Pressure testing

Obj 1 - identify equipment fir pressure test piping installs

• 2 types of testing

  • Hydrostatic:

    • most popular by far- because water is virtually incompressible

      • If large volumes of pipe, you would need alot of air

      • Relieving air pressure would also take long

      • Lowers chance of explosive release of gas from pipe

      • Hydro test leaks are easier to find

    • Not limited to water, can be mixture

      • may need separate drain and fill connections to prevent environmental damage. Or spill pans.

    • Require vents at all high points and drains at all low points.

  • Pneumatic:

    • some lines require no moisture or liquid at any time.

    • Or too costly to bring a water truck on site

    • Air normally has high moisture- air must be dried otherwise you may use nitrogen or CO2.

    • Always monitor leak test pressures as ambient temperature swings may increase test pressure beyond maximum allowable.

• Equipment used

  • Pumps/Compressors

    • pump- discharge fluid against pressure

    • Compressor- also a pump but discharges gases against pressure

  • Pump styles for pressure tests:

    • Pump driver

      • hand lever, moves a pneumatic diaphragm, smaller systems

    • Pneumatic diaphragm pump

      • operates direct ratio if input to output pressure. 100:1 can make 3000 psig with 30psi supply pressure

    • Motor driven pump

      • emits CO and CO2 so not typically used indoors or space needs to be ventilated

      • Local environment determines which motor type to use for the job

        • If electric motor: should check if the motor classification is TEXP (totally enclosed explosion proof)

          • Most plants require motor to be connected via GFI on the end of extension cord if the motor cannot be plugged into gfi outlet.

        • If air driven:

          • needs high air pressure. Larger hose. Lubricator installed in line.

          • Ensure all air connections are tight before powering.

    • Air compressor

      • uses a regulator (PRV)

      • Moisture in test air should be removed prior to PRV.

    • Gas cylinders

      • dry gas at very high pressure through a PRV

      • Hose connections are right hand.

        • only oxygen tanks have a CGA 540 thread.

        • Other gasses have a thread based on gas composition

  • Hose and fittings

    • extreme high pressure hose is reinforced with metal or fibre mesh

    • Carbon steel fittings are most commonly used unless fluid conditions require other material.

    • Usually union or quick connects

    • Most pressure hoses are small ID, so a larger diameter fill line sometimes needed to speed up fill time(usually tee that gets capped after)

    • Pressure rating must be equal to or greater than your maximum pump output pressure.

    • High pressure hose is connected from utility air to an air drive motor

      • Connected via universal couplings (chicago, crow coot, claw coupling)

      • Older versions needed saftey pin to prevent accidental twist in use

      • Newer hose may have self lock mechanism

    • Whipcheck can be used to prevent hose from lashing

  • Gauges

    • bourdon tube type

    • Need to be calibrated

    • Accuracy of manual reading increases with dial face

    • If pump skid doesnt have a master gauge and recorder, the gauge attached at the test connection becomes the test gauge, must be on same pipe as recorder.

    • PFI Standard ES-4 states:

      • pressure test gauge must be indicating pressure gauges and be connected directly to piping system if possible

      • Dial on gauge graduated double max test pressure, no less than 1.5 and no more than 4 times.

    • Vibrations:

      • if not severe use oil filled gauge

      • If severe, remote mount

      • Pulsation dampeners (snubber) can be used to prevent pulsation damage

Obj 2 - describe procedure and req for pneumatic and hydro test

• owner’s management or safety code officer determines which code to use in job

• Fabrication company’s QC responsible for performing testing and ensuring standards met

• Codes:

  • ASME B31: fabrication and install of pressure pipe.

  • CSA

  • AWWA

  • National Plumbing Code

  • B149 Gas Install Code

• Inspectors are responsible for ensuring testing is performed and equipment meets/exceeds minimum QC requirement.

• Always consult authority having jurisdiction over test requirement

• Hydrostatic Test

  • usually fulfills code requirement

  • Safer than pneumatic since not much volume spills out (depressurizes quickly)

  • Dangerous during winter time if pipe freezes!

  • Usually 1.5x the max working pressure.

  • Once components are assembled and fastened, pipe code requires a leak test. As per ASME B31.3:

    • before placing in operation, a leak test must be done

    • Test shall be hydrostatic and hold for 10 minutes

    • All joints/connections tested for leaks.

  • ASME B31.3 requires this info:

    • Id of system, assembly being tested

    • Test date

    • Fluid used for hydro test

    • Certification of result by examiner

  • Other things to consider:

    • flag off area when pressure testing

    • Ensure all air removed, it should take very little fluid to pressurize.

    • Pressurize to half pressure and verify for leaks first

    • Record ambient temperature and time when starting test. Ambient temperature swings will greatly change hydro test pressure

    • Increase in small increments to allow pipe stresses to normalize.

• Pneumatic Test

  • air, nitrogen, argon is common

  • Other things to consider:

    • ensure a pressure relief is installed with no more than test pressure + 50 psig OR test pressure plus 10%. Whichever is leasT

    • Flag off area

    • Open valves slow

    • Pressure first to 25 psig or half the test pressure, whichever is less and perform preliminary test before going to full pressure

    • Test to 110% design pressure, when done, reduce to operating pressure. Record time and ambient temp and start pressure test.

  • Documents for pneumatic tests are the dame as hydro, but:

    • If volume is large, a permit from authority having jurisdiction is required. Usually if greater than 0.5 m3 or 18ft3 OR >300 psig test pressure. Oo

    • A engineering calc is needed for total energy compressed. Document to be attached to test documents.

Obj 3 - hazards specific to pressure testing

• safety depends on proper preparation

  • all openings sealed

  • Isolation valve- fill and test piping isolation as close to assembly as possible.

  • Provisions to vent air from system

  • Support system adequate for test fluid and test assembly.

  • If separate fill hose used, add extra fluid through test hose to ensure full before capping last vent.

  • Watch pressure gauge during pump start up,

    • Sharp spike may be a valve is isolated somewhere

    • Slow to increase may indicate air is trapped, open vents and vent out air.

• Compressed gas is much more dangerous than pressurized liquids. Amount of energy can be calculated equivalent to TNT

  • 500ft of 1” pipe at 150psi can be 1.63 ounces of TNT. 2” =8oz TNT, 6”=5lbs TNT