Pressure Testing Safe Practices & Procedure | Safety Checklist

Table of Contents

1.	Purpose
2.	Scope
3.	Definitions
4.	Summary
5.	Procedure
6.	Related Information

 

Appendix A	Safety Distances for Pressure Tests of Piping Systems
Appendix B	Equipment Safety Distance
Table A	Minimum Safe Distance for Piping Based Upon Blast Overpressure
Table A-1 Table A-2	Piping Pressure Test Safety Distances for Persons Outdoors – 70 mbar overpressure Piping Pressure Test Safety Distances for Persons Outdoors – Small Pipe – 70 mbar overpressure
Table A-3	Piping Pressure Test Safety Distances for Persons Inside Nearby Buildings – 50 mbar overpressure
Table A-4	Piping Pressure Test Safety Distances for Persons Inside Nearby Buildings- Small pipe – 50 mbar overpressure
Table B	Minimum Safe Distance Based Upon Pipe Whip
Table B-1 Table B-2	Equipment Pressure Test Safety Distances for Persons Outdoors – 70 mbaroverpressure Equipment Pressure Test Safety Distances for Persons Indoors – 50 mbar overpressure

1. PURPOSE

This procedure defines safe work practices to be followed when conducting system pressure tests.

2. SCOPE

2.1       This procedure applies to pressure testing carried out outdoors at

• Company construction sites.
• Company operating plants.
• Company owned equipment leased to customers where Company has responsibility to install, maintain or repair the equipment (“customer stations”). following installation work or plant or equipment modification or repair.

2.2        Pressure testing at Company Equipment Manufacturing locations is excluded. These facilities have their own pressure test procedures, relating to pressure testing of large vessels and process equipment, carried out indoors, or in pressure test bunkers, etc.

2.3        When Company provides services to its customers that requires pressure testing to be conducted and organized by Company employees, the agreement or contract with the customer shall include provisions for following Company pressure testing practices. Otherwise, Company employees shall not conduct such operations at customer sites.

2.4        This safety requirements of this procedure are intended to apply to strength pressure tests as defined in Section 3, except where leak testing is specifically referred to in the procedure.

2.5       If a system is comprised of parts that routinely get disassembled, such as hose or pigtail end fittings or connectors, clamps, flanges with gaskets, etc., leak testing as defined in Section 3 is carried out after the parts are reassembled and before putting the system back into service. The integrity of the joints made is ensured by leak testing, and a strength test conducted in accordance with this procedure is not required.

3. DEFINITIONS

3.1       Strength Pressure Test

3.1.1     A pressure test undertaken at a pressure above the vessel or system maximum allowable working pressure (MAWP) or design pressure. The purpose is to expose the vessel or system to stresses above those that will be experienced in normal operation, and hence a successful strength test provides assurance of the inherent integrity of the welds and/or brazed joints and onnections on the vessel or system. The strength test can be pneumatic (using a gas or compressed air) or hydraulic (using a liquid such as water).

3.2       Leak Test

3.2.1    A test undertaken at a pressure at or below the system maximum allowable working pressure (MAWP) or design pressure, usually using a gas or compressed air. The purpose is to detect leaks on the vessel connections or on piping connections such as flanges, screwed joints, unions, compression fittings, and at valve glands or other equipment joints to allow the leaks to be repaired before the vessel or system is put into service. Soapy water, leak detection fluids or more sophisticated equipment such as helium leak detectors can be used to find the leaks. Leak testing is often carried out as the pressure in the system is built up, prior to carrying out the strength test.

4. SUMMARY

4.1        Construction pressure testing procedures, customer station pressure testing procedures, facility maintenance pressure testing procedures or project specific pressure testing procedures shall take into account the safe practices outlined in this procedure. Individual test procedures will specify the strength and leak test pressure values and the scope of the circuit under test and other pertinent details of the pressure test set-up. The test pressure values will vary depending on the testing medium, new construction or in-service testing, regulatory requirements, industry codes of practice and local practice.

5. PROCEDURE

5.1       Preparation and Location of Personnel During Testing

• Areas where strength pressure testing is taking place must be considered off-limits for all personnel, except those assigned to perform the work. An area must be roped off as per Appendices A and B around the process equipment or piping system being tested, and applicable warning signs must be posted. If possible, strength pressure tests shall be scheduled for off-shifts to minimize personnel exposure to pressure hazards. The area must be cleared when the testing begins.
• The hazards of strength pressure testing are different to persons indoors, compared to persons outdoors. Pipe or equipment rupture creates the hazard of blast injury to the human body when the person is outdoors. When the person is indoors, the rupture can cause structural damage which could result in the collapse of roof or walls onto people indoors. Hence safe overpressure limits are different. Tables of safe distances are provided in Appendices A and B for persons out-of-doors (70 mbar) and persons in nearby buildings (50 mbar). If there is a building within the 50 mbar safe distance minimum for a test, the building must be evacuated during strength pressure testing.
• Personnel who are involved in the strength pressure testing must be at a safe distance from the equipment while it is being pressurized. Strength pressure tests must never be left unattended when equipment is being pressurized.
• During pneumatic strength pressure testing, personnel should be located out of direct line of site from the equipment under test.
• Personnel who are involved in the strength pressure testing must never stand in line with pipe caps, plugs, or blinds which can blow loose from equipment maintained at pressure.
• Personnel should be sure that fittings, valves, test gauges, and piping for the strength pressure testing hookup are suitable for the test pressure involved.
• Before pressurizing circuits, the whole system to be tested must be inspected to ensure that it is ready and safe to test and it must be verified that all valves are set properly, and the location of vent valves are known in the event that quick venting is necessary.
• A pressure gauge of suitable range must be available on the system at the pressure inlet line. The gauges must be in calibration as defined in local procedures.
• The pressure gauges must be visible to the operator when pressurizing equipment or circuit.

In cases where the operator cannot see a gauge, a second person can be stationed to observe the gauge and relay the information to the pressure test operator.

5.2.1     Whenever practical and possible, hydrostatic strength pressure testing must be used in preference to pneumatic strength pressure testing. While hydrostatic testing is generally safer than pneumatic testing, it is not always feasible, particularly for piped plant systems or for cryogenic systems. If dry out is essential, as in cases where water residue would cause operating problems, then pneumatic testing is preferred.

• Hydrostatic testing using water must use a source of water that is clean and filtered. For stainless steel or equivalent lines or equipment, the chlorine content of the water must not exceed 50 ppm to avoid problems of corrosion.
• Equipment that is undergoing hydrostatic testing must be fitted with suitable drains to permit removal of water after testing.
• Equipment may have to be dried out after testing to remove water remaining in dead-ended cavities or circuits.
• Corrosion effects of residual water remaining in the equipment must be considered when planning hydrostatic tests.
• All piping must be adequately supported during pressure test. Additional supports may be necessary because of the weight of the test fluid. Care must be taken to avoid overloading any supporting structure during pressure test. Spring supports must be blocked to prevent movement prior to pressure testing. For equipment, the foundations must be capable of withstanding the weight of the equipment full of water—calculations may be necessary.
• Hydrostatic tests must not be carried out at a temperature of 2°C (35°F) or less, or the air ambient temperature is 5°C (40°F) and falling. When conducting tests at temperatures below 10°C (50°F), the possibility of a brittle fracture must be considered.
• Hydrostatic testing should not be carried out during periods of rain or fog, unless under suitable cover, as resulting surface moisture may allow small amounts of leaking test liquid to go undetected.
• Where it may be necessary to leave a large system partially filled (not pressurized) with liquid overnight, and low temperatures are likely, a suitable antifreeze must be added to the test liquid. Before being used, the compatibility of the antifreeze with all materials in the system must be evaluated.
• When carrying out hydrostatic tests, care must be taken to ensure that all air is expelled from the system prior to pressure being applied.

5.3       Pneumatic Testing

• A regulator must always be used when pressurizing lower pressure circuits with high pressure cylinders or other sources with pressures higher than the circuit or equipment being tested.
• Dry, clean, and oil-free fittings and lines must always be used when pressurizing oxygen circuits. The pressurizing gas (nitrogen or air) must be dry, oil-free, and filtered.
• When nitrogen or helium is used as a test medium, care must be taken to provide adequate ventilation as leaks may create an asphyxiating atmosphere. Oxygen, carbon dioxide, flammable and toxic gases must not be used.

5.4       Pressure Relief Devices

• All system relief valves, burst discs, and in-line instruments must be either removed or adequately isolated prior to strength pressure test and a test pressure relief device must be installed in the test circuit. In the case of the proven full-flow PSV or thermal PSV set at the design pressure these must be either removed, gagged, or isolated and then replaced with the test pressure relief device.
• However, these needs will be dependent on the actual test pressure value being applied and where necessary as agreed with the governing/regulatory organization. For example, in the USA, established industry practice for existing in-service piped-up systems generally permit leak testing following repairs/alterations to be conducted at 90% of the circuit’s safety device set pressure. This eliminates the need to remove/isolate the items as listed in the above paragraph.
• Test relief devices for hydrostatic and pneumatic strength test, with a set pressure of no more than 10% above the test pressure (reference: ASME B31.3), must be installed. The test relief device and discharge piping must be positioned so as not to cause injury or damage to equipment during discharge, and be adequately supported to accommodate the reaction forces due to discharge. Temporary supports of adequate strength may be needed. Circuits must never be strength pressure tested without an appropriate flow pressure relieving device installed (such as a relief valve or rupture disc) as an integral part of the circuit or equipment.
• The pressure relief device must be sized for the maximum media supply available from the high-pressure media source used for the test. The sizing of the pressure testing relief device must be based on the piping resistance and the wide-open resistance of any regulator, control valve, or manual valves between the pressure source and the test circuit.
• The pressure test relief device must be connected directly to the equipment and not be isolated by valves or blinds.
• Pressure test rigs incorporating an adjustable back pressure vent regulator may be used for strength pressure testing piping only. This is allowed to avoid the need to stock a large number of test relief valves.
• The rig must be used in conjunction with an overpressure protection relief valve sized and set to protect the piping being tested from exposure to a maximum overpressure of 1.8 x Design Pressure, (based on FAR analysis using the 2S205 Overpressure Protection Tool).

• This test rig must have block and bleed valves to enable set-up and testing of the back pressure regulator to ensure that it relieves at a maximum of 1.1 x test pressure by verification against a calibrated pressure gauge. This set-up/calibration must be performed before each pressure test, with the rig isolated from the system under test, and the test results must be documented on the pressure test certificate.

5.5       Pressure Testing Procedure

• Pressure in the equipment must be built up gradually. It is recommended that the pressure be raised in stages. Each stage of pressurization should be a fraction of the design pressure of the equipment. The first stage should be 10% of the MAWP or 2 bar (25 psig), whichever is lower. Once pressure has equalized, personnel may enter the area to check for leaks. If leaks are detected, the system must be depressurized before repairs to the leaking connection are conducted. Any joints or flanges should be soap checked to ensure that connections or isolation points are maintained in sound condition during the pressure test. The pressure must be increased in increments of 10% of the full system strength test pressure value to provide sufficient time to allow the piping to equalize strains during testing, until the desired test pressure is reached.
• The system must be maintained at the “full strength test pressure” for a minimum of ten minutes.
• The pressure should be reduced by 10% from the “strength test” pressure and held at this pressure until all joints have been tested for leaks. If any joint fails to meet acceptance criteria, the system must be depressurized before repairs are carried out. Once all leaks have been repaired, the system must be strength tested again.
• Once the system being tested has been accepted the pressure shall be released slowly at increments of 10% of the pressure test value until depleted.
• Caution must be used when venting accumulated gas from the system. All personnel must be clear of the area and all gas vent piping and lines must be anchored to prevent “whipping”. Whenever possible, gas must be vented upward, rather than horizontally outward to avoid impingement on personnel or adjacent equipment.
• Hearing protection should be used to protect personnel against the high noise levels created while venting down equipment.

5.6       Equipment “Held” Under Pressure

5.6.1     In rare instances that a circuit is to be left pressurized for a “hold test” either overnight or past a shift change, all personnel must be warned at change of shifts of the equipment status. The pressure test conditions and the equipment isolation/preparation requirements must be noted in the site log or night-order book, and signs must be posted around the pressurized equipment reading, “Danger—Equipment Under Pressure,” in conspicuous locations. Isolation valves must be chained or locked closed and tagged with “Danger” tags. The area must be chained or roped off to prevent entry or worker exposure to the pressurized equipment during testing. Hourly checks must be made by qualified persons to inspect the equipment and guard against overpressure because of ambient temperature increases.

5.7       Testing of Transmission Pipelines and Equipment

5.7.1     Testing of transmission pipelines and equipment must be done according to governing organizations, that is, ASME, DOT, etc., and treated on a case-by-case basis.

5.8       System Isolation

• Where the system to be tested ties into any system of a lower design pressure, the lower test pressure system must be either opened to the atmosphere or have appropriate overpressure relief protection to avoid accidental over-pressurization caused by leakage, component failure, etc. Alternatively, spectacle blinds could be added to achieve complete isolation of the low-pressure circuit.
• Valves used to isolate a pressure system or to protect a system from over-pressurization must be locked into position and suitable warning signs attached in accordance with 25-010530 and 25-010532.
• Precautions shall be taken to ensure that any control valves used to isolate a pneumatic test from a lower pressure system cannot be opened, either manually, remotely, or automatically, during the test. Fail-open control valves require special attention to ensure that the fail-open mechanism is deactivated.

5.9       New Construction

• For all new construction relative to piping systems and equipment, the strength pressure testing shall be in compliance with the appropriate local legislation and code requirements.

5.10     In-Service Equipment

• In instances where existing (in-service) equipment must be subjected to pressure testing due to associated system modifications (piping modifications, tie-ins, etc.), the test pressure shall be in accordance with code, jurisdictional and contractual requirements.
• Unless otherwise agreed the test pressure shall not be less than 90% of the circuit relief valve setting. In cases where no circuit relief device exists, the system test pressure shall not exceed 90% of the original test pressure of the equipment, modified to take corrosion into account, if necessary. Test pressures for altered or repaired (in-service) equipment shall be determined by the responsible Pressure Vessel engineer.
• Care should be taken that the weight of the test medium will not overload vessel supports or foundations.

• If the system to be pneumatically tested includes pressurizing equipment and piping, the safety distance shall be the greater of the distances defined for the piping and equipment.

5.11     In-Service Piping Systems

• All pre-spooled piping relative to plant modifications and additions shall be strength tested according to the local legislation and code requirements, that is, ASME, ANSI, Pressure Equipment Directive (PED), etc. and treated on a case-by-case basis.
• The testing requirements for final tie-ins of any pre-spooled piping to the existing plant system shall be as agreed with the pressure system engineer and governing organization (as required). In certain circumstances the pressure testing tie-in welds may be replaced by non-destructive testing providing the equivalent level of safety. As a minimum a leak test shall be performed of the tie-in joints at not less than 90% of the circuit’s safety device set pressure.

5.12     Records

5.12.1  The results of the pressure test inspection findings and details of any repairs made must be recorded in accordance with requirements of group and/or local procedures.

5.13     Qualification of Personnel

• Personnel involved in organizing, setting up and conduction pressure testing must be trained in the appropriate construction pressure testing procedures, customer station pressure testing procedures, facility maintenance pressure testing procedures or project specific pressure testing procedures. The relevant Construction, Engineering, Facility or Project Manager shall determine the competency of the test personnel, based on the training received, previous experience and the degree of experienced supervision available.

6. RELATED INFORMATION

6.1       Company EH&S Documents

25-010530           Safety Work Permit

25-010532           Energy Isolation and Lockout/Tagout/Try

6.2       Process Safety Analysis Methods Manual

PSAM-3.01          Analysis of Explosions

PSAM-5.02          Analysis Method for Siting and Design of Occupied Buildings for Explosion Risk

6.3       Basic Engineering Practice

28-2S205             Hazardous Overpressure Protection

Appendix A

Safety Distances for Pressure Tests of Piping Systems

Because of the potential hazards involved in hydrostatic tests over 25 bar (350 psig), and pneumatic tests over 2 bar (30 psig), personnel shall be kept to an absolute minimum in the immediate area of the test circuit and the injection manifold.

Hydrostatic Pressure Test

For hydrostatic tests above 25 bar (350 psig), the cordoned-off area shall be a minimum distance of 5 m (15 ft) from the circuit under test.

Pneumatic Pressure Test

For pneumatic testing of piping the minimum safe separation distance is given by the larger of the two distances provided in Tables A and B below.

Table A was constructed using the calculation methodology described in PSAM-3.01 PV Explosion and BLEVE Analysis and the DNV consequence analysis software PHAST. The blast height assumed was 1.5 m, as was the subject (person) impact height. The blast source was assumed to be cylindrical.

When using Table A, the total pipe length should be the total straightened-out length of the pipe and fittings that will be under the pneumatic test. If the piping to be tested includes sections of different diameter, the largest diameter should be used in employing Table A.

Table B was constructed to account for the consequences of whip of the failed piping. The total pipe length should be the total straightened-out length of the pipe and fittings that will be under the pneumatic test. If there are multiple constraint points along the length of a pipe, the total length is the straightened out length of the longest segment between constraints.

Table A

Minimum Safe Distance for Piping Based Upon Blast Overpressure

Table A-1

Piping Pressure Test Safety Distances for Persons Outdoors – 70 mbar overpressure

Table A-2

Piping Pressure Test Safety Distances for Persons Outdoors – Small Pipe – 70 mbar overpressure

 

Table A-3

Piping Pressure Test Safety Distances for Persons Inside Nearby Buildings – 50 mbar overpressure

 

 

Table A-4

Piping Pressure Test Safety Distances for Persons Inside Nearby Buildings- Small pipe – 50 mbar overpressure

Table B

Minimum Safe Distance Based Upon Pipe Whip

Total Pipe Length with Minimum of one End Adequately Constrained, meters (ft.)	x 1.5	=	Minimum Safe Distance, meters (ft.)
Total Pipe Length with Neither End Adequately Constrained, meters (ft.)	x 2.0	=	Minimum Safe Distance, meters (ft.)

 

• Equipment nozzles and pipe guides which restrict motion in at least two dimensions are considered to provide adequate constraint. Pipe rests do not provide adequate constraint.
• Every effort should be made to place at least one constraint on a pipe being tested. If a single constraint is used, it should be placed near the center point of the pipe.

Appendix B Equipment Safety Distance

The safety distance to persons outdoors for a pneumatic test of equipment shall be determined from the table below:

Table B-1

Equipment Pressure Test Safety Distances for Persons Outdoors – 70 mbar overpressure

The safety distance to the nearest part of a building for a pneumatic test of equipment shall be determined from the table below:  If there is a building within this distance, it must be evacuated during pressure testing.

Table B-2

Equipment Pressure Test Safety Distances for Persons Indoors – 50 mbar overpressure

[The tables were constructed using the calculation methodology described in PSAM – 3.01 PV Explosion and BLEVE Analysis and the DNV consequence analysis software PHAST. The assumptions are the same as noted with Table A in Appendix A. Shrapnel was not considered.]

Hydraulic Test

For hydraulic tests of pressure vessels the safety distance shall be 10 m (33 ft).