pressure testing code requirements.pdf

7/28/2019 PRESSURE TESTING CODE REQUIREMENTS.pdf

http://slidepdf.com/reader/full/pressure-testing-code-requirementspdf 1/26N. Al-Khirdaji, AZTech Sr. Consultant

3.7 Pressure Testing – Code

Requirements and Best Practices• Hydrostatic testing

• Pneumatic testing

Pressure Testing• Pressure testing is used to determine the integrity of

pressure equipment and piping systems. It is based ondeterminin the abilit of a i in s stem to withstand ahydrostatic pressure that equals or exceeds the design pressure (test pressure depends on the type of test).

• The tests criteria are pressure history and leak detection.

• A test is conducted by isolating and pressurizing thevessel/piping, and then measuring the change in pressureover a specified time. At the same time, visual inspection

or ea s s con uc e .• The test pressure shall, unless otherwise specified, be in

accordance with applicable code (e.g., ASME BPVC,ASME B31.3, ASME B31.4, API 1110, etc.).



Some Pressure Testing Requirements

• Accurate and precise temperature data are

essential to mathematicall reconcile tem erature

and pressure changes observed during testing of

buried pipelines and to certify absence of leakage.

• The API recommended practice applied by the

project specifications explicitly requires

temperature measurements to be made in

increments of 0.1°F (0.05°C) and that a

continuous-recording temperature measurementdevice be employed to provide a permanent record

of pipeline temperature versus time.

Some Pressure Testing Requirements

• During a typical pipeline hydrostatic test, pressuremeasurements are taken and recorded at 15 or 30-minute intervals using a dead weight test gaugecapable of precision of ± 0.5 psi, or better.

• Each set of measurements is reconciled and thecalculated net test volume is plotted on a timescale for each interval.

• Trends on the volume-time plot can indicate small

leaks after a short monitoring period.• After the elapse of the required test holding time,

typically specified as 8 to 24 hours, the presenceor absence of leaks is indicated with a high degreeof certainty.



Pressure Testing of Buried Pipe

• Economic and construction considerations for pipeline projects typically require installation of pipe and back filling of the pipe trench before pressure testing.

• Since visual leak inspection of the buried pipe isnot possible during testing, it is necessary toreconcile observed changes in test pressure withchanges in temperature to verify the absence of

.

• A mathematical calculation is necessary to make

the reconciliation, and the temperature of the pipeand its contents are the most critical of severalelements to be considered.

Pressure Testing of Buried Pipe

• - -, , , pipeline 15,000 feet long, tested with water starting at 50°F, will lose about 9 pounds per square inch (psi) of pressure due to a 1°F cooling.

• The same pipeline tested at a starting temperatureof 70°F will lose about 23 psi for each 1°F of

.• Even more dramatically, this same pipeline, if leak

tested with diesel fuel or jet fuel, would lose about80 psi for each 1°F of cooling during a typical test



Pressure Test Planning - 1

• To achieve an accurate and representative test,adequate planning is required.

• Some necessary information needs to be gathered prior to the test. The following information should be gathered days or weeks before the actual test: – presence of pressure relief devices,

– test medium information,

– delineation of individual pipeline test segments, and

– requ re es ns rumen accuracy.

• Just prior to test start-up, pre-test calculations

should be performed to detect the presence of entrained air.


• The presence of pressure relief devices must

e e erm ne pr or o e es .

• Usually these devices have a set pressure at or

5 – 10 % above the maximum allowable

operating pressure.

• prior to conducting the test.




• The presence of a significant amount of

trappe a r w n e es e p pe ne can e

problematic to test accuracy.

• When testing a pipeline with water, trapped air

can be eliminated by filling the tested line at a

ra id enou h rate thereb creatin a

completely turbulent interface between the

incoming water and the displaced fluid.

Pressure Test Preparation

• Pressure, temperature and time recorders should be

.

recorders used to indicate and record test pressure

shall be dead weight tested for accuracy according to

a procedure, dependent of type of equipment.

• All piping should be adequately supported before the

.

should be blocked to prevent movement.




• If there is a deviation of more than 2% between gauge,

the equipment recalibrated.

• Piping joints and welds shall not be insulated or physically covered until satisfactory completion of testing in accordance with this specification, exceptfor painting of prefabricated welds.

• A p p ng s a e a equate y supporte e ore t e pressure test. Spring or other variable type supportsshall be blocked to prevent movement.


• ,through body tested. First block valve for pressureinstruments shall be included in the test.

• Piping containing check valves shall have thesource of test pressure on the upstream side. If thisis not possible, the check valve disc shall be

.• Where the test pressure > the maximum allowable

test pressure for valves, the valves shall be blindedoff on the side to be tested, or removed andreplaced by dummy spools




• Turbines, pumps, compressors and vessels.

• A list shall be prepared for sensitive equipmentthat shall be removed, blocked off or isolatedduring testing, such as relief valves, inlineinstruments, turbines, pumps, compressors and

.

This list shall be a part of the test procedure


• Piping joints and welds should not be insulated or

testing in accordance with this specification, exceptfor painting of prefabricated welds.

• Minimum of one gauge shall be positioned at thehighest point and one recorder to be positioned at thelowest point.

• ccuracy o pressure gauge s a e at east - atfull scale and 1-2% for the recorder. The test pressureshall be within 60% of the gauge range.



Test Media

• For hydrostatic testing the test medium shall in,

suitable liquid may be used if:

– The piping or inline equipment would be adverselyaffected by water.

– If the liquid is flammable, its flash point shall be atleast 49°C and consideration shall be iven to the environment.

– The liquid is approved by the Owner

Test Media

• The chloride ion content of the water used for

100 ppm and the line shall be properly drained soonafter testing. The pH of the water shall be between6.5 and 7.5.

• For pneumatic testing, the test media shall be oil free,dry air or any inert gas. The extent of pneumatic

.and requirements generally apply.



Duration of Test Pressure

•sufficient length of time to permit visualexamination to be made of all surfaces, welds andconnections, but not less than thirty minutes.

• A one hour test duration shall apply for pipingsystems with pressure rating class 600# and above.

• are s a e ta en to ensure t at over-pressur ngdue to static head does not take place.

• The piping systems shall not show any sign of plastic deformation or leakage.

After Completion of Test

• The tested systems shall be depressurized by opening

.

• After depressurization, all vents and low point drain

valves shall be opened and the system shall be

thoroughly drained where the test medium is water.

• Where required, blowing by dry air or Pressurized

be performed.



Pneumatic Testing

• Pneumatic testing is normally used in cases where

tolerated or when water of suitable quality is notavailable.

• Typically, Owner approval is required before pneumatic testing is to be performed. Additionally, because of the potential energy of the compressed air

,safety precautions and procedures have to be

implemented.

Stored EnergyIn Pressurized Gas Vessel or Piping

• When a gas is compressed, energy is stored in it. If the

energy s re ease n an un avora e way, w cause

damage.

• Stored energies in excess of 100 kJ are considered

high hazard.

• Sometimes it is helpful to think of stored energy in

terms o grams o tr n troto uene .One gram of TNT contains 4.62 kJ of energy

0.01 lb TNT = 14,240 ft-lb of stored energy



Stored Energy

In Pressurized Gas Vessel or Piping

-1

Vh = The volume of the vessel.

Ph = The absolute pressure of the vessel.

U =h h

γ - 1{ 1 – (P1/Ph)

γ }

Pl = The absolute pressure to which the vessel would drop if it burst,

generally one atmosphere (14.696 psi or 101,300 Pascal). A Pascal

is a Newton per square meter.

γ = The adiabatic exponent or ratio of specific heats, Cp/Cv. (= 1.67

for monatomic gases; 1.4 for diatomic gases; 1.3 polyatomic gases)

Example: Consequences of Leakage or Rupture of Pressure Vessel and Piping

= .

Vh = 1.0 m3 (35.3 ft3)

Ph = 10 atm (150 psi) gage or 11 atm absolute or 1.1 MPa

Pl = 1 atmosphere or 100 kPa or 14.7 psi

U ={(1*105 N/m2)(1.0 m3)/(1.4-1)}{1-[1*105 N/m2/ (1*105 N/m2)]1.4 -11.4 }

The stored energy is 1.4 MJ (N-m is a joule), which is equivalent

to 0.3 kg of TNT (1 kg TNT = 4.62 MJ)

U = 1.4* 106 N-m



Potential EnergyStored Volumes of Ideal Gas at 20° C

PRESSURE, psig TNT EQUIV., lbs. per ft3

10 0.001

100 0.02

1000 1.42

10000 6.53

TNT equiv. = 5 x 105 Calories/lb

Preparation for Pneumatic Testing

. ,w/mechanical seals, heat exchangers, etc. thatare incapable of withstanding the test pressureshall be blanked off before pressure testing. In-line components such as filters and strainers mayremain.

. the Test Pressure, or that are otherwisesusceptible to damage, shall be removed or

blanked from the Pipeline being tested, or shall be replaced with a pipeline spool.



Preparation for Pneumatic Testing3. Suitable warning signs, barricades or other safety

during testing in the event of sudden release of pressure. Pneumatic pressure testing should be performed during off-shift hours, where possible, toreduce the potential for personnel injury.

4. Visual Examination of the piping systems shall be

pressure tests.

Preparation for Pneumatic Testing5. All joints and welds must be uninsulated, before

.

6. If the air supply used is moist, no testing will be

permitted unless ambient temperatures are expected

to be above 32 F during the full duration of the test.

7. This pressure test method is restricted to 12" NPS

, by the owner.



Preparation for Pneumatic Testing• , ,

provided by a compressor, which is free from dirt,oil, weld slag, construction debris, and other foreignmatter, shall be used for the pneumatic test.

• Test Apparatus: All gauges used for field testingshall have a suitable range and a dial scale not less

" .so that the test pressure of the system falls between

40% and 80% of the gauge scale range. Gauges shall be out of "new" quality and in first class workingcondition.

Preparation for Pneumatic Testing

• A pressure relief device shall be installed in

e es oop an s a e se o re eve a e

greater of 25 psig or 10% above the defined

Test Pressure

• Test Pressure: The Test Pressure shall be

e ual to 110% of either the desi n ressure of

the piping system, or its weakest component.



Test Procedure

• Test Procedure: The pressure source shall be.

necessary for the operator to leave the pressuresource, he should first relieve the pressure in the testloop.

• A preliminary check shall be made by pressurizingthe test loop to not more than 25 psig. At each

,for one minute before processing to a higher pressure

Test Procedure

The following typical procedure shall be used:

. ose a va ves n e ne an or an o a anges.

2. Open the valve supplying the test fluid to the pipe system

slowly until the pressure gauge indicates 25 psig.

3. Close the valve supplying pressure.

4. Observe the pressure gauge. If the pressure holds steady

for one minute, proceed to Step 5.

5. Open the valve supplying pressure.



Test Procedure

6. Increase the test pressure in the line by 25 psi.

7. Close the valve su l in ressure.

8. Repeat Steps 4, 5, 6 and 7 until the Test Pressure isachieved.

9. Hold the Test Pressure for a period of time sufficient to permit a thorough inspection of all joints for leakage, butnot less than 10 minutes. The pneumatic pressure testresults are acceptable when there is no evidence of ea age or seepage an no ecrease n pressure s own on

the test gauge during the test.

10. Relieve the pressure in the test loop.

Test Procedure

• Repair any leaks found in the test loop. After

repa rs, re es e es oop per eps ru

above at the Test Pressure.

• Retesting also requires a stepwise pressure

increased in 25 psig increments.



Test Record

• Test Record: The test shall be witnessed by the

required by regulations).

• Records of the pressure test shall be maintained bythe per company policies as identified on the PressureTest Record Form.

• Records should include the test date, identification of t e p pe ne teste an t e type o pressure test usewith reference to the appropriate project andmaintenance files.

Pressure Tests – Pressure Vessels130 Hydrostatic test pressure for pressure vessels

110

100

Pneumatic test pressure for pressure vessels

Maximum Allowable working Pressure, MAWPMaximum relief device settingRetest pressure for all vessels and systems

e n t o f M A W P

80

Maximum operating pressure, MOP*

* Recommended range is 10 to 20% below the MAWP

P e r

≈



Pressure Testing of Liquid

Petroleum Pipelines• A pressure test is performed to test for pipeline

s reng an ea age, an o sa s y s a u ory

regulations.

• A pressure test includes: site preparation,

temperature measurement and monitoring,

time of events i eline ackin and

pressurization, strength testing, leak testing,

and pipeline test documentation.

Hydrostatic Testing of InternalPressure Piping (ASME B31.4)

•existing liquid petroleum pipelines.

• It recommends minimum procedures to befollowed, suggest equipment to be used, and

points out factors to be considered duringhydrostatic testing of liquid petroleum pipelines.

• s suggests proce ures t at are ase onsound engineering judgments, but certaingovernmental requirements may differ from this

procedure set forth in this RP. Such requirementssupersede the RP.



Hydrostatic Testing of Internal

Pressure Piping (ASME B31.4)• Portions of i in s stems to be o erated at a hoo

stress of more than 20% of the specified minimumyield strength of the pipe shall be subjected at any

point to a hydrostatic proof test equivalent to not lessthan 1.25 times the internal design pressure at that

point (see para. 401.2.2) for not less than 4 hours.

•hoop stress, based on nominal wall thickness, in

excess of 90% of the specified minimum yieldstrength of the pipe, special care shall be used to

prevent overstrain of the pipe:


Pressure Piping (ASME B31.4)

–

pressured components are visually inspected during

the proof test to determine that there is no leakage

require no further test. This can include lengths of

pipe which are pre-tested for use as replacement

sections.

– On those portions of piping systems not visuallyinspected while under test, the proof test shall be

followed by a reduced pressure leak test equivalent

to not less than 1.1 times the internal design

pressure for not less than 4 hours.




Pressure Piping (ASME B31.4)• ,

except liquid petroleum that does not vaporizerapidly may be used provided :

– The pipeline section under test is not offshore and isoutside of cities and other populated areas, and each building within 300 feet of the test section isunoccupied while the test pressure is equal to or greater than a pressure which produced a hoop stress of 50% of the specific minimum yield strength of the pipe.

– The test section is kept under surveillance by regular patrols during test; and

– Communication is maintained along the test section.


Pressure Piping (ASME B31.4)• If the testing medium in the system will be subject to

,made for relief of excess pressure. Effects of temperature change shall be taken into account wheninterpretations are made of recorded test pressures.

• After completion of the hydrostatic test, it isimportant in cold weather that the lines, valves, and

damage due to freezing.



Hydrostatic Testing - 1

• Hydrostatic testing is used to conduct strength tests on:

– new pipes while in the manufacturing process, as well as

– at the completion of pipeline installation in the field prior to being placed in service.

• Hydrostatic testing is also used, at times, for integrityassurance after a pipeline is in operation.

•assessment method when the pipeline is not capable of

being internally inspected or if defects are suspectedthat may not be detectable by internal inspection smart

pigs.


•capacity of a pipeline and may identify defects thatcould affect integrity during operation.

• Testing is done to a pressure that is greater than thenormal operating pressure of the pipeline. This

provides a margin of safety.

• e test stresses t e p pe ne to a pre eterm ne percentage of its specified minimum yield strength(SMYS). Typically pressures range from 93% to100% of SMYS, and the test is generally held for eight hours.




• If stress corrosion cracking (SCC) is suspected, the

SMYS or higher for 30 minutes to an hour.

• Axial flaws such as stress corrosion cracking,

longitudinal seam cracking, selective seam corrosion,

long narrow axial (channel) corrosion and axial

Leakage (MFL) pigs and are better detected with a

hydrostatic test.


•large quantities of test water, which in some areasmay be difficult.

• Once used, the test water may contain trace quantitiesof petroleum products, which may require treatmentof the water prior to discharging or disposal.

• y rostat c test ng requ res t e p pe ne to e out oservice for a period of time thus potentially curtailingthe availability of gasoline, jet fuel, diesel fuel, crudeoil, and/or home heating oil at the delivery point.



Leak Testing

• Leak testing may be used to find leaks in a newly

,

established system where an apparent loss of integrity

has been experienced.

• If they exist, leaks typically occur at joints (or from

through wall defects).

,

operating pressure.

Leak Testing

• Leak testing does not verify pressure rating or - .

and the pressure ratings of the installed componentsare the sole determinants of system pressure ratingand long-term performance.

• Safety is of paramount importance. Leak tests canapply high stress to untried joints and parts in the

.catastrophic rupture. In some cases, leakage mayimmediately precede catastrophic rupture.



Some US Regulations

• § 192.507 Test requirements for pipelines tooperate at a hoop stress less than 30 percent of SMYS and at or above 100 psi. (689 kPa).

• Except for service lines and plastic pipelines, eachsegment of a pipeline that is to be operated at ahoop stress less than 30 percent of SMYS and ator above 100 si 689 kPa must be tested inaccordance with the following:

(a) The pipeline operator must use a test procedurethat will ensure discovery of all potentiallyhazardous leaks in the segment being tested

Some US Regulations

, ,

20 % or more of SMYS and natural gas, inert gas, or

air is the test medium:

(1) A leak test must be made at a pressure between 100 psi.

(689 kPa) gage and the pressure required to produce a

hoop stress of 20 % of SMYS; or

(2) The line must be walked to check for leaks while thehoop stress is held at approximately 20 % of SMYS.

(c) The pressure must be maintained at or above the

test pressure for at least 1 hour.




• Each test loop should be provided with a low pointi in connection for h drotest water su l .

High point vents shall be provided to permit theventing of air from the test loop--to ensure that the

pipeline is completely filled with water.

• Test Pressure: The Test Pressure shall be equal to

– 150% of either the design pressure of the piping, .

– 130% of either the design pressure of the pressure

vessel, or its weakest component.(adjusted to new and cold conditions)

Service Tests

• Service tests are usually applied to non-critical

-

hazardous services. Illustrative examples:

(1) Non-flammable and non-toxic fluids

(2) Design pressures less than 150 psig

(3) Operating temperatures range: -20 to 366o F.

• The criteria for application of service tests should beclearly established in the owner specifications.


http://slidepdf.com/reader/full/pressure-testing-code-requirementspdf 26/26

Pneumatic Tests

• Pneumatic testing is normally used in cases where

tolerated or when water of suitable quality is notavailable.

• Typically, Owner approval is required before pneumatic testing is to be performed.

• Additionally, because of the potential energy of t e compresse a r gas) n t e system un er

pneumatic testing, special safety precautions and procedures have to be implemented.

• Test pressure for pressure vessels = 110% X DP

Leak Detection

• Technology is available to detect leaks from gas.

• One approach involves the use of sensitive sensors on board low- flying surveillance airplanes that fly alonghe pipe route.

• Another approach entails the use of methods basedon analysis of time series of pressure and/or flow

m a ance ecause t ese present some we nownreaction to leaks. A software-based system istypically used for such application.

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