe impeller

• an impeller, 0hich imparts :inetic energy to the liquid

• a pump shaft, connected through a coupling to a motor 0hich dri$esthe shaft and the attached impeller(s)

• a 6earing housing, 0hich supports the shaft

• a shaft seal, 0hich pre$ents liquid escaping from the casing along theshaft

• a discharge flange, 0hich directs the liquid a0ay from the pump

Figure C 5 Typical %entrifugal Pump

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$igure ' sho0s a cross section through a single impeller pump, illustratingthree more :ey items of equipmentC

• The 9ear rings, 0hich act as seals 6et0een the high pressuredischarge side and the lo0 pressure suction side of the impeller

• The 0ear rings are so called 6ecause they 0ear in preference to theimpeller. They are Nslee$ed> on to the impeller, and may 6e replaced0hen 0orn

• The ;alance #oles, 0hich allo0 the pac:ing to operate at suctionpressure rather than discharge pressure. This reduces the differentialpressure across the pac:er and impeller, and therefore reduces the?thrust? forces

• The pacing, 0hich pre$ents liquid escaping from the casing

"e 0ill no0 e8amine some of these components in more detail.

Figure + C %ross Section Through a Single 1mpeller Pump


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sho0s the t0o main types of casing0hich allo0 this to happen 0ithin the pump.

The upper diagram sho0s a olute casing. 1n this type of pump, theliquid lea$es the tip of the impeller, and is thro0n into a channel 0ith anincreasing area of cross=section. *ere the liquid slo0s do0n and :ineticenergy . is con$erted into pressure energy.

The $olute design ensures that it is aligned 0ith the tra;ectory of the liquidlea$ing the impeller. This ensures efficient energy transfer andcon$ersion.

The liquid is then guided to0ards the pump discharge flange.

The $olute type of pump is the most common type in use.

The lo0er diagram sho0s a diffuser casing. 1n this type of pump, as theliquid lea$es the tip of the impeller it mo$es through a set of angled $anes:no0n as diffusers. 5gain, these are lined up 0ith the direction of thepumped liquid as it lea$es the impeller. The diffusers then guide the liquidinto the outer section of casing 0here its $elocity decreases and pressureincreases 6efore flo0ing to the discharge flange.discharge flange

Pump discharge flange

S1GL @OL %5S1G

Figure - C @olute and #iffuser %asings


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7earings

$igure 11 is an illustration of a simple 6earingarrangement. The shaft is supported 6y t0oradial 6all 6earing races, 0hich allo0 it torotate 0ith minimum friction.

T#rust force is a force 0hich is directed alongthe a8is of the pump shaft. 1t arises 6ecause of

the difference in pressure 6et0een thedischarge and suction sides of the pumpacting on the impeller. 1n Figure , the thrustforce 0ill 6e from right to left, (from highpressure to lo0 pressure).

1n this case, to counteract the thrust force, a6all 6earing race (the t#rust ;earing) ismounted 6et0een t0o $ertical plates. 1t allo0sthe shaft to turn 0ith a minimum of friction as itta:es up this thrust force.

The slinger rings (also called flinger rings)are t0o slender rings, often of 6rass, 0hichslide up and do0n the shaft as it rotates. Theslinger rings dip into the lu6ricating oil and, asthey turn, transfer oil onto the shaft. The oilthen runs along the shaft and contacts thefaces of the 6earings. %entrifugal force thro0sthe oil out0ards along the 6earing faces tolu6ricate and cool them.

The oil in this type of 6earing is either topped

up through an oil fill plug, as sho0n, or isautomatically replenished $ia an oil 6ottlearrangement.

oil fill plug

sump drain plug oil sump

Figure C 5 Typical 3earing 5rrangement

!otor


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Figure / C 5 Typical Pac:ed Seal


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The shaft enters the pump casing from theright hand side of the diagram and passesthrough a stationar seal . The stationaryseal is fi8ed to the pump casing and does notrotate.

5ttached - the Shaft is a rotar (of rotating)seal. Lea:age along the length of a shaftpre$ented 6y >O> rings 0hich seal the gap6et0een shaft and rotating seal. The >-> rings

turn together 0ith the shaft and rotating seal.

The sealing faces of the rotating andstationary seals are usually of machinedcar6on or high grade stainless steel 0hichare polished to a mirror finish. The t0ofaces are held $ery closely together 6y aspring and 6y the pressure of the liquid inthe pump.

5 small amount of the liquid 6eing pumped is

often ta:en form the discharge of the pump,filtered, and then returned through themechanical seal $ia the seal flus# inlet. Thisliquid helps to :eep the mechanical seal clean,cool and lu6ricated.

dri$e end

Stationary seal

Figure C 5 Typical !echanical Seal


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Pump Configurations$igure 1! sho0s e8amples of ho0 centrifugal pumps may 6e configured to increase flo0, or toincrease pressure.

Figure 4 a, 6 and cC%entrifugal Pump %onfigurations

n Figure 4a, a single pump is deli$ering --gallons per minute 0ith a total head of &- psidischarge head = suction head total head.

Figure 46 sho0s that, to increase the flo0,t0o pumps arranged in parallel are needed =that is, the pumps ha$e a common suction anda common discharge.

1n this case, 0e can

b)

c)


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• run either pump on its o0n to produce a flo0 rate of -- gallons per minute and a total head of &-psi, or,

• run 6oth pumps together to produce a flo0 rate of /-- gallons per minute and a total head of &-psi.

1n Figure 4c, 0e can increase the pressure 6y running t0o pumps in series. This means that the firstpump discharges into the suction of the second pump.

1n this case• 6oth pumps must 6e run together

• the com6ination of 6oth pumps 0illproduce a flo0 rate of -- gallons perminute and a total head of -- psi.

1n most instances 0here high pressures arerequired, it is easier to mount a num6er ofimpellers on a single shaft. These pumps are

called multi-stage pumps. They gi$e us highflo0 rates, and a gradual pressure rise o$er asmany stages as required. Some main oil Figure4 a, 6 and c Cpipeline pumps may ha$e morethan eight impeller stages.


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Centrifugal Pump PerformanceCures

$ery centrifugal pump is designed andmanufactured for a specific purpose. Thispurpose is summarised in a pumpperformance cure.

Figure & sho0s a typical performancecur$e 0hich gi$es us the follo0ing detailsa6out a specific pumpC

• on the left hand side of the cur$e 0hichgi$es us the follo0ing details a6out aspecific pump

) efficienc - from -=--. Thiscompares the po0er the pump is using

to the 0or: it is achie$ing

/) po9er = from -=/4 :ilo0atts in this case.This indicates the amount of po0er themotor is consuming

) total #ead = this indicates the pressure0hich the pump can achie$e

on the top right hand side of the chart 0ecan see the required PS8 (net positi$esuction head) in metres of li(uid. (you 0ill

recall that PS* 0as descri6ed in Section on Page )


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• the horiDontal a8is of the chart gi$es flo9rate in cu6ic metres per hour.

• in the 6ody of the chart 0e find cur$es 0hichsho0 the relationship 6et0een

) PS* and flo0rate/) efficiency and flo0rate

) po0er and flo0rate4) total head and flo0rate

Ta:e a fe0 minutes to study Figure & and thentry Test ourself 6 and ?.

The ans0ers to these can 6e found in C#ec ourself 6 and ? on Pages 77 and 7


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o0, to summarise 0hat 0e ha$e co$ered sofar in Section /, try Test ourself ':

%hec: your ans0ers in %hec:


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& Centrifugal Pump &rrangement

3efore 0e loo: at a typical oil pumping system, let us thin: a6out those items of equipment 0hich youare most li:ely to come across.

Figure 7 is an illustration of a typical centrifugal pumping arrangement.

Figure 7 C 5 Typical %entrifugal Pump 5rrangement


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The motor 0hich dri$es the pump is called themain drier . 1n this case, the main dri$er is anelectric motor, 6ut for 6igger pumps it may 6ea gas tur6ine or a diesel engine.

The motor has a set of local s9itc#es forstarting and stopping. 1n some cases a localammeter is fitted to chec: 0hether the motoris running properly. 1n many instances, the

pump motor may also 6e started from aremote location, such as a control room, either manually or $ia an automatic start system.

The motor shaft is lin:ed to the pump shaft $iaa coupling, designed to transmit po0er fromthe motor to the pump, and to ta:e care of anysmall shaft misalignments 0hich may occur.

The flo0 of liquid into the pump is through asuction ;loc ale, 0hich can 6e used toisolate the pump from the upstream process if

required. Occasionally, a strainer or filter (notsho0n) may 6e fitted to the suction line,do0nstream of the suction 6loc: $al$e, topre$ent de6ris from entering the pump.

The pump casing is fitted 0ithC

• a casing ent $al$e, used to 6leed off anygas or air in the pump 6efore starting

• a casing drain $al$e, used to drain liquid

from the pump after shutdo0n

The discharge of the pump is fitted 0ithC

• a disc#arge pressure gauge, 0hichindicates the pressure produced 6y thepump

• a disc#arge c#ec ale, 0hich onlyallo0s flo0 in one direction, a0ay from thepump. This $al$e, therefore, pre$ents liquidflo0ing 6ac: through the pump, 6ac:=spinning it and causing damage to theseals and 6earings of 6oth pump andmotor

• a disc#arge ;loc ale, 0hich can 6eused to isolate the pump from thedo0nstream process, if required

Minimum $lo9 Sstem

5ll centrifugal pumps require one other item ofequipment for their protection.

1f 0e loo: 6ac: at the performance cur$e inFigure & 0e can see that, 0hen the pump isrunning at Dero flo0, it is still using a6out 4:ilo0atts of po0er. "e also :no0, from theperformance cur$e, that the pump efficiency0ill ha$e fallen to Dero.

So, 0hat has happened to the po0er 0e areusing B

The ans0er, of course, is that it is con$ertedinto #eat energ.

There 0ould 6e great tur6ulence inside apump 0ith the impeller turning through liquidtrapped 0ithin the pump. The temperature0ould rise, increasing the chances ofca$itation.

1n some instances, 0ith large and po0erfulpumps, damage can then occur in a matter ofseconds. 1n smaller machines it may ta:emuch longer = 6ut damage 0ill e$entuallyoccur.

To pre$ent this situation from happening, aminimum flo0 must 6e esta6lished andmaintained through the pump at all times 0hile

running. This minimum flo0 le$el is specified6y the pump manufacturer.

5ll centrifugal pumps 0hich are at ris: can 6efitted 0ith a minimum flo9 sstem. Thisensures that, 0hile the pump is running, thereis sufficient liquid flo0 to ensure that nodamage occurs.

1n some instances, the minimum flo0 systemconsists of a simple orifice plate, siDed for thecorrect flo0. The plate is inserted into a line

through 0hich is re=cycled a fi8ed flo0 frompump discharge to pump suction at all t imes.

1n other instances a flo0 measuring de$ice isfitted into the suction of the pump. This de$icecontrols a flo0 control $al$e, inserted into aline 0hich re=cycles a fi8ed amount of flo0. 1fthe flo0 falls 6elo0 the pre=set minimum le$el,the flo0 control $al$e 0ill open to restore flo0rate to the minimum.


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5 simple and $ery common de$ ice is ill ust rated in


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Summary of Section /

Shaft seals

"e e8arnined Finally 0e loo:ed at 0ly cenlr*ugal pumps are fitted 0ith a mintmum 1le0 &qstern, oriSuring thatflo0 difterent types of pump casing played a they do not 6ecome damaged due to o$erheating part in con$erting :ir8atic energy into pressure and ca$il!ion.energyho0 e can change flo0 andar prassura

characteris,tfcs 6y changirG pump 1n the ne8t s2olian. "e "ill ta>r.%Q 9 1Ci=R: at a typic;OceniiguCalions (parallel $. series) aid metering land sampling systern1n particular, 0e loo:ed atthe construction and Cinierp=re9etion of a set of pump performance cur$es for a typical centrifugal pump and ho0 they incorporate the concepts and ideas 0hich0e had pre$iously enc,ountereda typicat centriluga> pump arrangement 0ith its inlet and outtlet lines and associated equipment


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Oil Pumping and MeteringSection 3 – Oil Metering and Sampling

"e ha$e considered the 6asic design andoperation of a centrifugal pump.

o0 it is time to ta:e a loo: at crude oil

metering, metering sstems, and samplingtec#ni(ues.

There are four main reasons for metering andsampling a flo0 of crude oil

) to measure the amount of hydrocar6onsremo$ed from the reser$oir. This allo0sfield production plans to 6e updated andre$ised.

/) to determine the amount of eachcomponent in a mi8ed oil stream. This isparticularly important 0here the productionfrom separate oil fields are mi8ed (perhapsas part of pipeline sharing agreements)prior to the point of sale.

) to measure the product for ta8 purposes.This is called fiscal metering.

4) to ensure that no loss of product hasoccurred. 1n an offshore oilfield, the amountof metered offshore product, plus anylosses or gains due to pac:ing orunpac:ing of the pipeline (see 6elo0), iscompared regularly 0ith the amount ofonshore metered product.

!ulti=component liquids such as crude oilare slightly compressi6le. 1ncreases ordecreases in the o$erall pipeline pressure0ill produce small changes in the $olume of

oil contained 0ithin the pipeline. The termspacing and unpacing are used todescri6e these small changes in $olume. 1fthey are ignored, apparent losses or gainsin the pipeline in$entory can accumulate.

The sampling and metering sstem is placedas late in the oil handling sequence aspossi6le. There are a num6er of reasons forthisC

• it should 6e do0nstream of any ;oosterpump 0hich is fitted. (On manyinstallations, the crude oil passes through a6ooster pump to raise the pressure prior toentering the metering and sampling section.This ensures that no gas or $apour 0ill6rea: out of the liquid 0hilst it is 6eingmetered and sampled)

• no further processing of the fluid occurs6efore e8port, and the fluid sampled and

metered is representati$e of the fluid 6einge8ported

• metering ta:es place do0nstream of 0aterremo$al. 5t a 0ater content higher thana6out , serious discrepancies occur inmeter accuracy 0hich conflict 0ith theo6;ecti$es of metering and sampling

The process of metering and sampling istherefore gi$en a $ery high priority. !etersthemsel$es are chec:ed regularly, using apermanently installed meter proer . The meter

pro$er itself is chec:ed regularly to ensure thatit, too, is accurate.

To emphasise this point, try Test


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There are many methods used to measurefluid flo0. 1t is 0orth noting, ho0e$er, that mostflo0 rates are arri$ed at indirectly 6y measuringsome other property of the flo0ing fluid, andthen relating the $alue of this property to flo0rate 6y some form of cali;ration. This is truefor the t0o most common de$ices used for

metering produced oilC

• the differential pressure meter • the tur6ine meter

For e8ample, as you 0ill see later on

• in the differential pressure meter, it is apressure difference 0hich is measureddirectly

• in the tur6ine meter, 0e measure thefrequency of electrical pulses

1n this nit, 0e 0ill ta:e a 6rief loo: at thedifferential pressure meter, and ho0 itoperates. "e 0ill then consider the tur6inemeter.

,ifferential Pressure Meters

#ifferential pressure metering is one of the

oldest methods of measuring flo0rates. 1t issimple, accurate, relia6le and relati$elyine8pensi$e. 1t 0ill record $olume flo0rates(say, cu6ic meters per day), 6ut mass flo0rates

(say, tonnes per day) can 6e calculated if thedensity of the oil is :no0n.

The most common differential pressure de$iceis one 0hich uses a restriction, usually anorifice plate, in the pipeline. The pressure dropacross this restriction is measured. This

pressure differential can then 6e related toflo0rate 6y the use of, for e8ample, cali6rationta6les or graphs. 5 large amount of cali6rationdata has 6een pu6lished on this.

The orifice plate is popular 6ecause it has nomo$ing parts and is $ery accurate if cali6ratedand maintained correctly.

1n order to measure the pressure drop, thereshould 6e pressure tappings on either side ofthe orifice plate, as sho0n in $igure 1'.

These are usually locatedC

• one pipe diameter upstream of the orifice

plate and a half diameter do0nstream

or

• in the flanges 0hich hold the orifice platein the pipeline


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The first method pro$ides more accuracy, 6utthe second method is most 0idely used.

1n general, accurate metering can only 6eachie$ed 0hen the orifice plate is designed,fa6ricated and installed 0ith great care.

The most common type is the s(uare-edgeorifice plate, sho0n in Figure +.

"e must ensure that the flo0 entering thede$ice is steady and free of eddies 0hich0ould affect the accuracy of the meter. Theorifice plate should, therefore, 6e placed at apoint 0here temperature and pressure areconstant. 1n addition, 6ends, $al$es and otherfittings upstream of the orifice plate tend todistur6 the flo0 pattern of the fluidapproaching the plate. To a$oid this, it is

common practice to specifyC

• a minimum length of straight pipe 6othupstream and do0nstream of the orificeplate

or

• a flo9 straig#tening ane to 6e fittedupstream of the plate

5 flo0 straightening $ane is a length of pipe0ith a set of fins running along the inside. 5sthe fluid flo0s along this stretch of pipe, thefins straighten the flo0 and pre$ent s0irling.Flo0 straightening $anes are also usedupstream of tur6ine meters.

$igure 1=, demonstrates ho0 the pressurechanges as fluid passes through an orificeplate. The differential pressure is measured6et0een points P and P/. Point P/ ispositioned in line 0ith the ena contracta =the point at 0hich fluid $elocity is at itshighest, and pressure at its lo0est.

The differential pressure thus created 0illdepend mainly upon

• type of fluid• pipe diameter • orifice diameter • flo0 rate• inlet pressure

The differential pressure thus recorded maythen 6e con$erted into a flo0rate figure.


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Figure 2 C Pressure %hanges 5cross anOrifice Plate


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Tur;ine Meters

Tur6ine meters are the most popular method of measuring produced oil. They are accurate,relia6le and are easily pro$ed and ad;usted.

Tur6ine meters consist of a straight flo0 tu6e0ithin 0hich a tur6ine or fan is free to rotate.. The flo0ing

stream causes the tur6ine to rotate at a speedproportional to the flo0rate. 1f the flo0increases, the tur6ine 0ill spin faster. 1f the flo0decreases the tur6ine 0ill rotate more slo0ly.

1n most units, a magnetic pic:=up systemsenses the rotation of the tur6ine rotor. 5s each6lade passes the pic:=up coil, an electric pulseis generated. ach pulse is counted and, aseach pulse represents a :no0n $olume ofliquid, the total flo0 of oil can 6e calculated. 1nsome cases, t0o pic:=up coils are installed, so

that the t0o separate pulse counts may 6ecompared 0ith each other as an additionalchec:.

Figure /- C Tur6ine !eter

One of the ma;or ad$antages of a tur6ine meter is in its use for producing additional flo0 data.The electrical pulses generated can 6e fed intoa computer system, 0hich can then performother, more comple8, flo0 calculations. Thisadditional information may 6e added to the f inalread=out.

1t should al0ays 6e remem6ered that theaccuracy of a tur6ine meter depends almostentirely on the precision of the rotor and ho0consistently its speed of rotation can 6e relatedto flo0. 1f the rotor 6ecomes damaged, 0orn ordirty, then its capacity to measure flo0accurately 0ill suffer dramatically.


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Metering Sstems

The component parts of a typical tur6inemetering run are sho0n in $igure 21. Theseconsist of

• 5 manually operated


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Figure / C !eter Stream %omponents


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5 flo9 control ale, 0hich controls the flo0of liquid through the metering run. "hen thereare t0o or more metering runs, a centralmetering controller 0ill apportion flo06et0een the different flo0 control $al$es toensure that each meter run is operating 0ithinits limits.

5 motor operated outlet ;loc and ;leedale (!O@), 0hich allo0s the metering run to6e positi$ely isolated from the rest of theprocess do0nstream. This isolation is required0hen the meter run is out of ser$ice, or 0hen itis 6eing proed 6y the meter pro$ing system.

5 second, motor operated ;loc and ;leedale (!O@), 0hich is opened 0hen the meterrun is 6eing pro$ed. "hen this occurs the flo0

is di$erted through the second !O@ to themeter pro$ing system.

1n practice, the pressure, temperature anddensity of the oil may change 0hile the flo0rateis 6eing measured. To compensate for thesechanges, readings of the temperature,pressure and density are ta:en. Thisinformation is then fed, together 0ith data fromthe flo0 measurement de$ice, into the flo0computer. %orrected $alues for $olume flo0rate, mass flo0 rate, etc., can then 6e

computed and recorded.

Therefore, in many meter runs, 6ut not sho0nin Figure /, you 0ill find

• a thermometer, 0hich measures thetemperature of the stream 6eing metered

• a pressure transmitter

• an on=line densitometer

Meter Proing


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Pipe pro$ers usually consist of a =shapedor "=shaped length of pipe. $igure 22 is anillustration of a ;i-directional @-s#apedmeter proer loop.

Figure // C 5 3i=#irectional Pro$er Loop



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Figure /C Pig #esigns

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3rush pig

3rushes

sphere

Foam 3rush pig



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& ;i-directional @-s#aped meter proerloop, operates as follo0s9

The flo0 enters the meter pro$er through themeter under test.

1n the position sho0n, the oil flo0 is holding thecali6ration sphere against the 6uffer. 1f the 4=0ay di$erter $al$e is no0 turned through 2-degrees, the flo0 through the pro$er loop isre$ersed. This re$ersed flo0 pic:s up thesphere and carries it round the pro$er loop for the first pass. T0o sphere detectors aremounted in the pro$er loop, and the internalpipe $olume 6et0een these detectors isalready :no0n.

5s the sphere passes sp#ere detector B&B, asignal to the flo0 computer records theflo0meter reading at that point.

"hen the sphere passes sp#ere detector B7B,a ne0 flo0meter reading is recorded.

The difference 6et0een these t0o meter readings, representing the metered $olume of the pro$er loop, is no0 computed and stored.

The cali6ration sphere, at the end of the firstpass, is no0 held against the other 6uffer.

The flo0 computer no0 turns the 4=0aydi$erter $al$e through another 2- degrees tostart the second pass.

The second pass is no0 completed as a6o$e,6ut 0ith the oil f lo0 re$ersed.

The flo0 computer 0ill then a$erage the t0ometered $olumes from the first and secondpasses and compare this a$erage 0ith the:no0n $olume. 1f the $olume recorded 6y themeter under test is the same as the :no0n

$olume then the meter has 6een proed.

1f there is a discrepancy 6et0een the measured$olume and the :no0n $olume, the flo0computer 0ill calculate a correction factor andthen apply this to the meter under test. 5nother meter pro$ing run 0ill then ta:e place.

"hen the flo0meter reading (including anycorrection factor) falls 0ithin -.& of the :no0n$olume, 0ithout ad;ustment, for at least fi$econsecuti$e pro$ing runs, it is classed as 6eing

accurate.

Sampling Sstems

1t is not only important that the crude oil ismetered accurately. 1t is equally important togather information on the nature of the oil 6eingpumped. The chemical and physical nature of the oil may change 0ith time, as may the le$el

of contaminants, such as 0ater or solids, stillpresent after the separation process.

5 sampling sstem must therefore 6einstalled to determine the precise nature of theliquid 6eing pumped.

Sampling systems ha$e t0o main functions

sampling for metering sampling for analysis

Sampling for metering in$ol$es the use of anonline density measuring system. This system

continuously samples the fluid and passes thedensity results to the flo0 computer. Thecomputer then com6ines $alues for density,pipeline pressure and temperature to calculatethe mass flo9.

Sampling for analsis is carried out 6y asecond system. 5t regular inter$als, a pumpe8tracts a small amount of the fluid 6eingmetered, and these small samples are storedin a sample ;ar or similar $essel. Periodically,this com6ined fluid sample is ta:en a0ay to 6e

analysed in detail.

5n on=line ;asic sediment and 9ater 7S+/system is also installed on most oil handlingfacilities. The 3SU" analyDer ensures that the0ater and solids content of the crude does note8ceed pre=set limits (typically ?less than ?)0ithout a 0arning 6eing transmitted to theoperator.

The automatic sampling systems descri6eda6o$e are usually 6ac:ed up 6y samples ta:enmanually 6y the operator, as a chec: on theautomatic systems.

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Oil Pumping and MeteringSection ! – Pig "aunc#ing $acilities

1n pre$ious sections, 0e ha$e loo:ed at theequipment used to pump the oil. 1 ha$e descri6edtypical metering systems and ho0 0e pro$e thatthey are accurate. Sampling and analysis ofthe crude oil 0ere touched upon.

1n Figure 0e sa0 that the last stage in a crude oilproduction facility is normally the pig launc#er =the final item of equipment on the installation6efore the oil enters the main oil pipeline..The oil 0hich flo0s through the pipeline may ha$e

a small amount of residual 0ater in it. There may6e traces of sand, or 0a8 may 6e deposited fromthe oil as it cools do0n. 5ll of these materials maysettle out and affect the efficiency of the pipeline.

#e$ices called pigs may then 6e pumped throughthe pipeline, from the pig launc#er , to remo$e the0ater or sediments 0hich ha$e settled out from theoil.

Pig should from a reasona6ly tight fit inside thepipeline, in order that

• they perform their cleaning duties effecti$ely• they are efficiently transported through the

pipeline 6y the fluid flo0

3y the 0ay, there are t0o main e8planations gi$enfor the name Epig 6oth of 0hich are equallyunli:ely.

• the first is that the original pigs 0ere madefrom stuffed pigs:ins, send through 0aterpipelines to clear them out

• The second is that early pigs 0ere made of0ood, 0ith metal 6ands around them to help0ithstand constant ru66ing against the 0all ofthe pipeline. 5s they tra$elled along the

pipeline they ?squealed li:e pigs? as the metal6ands scraped along the pipe

1 0ill lea$e you to choose 0hich one you 6elie$e.

Tpes of PigPigs come in a $ariety of shapes and siDesdepending on the ser$ice 0hich they are intendedto perform.

Figure / on page 4 illustrates a fe0 of thedesigns a$aila6le. Their main uses are as follo0s9• the s(ueegee pig is often used for separating

different liquids or gases 0hen pipelines are6eing filled or emptied, or 0hen the samepipeline is 6eing used for different products. 1t

may also 6e used for light0eight cleaningduties and for de=0atering gas pipelines

• the ;rus# pig is used for cleaning and de=0a8ing pipelines. (Scrapers may also 6eincluded in the design). 3rush pigs in liquidser$ice often incorporate a series of pipes0hich pro$ide liquid channels through the pigcentre. Some of the liquid 6ehind the=pig 0illpass through the pipes and, 6ecause of theangle at 0hich these pipes are set, the pigrotates, thus impro$ing the 6rushing effect. 1n

addition, the ;etting action this causes ahead tothe pig stops a 6uild up of de6ris at that point.

• the sp#ere is used mainly to de=0ater gaspipelines 6ut it is occasionally used for $erylight cleaning 0or: on oil pipelines

• the foam pig is most often used for the initialde=0atering and cleaning of pipelines. 5ny0elding rods, or other sharp o6;ects 0hich mayha$e 6een left in the pipeline, em6ed

themsel$es into the foam as the pig passes 6y

• the foam ;rus# pig is used in light0eightcleaning ser$ice, usually on gas pipelines

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5 $ery specialised pig is sho0n in $igure 2!.Thisis the aliper pig or "inalog pig.

5s this type of pig tra$els along the pipeline,t0o 0heels, positioned near the centre of thepig, press against the 0alls of the pipe andrecord ho0 far the pig has tra$elled.

5t the same time a series of fingers, mountedat the 6ac: of the pig, slide along the 0alls ofthe pipe and measure its diameter.

The information thus collected is recorded ona chart 0hich is 6uilt into the pig. The chartcan 6e analysed on arri$al, to re$eal $ariations

in internal diameter (caused, perhaps, 6ydents or corrosion pitting) and precisely 0herethese $ariations occur.

Pigs are 6ecoming more sophisticated and,these days, are capa6le of measuring andrecording a 0ide range of data related to thecondition of the pipeline and contents.

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Pig "aunc#ers

"e 0ill no0 ta:e a loo: at Figure /&, 0hich sho0s the 6asic layout of apig launcher, and thin: a6out ho0 it operates



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nder normal conditions, the crude oil supply6y=passes the pig launcher and f lo0s throughale D directly into the pipeline.

To load a pig into the pig launcherC

• ale 7 and ale C should 6e closed

• the pig launcher must 6e de=pressurisedand drained of liquid

• 0hen these steps are completed, the piglauncher door = door & = is opened and thepig placed inside the launcher

• door & is then closed

• the pig launcher is refilled 0ith liquid andre=pressurised using the pressurisingale

• the pig launc#


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too short, and it may hang on a 6endallo0ing the flo0 to 6ypass it

al0ays ensure that the pig is properlypositioned in the launcher so that it 0ill

lea$e cleanly 0hen the flo0 is di$ertedal0ays remem6er to re=set the >piglaunched> de$ice 6efore you launch thepig, other0ise you cannot tell 0hether ithas entered the pipeline or not

5s 1 ha$e already emphasised, opening andclosing pig launchers is potentially dangerousand, 6ecause of this, most of the launchingfacilities are fitted 0ith safety systems. Thesepre$ent the operator from opening the 0rong$al$e or, 0orst of all, opening the launcher

door 0hilst the launcher is open to thepipeline.

Safet Sstems


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Summar of Section !

1n this section 0e ha$e loo:ed atC

• The reasons 0hy 0e need to pig a pipeline

• The different types of pig 0hich may 6e used

• 5 typical pig launcher and ho0 to launch a p ig

• 5nd, $ery 6rie fly, the need for safety systems

"e 0ill no0 loo: at a typical Oil Pumping and !etering

system and see ho0 it compares 0ith 0hat 0e ha$e learnedso far. 3efore that, ho0e$er, try the follo0ing Test


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Oil Pumping and MeteringSection %- & Tpical Oil Pumping and Metering Sstem

1n this section 0e 0ill ta:e a loo: at a tpicaloil pumping and metering sstem and seeho0 it relates to 0hat 0e ha$e co$eredpre$iously in this nit.


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Figure /7 C 5 Typical 3ooster Pump System

5fter a shutdo0n, PSLL creates a potentialpro6lem. 1f the pressure at that stage is6elo0 the setting of PSLL, the pump cannot6e re=started. 5 shutdo0n signal is still

6eing sent from the Pressure S0itch Lo0=Lo0. Something must 6e done to allo0 thepump to restart.

The pro6lem is o$ercome 6y, automatically,6ypassing PSLL for - seconds 0hen thepump is started. This allo0s sufficient timeto 6uild up enough pressure to re=set thes0itch. 1f the increasing pressure does notre=set PSLL 6efore the - seconds ha$eelapsed, then the pump 0ill shut do0nagain. This system is called a time-

pressure race, i.e., the pump is racingagainst time to generate sufficient pressureto re=set the s0itch.

The discharge of the pump is also fitted 0itha pressure s9itc# #ig# PS8/ and apressure s9itc# #ig#-#ig# PS88/. PS*0ill gi$e an alarm and PS** 0ill cause thepump to shut do0n in the e$ent of highpressures, perhaps 6ecause of pro6lemsdo0nstream.

The discharge of the 6ooster pump is fitted0ith a minimum flo9 non-return aleSF 1/) 0hich 0e ha$e already descri6ed inSection /, Page and Figure . Topre$ent the continuously re=cycled oil from6ecoming progressi$ely hotter, it is routedall the 0ay 6ac: to the /nd stage separator$ia 8F 2.

The discharge from pump 5 no0 passesthrough a hand=operated $al$e, 6efore

;oining the flo0 from the other pumps.

The com6ined flo0 then passes throughle$el control $al$e L%@ /. This $al$econtrols the oil le$el in the /nd stageseparator. The separator le$el controller 0ill open this $al$e if the le$el rises, andclose it if the le$el falls. "e can see that,in the e$ent of a failure of supply to the/nd stage separator, the $al$e 0ouldclose completely and the 6ooster pumps0ould go on to minimum flo0.

5fter passing across "CF 2 the oil flo0s tothe sampling and metering sstems.


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Sampling Sstem

$igure 2? sho0s the layout of a typical sampling system.

Figure / C 5 Typical Sampling 5rrangement

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Metering Sstem

1n the metering system sho0n in $igure 2')1 ha$e included ;ust one meter run and apro$er loop. The meter run, 0hich 0e coulddesignate run B&B) is from upstream of the

inlet 6loc: $al$e 8F 1/ to do0nstream ofthe outlet 6loc: $al$e (MOF 1). 1n acomplete system there 0ould 6e three ormore parallel runs. 1 ha$e indicated this inthe dra0ing as additional runs>3> and>%>.

5 single pro$er loop is used and thereare connections 6et0een each run andthe pro$er, ena6ling it to 6e placed inseries 0ith any of the meters.

Figure /+ C 5 Typical !etering System


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"hen meter run >&> is in ser$ice, the normalflo0 pattern 0ould 6e through

• the inlet ;loc ale 8F 1/• the filter $/• the flo9 straig#tening anes

• the tur;ine meter • the flo9 control ale $CF 1/• the outlet ;loc ale MOF 1/

and from there to the pipeline oil pumps.

"hen the meter in run >5> is 6eing pro$ed,the flo0 0ould 6e through

• the inlet 6loc: $al$e (*@ )

• the filter (F)• the flo0 straightening $anes• the tur6ine meter • the pro$er loop 6loc: $al$e (!O@ /)• the 4=0ay pro$er loop di$erter $al$e

(!O@ ) the pro$er loop• the 4=0ay pro$er loop di$erter $al$e

(!O@ )• the pro$er loop flo0 control $al$e (F%@

/)

and from there to the pipeline oil pumps.

ote the flo0 computer in the dra0ing. 5> 0ere innormal ser$ice this 0ould 6e F%@ . 1fmeter>5> is 6eing pro$ed ho0e$er, the flo00ould 6e controlled $ia F%@ /. The flo0reading from each meter is fed to thecomputer $ia a flo0 transmitter (FT).

So, 0hen the meter in run >5> is 6eingpro$ed, the flo0 computer

• closes !O@ • opens !O@ /• transfers control of flo0 from F%@ to

F%@ /• allo0s flo0 to sta6ilise• operates !O@ to start first pro$ing run• operates !O@ again, to re$erse flo0

through pro$er and start second (andany further) pro$ing runs

• performs necessary calculations too6tain meter factor

5 fe0 other points to note are

) interloc:s are fitted to !O@ and !O@/ to ensure that these $al$es are at the

right setting (open or closed) 6efore themeter pro$ing starts

/) pressure relief $al$e PS@ is locateddo0nstream of the filter and upstream of the flo0 straightening $anes. 1f *@ ,!O@ and !O@ / are all closed for anyreason, the pressure inside the meterrun may rise due to any temperatureincrease. PS@ is fitted to relie$e thispressure

) to ensure the accuracy of the pro$erloop, the sphere is al0ays o$ersiDed 6y=/. This ensures a tight fit 6et0eenthe surface of the sphere and the 0allsof the pro$er loop. The sphere isreplaced on a regular 6asis, and it isnormally the first item to 6e changed ifthe accuracy of the pro$er loop issuspect

4) 5n independent contract company isoften used to pro$e the pro$er loop, say,on an annual 6asis


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Oil Pipeline Pumps

1f you loo: at $igure 2=, you can pro6a6ly see ho0 the oil pipeline pumping system 0or:s.

Figure /2 C 5 Typical Pipeline Pumping System


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1t is rather similar to the 6ooster pump layout,so 0e 0ill concentrate only on the importantdifferences• "hen the minimum flo0 system is

operating, crude oil is re=cycled from thedischarge to the suction of the pump and

is not routed 6ac: to a separator, as 0asthe case in the 6ooster pump layout. (Theseparators are upstream of the meters.Therefore, if the oil 0as re=cycled to theseparators, it 0ould pass through themeters t0ice, 0hich, of course, 0ouldintroduce errors into the flo0measurements)

• *o0e$er, 6ecause the pipeline pumps aretransferring a large amount of energy tothe oil, this direct re=cycling 0ould result ina rapid and su6stantial temperature rise.

To pre$ent this from occurring, a re=cyclecooler is fitted to cool the crude 6efore it isreturned to the suction of the pipelinepumps. Offshore, the re=cycle cooler0ould often use sea0ater as a coolingmedium (as sho0n in Figure /2) 6ecauseit is cheap and plentiful

$luid CouplingPipeline pumps ha$e a $aria6le speed dri$e.The speed at 0hich they operate is

determined 6y the pipeline pressure controller (0hich 0e 0ill loo: at later). li theline pressure is too lo0, then the controllerincreases the pump speed9 if it is too high, thepump speed is decreased.This speed $ariation may 6e achie$ed 6y afluid coupling 6et0een an 5% electric motorand the pump.Fluid couplings are also :no0nas #draulic couplings.

Figure -C 5 Fluid %oupling

Figure - is a three dimensional cut=a0aydra0ing of the coupling assem6ly.


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• an inlet shaft, connected to the dri$emotor

• an outlet shaft, connected to the mainpump

The inlet shaft dri$es an oil circulating pump.

The oil path is from the reser$oir, $ia a coolerand small holding tan:, into the circulatingpump suction. From the pump discharge, theoil flo0s to the scoop c#am;er.


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Figure a, 6 and c C Speed %ontrol sing a Fluid %oupling


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The position of the scoop tu6e 0illdetermine ho0 much po0er is transmittedacross the coupling.

• 1n Figure a the scoop tu6e is at

ma8imum e8tension, at a radius slightlygreater than the outer 6oundary of thecirculating oil. Therefore, all oil enteringthe scoop cham6er is >scooped> a0ay 6ythe open tip of the scoop tu6e andreturned to the reser$oir. The scoopcham6er is $irtually empty, and no oilremains for the runner to thro0 at theimpeller. Po0er transmission is thereforenil, and the main pipeline pump isstationary.

• 5t an intermediate e8tension of thescoop tu6e, (Figure 6), a ring of oilcan accumulate in the scoop cham6er6et0een the tip of the scoop tu6e andthe outer 6oundary. This limited $olumeof oil is no0 a$aila6le for the runner tothro0 at the impeller. 5n intermediatele$el of po0er can no0 6e transferredacross the coupling to dri$e the mainpump.

• 1n Figure c, the scoop tu6e is atminimum radius, the oil retained 0ithinthe scoop cham6er is at a ma8imum,and full po0er transfer is ta:ing place.

Pipeline Pumping Pressure

Ieturning to Figure /2 again, the oil pipeline

pump speed is controlled 6y the speedcontroller (S%) 0hich ta:es its signal fromthe pipeline pressure controller.

1f the pipeline pressure is toe lo0. thesecontrollers 0ill speed up the oil pipelinepump 6y shortening the e8tension of thescoop tu6e.

1f the pressure is too high, thecontrollers 0ill slo0 do0n the mainpump 6y increasing the radius of the

scoop tu6e.

Pressure Transmitter

Finally, ;ust upstream of the main outlet$al$e S#@ / is a pressure transmitter (PT)0hich sends a telemetry signal to the localcontrol room, to the share (in offshorelocations), and to other oilfields sharing thesame pipeline facility.

This safety feature is required to pre$ento$er=pressuring the pipeline.


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Pig "aunc#ing

The pig launc#ing facilit is illustrated inFigure /. 1t is similar to the=one 1 ha$edescri6ed pre$iously,

ormal flo0 through the system 0ould 6eC

• through S#@ /

• through !O@

• through S#@ , and then

• to the pipeline

4S,F 2 and 4S,F 3 are t0o emergencyshutdo0n $al$es 0hich are interloc:ed 0iththe S# system to ensure that the pipeline

pumps cannot 6e operated 0hen these$al$es are closed.

On an offshore installation, S#@ m ay6e situated on the sea 6ed. 1t is designedto ensure that no oil can f lo0 6ac: to theinstallation in the e$ent of platformmalfunction. 1t is only operated in e8tremeemergencies such as a fire or largo oil lea:.


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Figure /C 5 Typical Pig Launching System


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o0, 0ith reference to Figure / again, 0ecan list the steps in$ol$ed in launching a pig

1. chec: that the pig is undamaged, thecorrect siDe, and that the shape is

undistorted. Spherical pigs may 6epassed through a siDing ring to ma:esure that they are the right siDe.

2. ensure that the pig signalling de$ice(SV) has 6een re=set, ready to tell us0hen the pig has 6een launched

3. chec: that !O@ /, !O@ and *@ areclosed so that 0e may de=pressurise thepig launcher

!. 6egin the de-pressurisation process6y opening *@ , allo0ing pressure inthe pig launcher to 6lo0 the oil itcontains to the drain system

%. as the pressure falls, the high pressures0itch (PS*) 0ill sho0 that the pressureis not high. Then the lo0 pressures0itch (PSL) 0ill sho0 that the pressureis lo0

6. 0hen this situation is reached, 0e can

open *@ / to the $ent system and allo0the pig launcher and $ent systempressures to equalise. 5s this occurs,the remainder of the oil 0ill drain to thedrain system through *@

?. confirm that pressure is off the piglauncher 6y chec:ing a pressure gauge(PG). Then close *@.

'. Open *@4 to allo0 nitrogen (/) to flo0through the pig launcher to remo$ehydrocar6on gases. %lose *@ 4 and*@/

=. Open the pig launc#er door

1>. "oad the pig) ensuring that it is past theinlet from MOF 2

11.close the pig launcher door andpurge air from the launcher (0ith

nitrogen) 6efore re=pressurising. Thereason for purging is to pre$ent ane8plosion 0hen 0e 6ring thepressure up to normal operating le$el(in our e8ample, the purgingoperation is carried out 6y re=opening *@ / and then *@ 4. Thisallo0s a small amount of nitrogen todisplace air to the $ent system $ia*@ /)

12. 0hen all air has 6een displaced, close*@ 4 and *@ / and allo0 pressure to6uild up to the pipeline operatingpressure 6y opening *@ . 5s this

occurs, PSL 0ill tell us that the pressureis not lo0 and PS* 0ill finally tell us thatthe pressure is high. "hen these t0os0itches ha$e gi$en their indications, 0e0ill close *@

13. open MOF 3 and then MOF 2. "e open!O@ first 6ecause 0e do not 0ant asudden flo0 of oil through the piglauncher to try to force the pig through!O@ as it is opening

1!. 0hen !O@ / is fully open, close !O@ to di$ert the flo0 through the piglauncher. "e :eep closing !O@ untilthe flo0 launches the pig. "hen the pigenters the pipeline, it 0ill hit the pig

enters the pipeline, it 0ill hit the pigsignalling de$ice (SV). This 0ill then tellus that the pig has passed this point.

1%. Ie=open !O@ , close !O@ / and !O@, to return the system to normal.


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o0, finally, try this Test ourself , 0hich co$ers some of the topics 0e ha$ediscussed in Section &.Summar of Section %

1n this section 0e ha$eC

• Loo:ed at the main design features of a typical oilhandling and metering system

• 8amined the laylout of a ;ooster pump unit and, inparticular, ho0 it may 6e controlled

• #iscussed the :ey elements of a sampling sstem andnoted that densit and 7S+ are measuredautomatically

• "or:ed through the operation of a metering sstemand, in particular, a meter pro$ing loop

• Loo:ed at a typical arrangement of the main pipelinepumps) and compared this arrangement 0ith that for6ooster pumps

• #iscussed the main design features of a fluid driesstem) and ho0 it may 6e used to control pumping rate

• #escri6e the procedure for launc#ing a pig to thepipeline

Test ourself 2. "hat do you understand 6y a time-pressure raceB

/. 1n pig launching operations, 0hat does the flag doB

. "hat do 0e mean 6y the meter factor B

4. 1n the case of the 6ooster pumps, 0hy does the minimum flo0system re=cycle oil 6ac: to the second stage separator, and not

directly to the 6ooster pump inletB

&. The minimum flo0 system for the main pipeline pumps re=cyclesoil directly to the pump suction. "hy does this arrangement differfrom that for the 6ooster pumpsB

7. "hat types of analysis does out sampling system performcontinuously on the oil flo0B


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@nit Summar

1n the course of this nit on Oil Pumping and Metering, 0e ha$eC

• loo:ed at some of the theories 6ehind the operation of centrifugal pumps) including the 6eha$iour of fluids, centrifugalforce and energy.

• #etailed the component parts of a centrifugal pump) and the role each, plays in its operation

• 8amined the main design features of a metering and sampling sstem) and ho0 it is controlled and operated

• Familiarised oursel$es 0ith the layout and operations of a pig launc#ing facilit

• #iscussed the main design and operational aspects of a tpical oil pumping and metering sstem

o0 go 6ac: to the Training Targets on Page 4 of this unit and satisfy yourself that you are a6le to meet those targets.


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C#ec ourself 1

Specific gra$ity of gasoline

mass of one gallon of gasoline

mass of one gallon of 0ater (reference)

+.& l6s

-.+&- l6s

Specific gra$ity of 6rine

mass of one gallon of 6rine

mass of one gallon of 0ater (reference)

l6s

.- l6s

C#ec ourself 2

@elocity of the car C

+- :ph &- metresA sec

'inetic energy of the carC J 8 ---'g 8 (&-mA sec 8 &-mAsec) /&---- ;oules

@elocity of the truc:C- :ph +. metresAsec

'inetic energy of the truc:C J 8 /---'g 8 (+.mA sec 8 +.mAsec) 7++2-- ;oules

Therefore, the car rigs >he greater ineticenerg

C#ec ourself 3

- feet head of 0ater e8erts a pressure of4. pounds per square inch,

S.G. of gasoline -.+&

*ead Pressure of - feet of gasoline 4. 8 -.+& .7+ pounds per squareinch.

7 feet head of 0ater e8erts a pressure of7.2 pounds per square inch,

S.G. of 6rine .

*ead Pressure of 7 feet of 6rine 7.2 8 . .7/ pounds per square inch


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C#ec ourself !

6. the static suction line pressurec. the PS*a. the pressure at 0hich gas or $apour is

released

The P * represents the minimum designpressure to preent gas or $apour release andshould therefore 6e a6o$e this gas A $apourrelease pressure 6y a safe margin

The static suction head pressure 0ould normally6e maintained at a6out - a6o$e the PS*.

C#ec ourself %

- differential pressure +. flo0 4.2 galsA min

4- differential pressure 7./ flo0 .7 galsA min

Therefore the flo0 rate 0ould fall 6y4.2. W .7 -. galsA min

C#ec ourself 6

"hen pumping /- cu6ic metres per hourthis pump 0illC

• require a minimum of .4 metres head of liquid PS*

• de$elop & metres total head of liquid

• consume + :ilo0atts of po0er

• operate at / efficiency

appro8imately

C#ec ourself ?

"hen pumping 4- cu6ic metres per flour thispuma 0ill 9

• require a minimum of .2 metres head ofliquid PS*

• de$elop 4 metres total head of liquid

• consume . :ilo0atts of po0er

• operate at +& efficiency

appro8imately

C#ec ourself '


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C#ec ourself =

.- of 7-,--- 66lA day 7-- 66lA day 7-- 8 7& 66lA year /2,--- 66lA year (assuming, of course, that the installation produces at that rate 0ithout interruption).

5t Z/& per 6arrel, this error is $alued at a6out Z&.& million per year.

This e8ample emphasises $ery effecti$ely the importance of accuracy in the metering process.


76/77

C#ec ourself 1>

. densitometer 5n instrument, installed 6et0een

6ooster pumps and metering system,to measure the density of the pipelinefluid.

. 3ooster pumps Located upstream of the metering and

sampling system (to discourage gasA $apour6rea:out).

/. Flo0 straightening$anes

1nstalled upstream of a flo0 meter tosmooth out flo0 and pre$ent s0irling.

+. Pic:=up coil Part of a tur6ine meter, used to sense andtransmit speed of rotation.

. 4=0ay di$erter $al$e Part of a meter pro$ing loop, allo0ingflo0 to 6e re$ersed for a second passof the sphere

2. Orif ice plate 5n essential part of the most common typeof differential pressure meter

4. $ena contracta This is cheating a l ittle 6it W the $enacontracta is the point in the flo0 rate ishighest and pressure lo0est.

-. Sphere detector Part of a meter pro$er loop, and signals the6eginning and end of a pro$er run, allo0ingthe meter reading to 6e recorded at thosepoints.

&. Pro$er loop 5 pipe loop of :no0n $olume in themeter pro$ing system, 0hich allo0saccurate cali6ration of the meter.

. Tur6ine meter The most common type of oil flo0 meter,located do0nstream of 6ooster pumps, filterand flo0 straightening $anes

7. 3SU" analyser 5n instrument, installed 6et0een6ooster pumps and metering system,to measure 6asic sediment and 0ater

(3SU") in the pipeline fluid.

/. 3loc: and 6leed$al$es

Located at $arious places in a metering run,allo0ing the run to 6e positi$ely isolatedfrom the rest of the process. The E6leed

facility allo0s the space 6et0een the t0o$al$e seals to 6e depressurised.


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C#ec ourself 11

. They are the only par[ of the pipelineSystem 0hich is regularly opened to theatmosphere.

/. The pig launcher must 6e =.

a) isolated 6orn the pipeline6) drained of liquidsc) depressurised

C#ec ourself 12

) "hen restarting the 6ooster pumps after a shutdo0n due to lo0 pressure, it 0ill6e necessary to 6y=pass the pressure s0itch lo0=lo0 (PSLL = see Figure /7) fora short 0hile. This gi$es the pump sufficient time to 6uild up enough pressure tore=set PSLL.

/) The flag is part of the pig launch indicator mechanism, and signals that the pighas passed that particular point in the system.

) The meter factor is a correction factor 0hich allo0s us to con$ert o6ser$ed flo0readings to true $alues.

1t is calculated during the meter pro$ing procedure, 6y comparing the true $alue ofliquid passing through the meter in a gi$en t ime, 0ith the $olume registered 6y themeter in the same timeC

meter factor true $olume of liquid passing through meter in a gi$en time

$olume registered 6y meter in the same time

4) Ie=cycling directly 6ac: to the pump suction 0ould cause the oil to 6ecomeprogressi$ely hotter. Ie=cycling to the separator 0ill gi$e the oil an opportunityto cool do0n.

&) The separators are upstream of the flo0 meters. 1f 0e re=cycled oil to theseparators, it 0ould pass through the meters t0ice and gi$e us a false flo0reading.

7) (i) density or specific gra$ity(ii) 6asic sediment and 0ater (3SU")

l l t : f d t il d l 6 t l i

oil pumping and metering part of the petroleum proce

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