Download - Air and Hydraulic Tests
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AIR AND HYDRAULIC TESTS
PERFORMED ON PROCESSEQUIPMENTS, ITS
IMPORTANCE ANDLIMITATIONS
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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.
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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.
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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.
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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.
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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
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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
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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.
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Failure of Pneumatic testing
A incident in
Brazil during
pneumatictesting of
piping, leading
to uprooting
of the tank
above.
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Dangers associated with Pneumatic
Testing
A blown joint A pressure vessel after failure
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Primary concerns
Pressure waves generated
Flying debris
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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
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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
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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.
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Hydraulic Pressure Testing
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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.
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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.
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Testing Procedure
Pressure drop procedureIt is used to measure the total systemleakage.
Visual InspectionIt is used in enhancing the visibility ofleakage
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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.
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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.
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Hydrostatic Leak Testing Standards
1. Standard Method for Hydrostatic Testing
2. ASTM Standard # E1003-95 available from
the ASTM3. American Gas & Chemical Co. Ltd
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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
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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.
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Water jacket test for pressure
vessel
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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
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.