air and hydraulic tests

8/10/2019 Air and Hydraulic Tests

1/34

AIR AND HYDRAULIC TESTS

PERFORMED ON PROCESSEQUIPMENTS, ITS

IMPORTANCE ANDLIMITATIONS


2/34

Why Pressure testing is required?

It is the last physical quality test in thefabrication process.

Performed prior to placing the system to

service. Done in a controlled environment.

Preferred mainly due to safety considerations.


3/34

Types of Pressure tests

Pressurized Fluid : leaks are detected byspecialized fluid pressure gauges or electronicsensors.

Pressurized Air/ Gas: leaks are detectedvisibly/ audibly, using sensitive listening devices/electronic sensors

Vacuum : Detects leaks visibly when immersedin fluid or by specialized electronic vacuumsensor or gauge with vacuum-decay instrument.


4/34

When to use Pneumatic(air) pressure

test?

Pneumatic tests can be performed only

when the following conditions exist

1) When pressure systems are so designed

that they cannot be filled with water

2) When pressure systems are to be used

in services where traces of the testing

medium cannot be tolerated.


5/34

Main purpose of Pneumatic

pressure testing :

The main reasons are to verify

1) system integrity / strength

2) leak tightness

The objective is to check whether there are

leaks in the welds of the reinforcement platesto shell plates and pontoon of the floating

roof.


6/34

Pneumatic Test Procedure (PTP)

Design survey will review and register

PTP if

1. P>315 psi or

2. V>0.5 m3or

3. Company doesnt have standard PTP included

in their quality program and system p


7/34

Regulations for pneumatic air

testing All pressure piping leak tests must be conducted

using the hydrostatic pressure.

It must be accepted that for a specific pressure

piping system, alternative tests are allowed in acode or standard that is declared.

A pressure piping system shall not be tested at atemperaturethat is colder than its minimum

design temperature. During testing, D-B transition and the possibility

of brittle fracture also needs to be taken intoconsideration


8/34

Risks involved in the process

Air / gas used for pneumatic test is compressible tolarge extent and has very high potential energy storedwhen compressed.

Any minor leak path can lead to a rupture and blastwithin no time releasing total energy with an impact ofsudden explosion.

Time gap between identifying a leakage and failure isvery small making it almost impossible to take remedialaction.

Damages associated with failure are uncontrollableand huge.


9/34

Failure of Pneumatic testing

A incident in

Brazil during

pneumatictesting of

piping, leading

to uprooting

of the tank

above.


10/34

Dangers associated with Pneumatic

Testing

A blown joint A pressure vessel after failure


11/34

Primary concerns

Pressure waves generated

Flying debris


12/34

PRESSURE WAVE :

Depending on the intensity of pressure presentinside the vessel, damage takes place ranging fromgeneration of very loud noise, sonic boom glassfailure to such a max limit that a steel framebuilding can get distorted and pulled from itsfoundation.

FLYING DEBRIS:

Can be classified into1. Primary fragments

2. Secondary fragments


13/34

Pneumatic Test Procedure must

Provide technical justification for notcompleting the hydrostatic pressure test.

Provide a written test procedure that will

fully address the technical and safetyconsiderations for the test.

Be acceptable to the owner. The owner ofthe piping system must review the

circumstances and decide to accept therisk of not hydrostatically testing thepiping system


14/34

Limitations

Stored energy value < 1677 kJ

Pressure piping system is made of P1 or

P8 materials.

Test medium is air or nitrogen

Tests conducted at temp above minimum

design temperature. NOT at a lower

temperature

Tests run under specified set of

conditions only for safe operation.


15/34

Hydraulic Pressure Testing


16/34

Hydrostatic Tests

A hydrostatic test is a test whichmeasures the strength or structuralintegrity of pressurized containers that

hold a liquid or gas.Hydrostatic testing is universally known

and accepted as a means ofdemonstrating the fitness of a pressurized

component for service.It is used to test components for leaks by

pressurizing them inside with a liquid.


17/34

Hydrostatic testing is also requiredperiodically to re-qualify pressure vessels forcontinued service.

The testing method can be used on piping,tanks, valves and containers with welded orfitted sections.

A highly beneficial aspect of hydrostatic testingis it can be used for a new component to beplaced in service for the first time. A similarbenefit accrues to an in-service component ifthat component is taken out of service after aperiod of time and subjected to a hydrostatictest.


18/34

Testing Procedure

Pressure drop procedureIt is used to measure the total systemleakage.

Visual InspectionIt is used in enhancing the visibility ofleakage


19/34

The test involves filling the vessel or pipe

system with a liquid, usually water, which maybe dyed to aid in visual leak detection, and

pressurization of the vessel to the specified

test pressure.

Pressure tightness can be tested by shutting

off the supply valve and observing whether

there is a pressure loss.

The location of a leak can be visually identified

more easily if the water contains a colorant.


20/34

Strength is usually tested by measuring

permanent deformation of the container.

The pressure used in hydrostatic pressure

testing is always considerably more than the

operating pressure to give the customer a

margin for safety.

Typically the test is performed at 150 percent

of the design or working pressure.


21/34

Hydrostatic Leak Testing Standards

1. Standard Method for Hydrostatic Testing

2. ASTM Standard # E1003-95 available from

the ASTM3. American Gas & Chemical Co. Ltd
http://www.amgas.com/gloss.htmhttp://www.amgas.com/gloss.htmhttp://www.amgas.com/gloss.htm


22/34

Limitations of hydrostatic testing

Very costlyPipeline must be out of service for a

period of time

Time out of service hard to predictWater acquisition and disposal costs and

problems

Water hard to remove entirelyDefects too small to fail remain

unidentified and may grow to failure later


23/34

Hydrostatic Testing on Pressure

Vessels The pressure vessel is placed inside a closed

system and a specified internal waterpressure is applied to the container insidethis closed system.

The total and permanent expansion that thecontainer undergoes is measured.

These measurements, along with an internal

and external visual inspection of thecontainer, are used to determine if apressure vessel is safe for continued use ornot.


24/34

Water jacket test for pressure

vessel


25/34

Hydrostatic testing on piping

material Longitudinally oriented defects in pipe

materials have unique failure pressure levels.

The higher the test pressure, the smaller will

be the defects, if any, that survive the test.

With increasing pressure, defects in a typical

line-pipe material begin to grow by ductile

tearing prior to failure.

The purpose is to either eliminate any defectthat might threaten its ability to sustain its

maximum operating pressure or to show that

none exists


26/34

Hydrostatic testing of Plate Heat

ExchangersA minor tube joint leak in a heat

exchanger presents no hazard, whereasleakage of a volatile, flammable orexplosive fluid could cause damage suchas wire drawing, injury or death.

It is necessary to understand the serviceof the exchanger and the degree of

hazard to determine whether to requirethe Manufacturer to perform leak tests.


27/34

Frequency of Testing

Most countries have legislation or buildingcode that requires pressure vessels to be regularlytested.

For example, every two years for high pressuregas cylinders and every five or ten years for lowerpressure ones such as used in fire extinguishers.

Gas cylinders which fail are normally destroyed aspart of the testing protocol to avoid the dangersinherent in them being subsequently used.


28/34

Test Mediums Recommended that the test be conducted in

water.

Liquid hydrocarbons with a flashpoint greaterthan 60 degrees centigrade can also be used asthe test medium.

Typically expand more due to temperature changes

than does water, and it may be more difficult to obtainsatisfactory test results.

For pipelines over water or submerged the productmay spill into the water if a leak occurs during the test.


29/34

Test Segments

Recommended that a pipeline undergoing test

be segmented so that the test is conducted

against blind flanges.

Eliminates the chances of fluid bypass through

valves, which reduces the accuracy of theresults.


30/34

Factors involved

DV/DP calculations: DV/DP : the change in volume for an associated chang

in pressure of a known volume under pressure.

Two DV/DP calculations are used: a theoretical and a

field value.

Fluid Temperature:

Affected by a variety of factors including ambienttemperature, weather conditions, pipe location, testmedia source, pipe color, etc.

As fluid temperature increases, the hydrotest pressurshould be expected to increase.


31/34

Entrained Air:

Entrained air may prevent stabilization of thetesting fluid during a test or may mask the

presence of an actual leak.

expanding air may prevent the detection of anactual leak in the test segment.

Coefficient of Thermal Expansion:

Mediums with high thermal coefficients arevery sensitive to changes in temperature.


32/34

Ambient Conditions

Hydrostatic tests should not be conducted inrainy or wet conditions since visual leakdetection may not be possible.

Aboveground pipe tests should be conducted oncloudy, overcast or cool days to minimize thermalheating of the fluid

Weather/external conditions that should beavoided are very hot (summer), extremely windy,rainy and wet (due to condensate, dew, mist, salt

water spray etc.) conditions.


33/34

Reasons why Hydrostatic test is

safer than Pneumatic test

Liquid used for pressure test are not

compressible as compared to gas.

Energy stored is very less.

Small leak will reduce gauge pressure

immediately which doesnt happen when air is

the test medium.

Leakages are easy to detect in case of

Hydrostatic test.


34/34

Hydrostatic Test Pneumatic Test

1. Recommended for high pressure

applications.

1. Recommended for low pressure

applications.

2. Test media is incompressible,

normally water is used .

2. Test media is compressible, normally

air, Nitrogen, Argon is used.

3. Energy stored per unit volume is

negligible.

3. Energy stored per unit volume is

very high.

4. Difficult to clean after test. 4. Easy to clean after test.

5. Chances of equipment failure are

less.

5. Chances of equipment failure are

high.6. Test media can be reused. 6. Test media cannot be reused.

7. Large lengths can be tested at the

same time.

7. Small segmental lengths tested at a

time.

air and hydraulic tests

Documents