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Pressure and Vacuum Systems Safety Supplement Part
6: Pressure and Leak Testing |
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The primary reason for pressure testing is to confirm the integrity of a pressure system. Hydrostatic pressure testing can also provide local relief of mechanical stresses. Pressure testing of new systems or new components poses a potential hazard to both equipment and personnel due to the stored energy of the pressurized fluid. For this reason, only trained and qualified personnel may supervise a pressure test. Pressure or leak tests may require internal pressure, external (i.e. vacuum) pressure or both. This section describes the requirements for pressure and leak testing.
All pressure systems considered new construction shall be tested as required by the Code of Record. This test shall be witnessed by the inspector. Upon agreement of the inspector, the System Owner, and the system DA, the inspector may forego the witness of the final system pressure test. Documentation of this test (Form PS-7) is required and shall be filed in the appropriate file in the Pressure System database.
All personnel directly involved in pressure testing shall meet the requirements of Part 1: Section 1.4.5 Pressure System and Testing Technicians. For pressure systems tested on-site by subcontractors, the DA/SOTR is responsible for ensuring that the contract includes requirements for personnel to be appropriately trained and qualified to perform the work as well as trained in the hazards of pressure if exposed. Training and qualification through the subcontractor is acceptable.
The following Codes and Standards may be applicable to any given pressure or leak test.
· ASME B31 Piping Codes
· ASME BPVC
· ASME PCC2
· NBIC (NB-23)
ASME and National Board Codes require pressure/leak testing for new construction, alterations and repairs. The requirements of the most applicable Code of construction or post construction shall be met. Due to the potential significant hazards associated with pressure testing, the DA or pressure test engineer shall determine the stored energy of components to be tested. The stored energy shall be calculated by any method determined suitable by the DA or pressure test engineer such as those given in Part 6: Section 6.1.4 Stored Energy.
Procedures for leak/pressure testing shall follow ASME B31.3 ¶ 345, ASME BPVC D1 UG-99 through UG-102 or other more applicable Code Section. In general, there are three basic types of pressure tests
· Hydrostatic where the test fluid is liquid
· Pneumatic where the test fluid is a gas
· Hydro-pneumatic where the test fluid is a combination of gas and liquid
Pneumatic and hydro-pneumatic testing shall not be performed on piping systems, vessels, or any other components subject to brittle fracture such as glass, PVC, CPVC, cast iron, etc. Pneumatic pressure testing of special use components (e.g. target cells) fabricated from such material is allowed under an OSP or TOSP.
Although the stored energy of pneumatic tests is typically much larger, they may be more appropriate in certain conditions. Where a hydrostatic or hydro-pneumatic test may damage lining or insulation, overstress the system or supports due to test fluid weight, or contaminate the process, a pneumatic test may be more suitable. This may also be true if the test temperature of a hydrostatic or hydro-pneumatic test could lead to brittle fracture.
Leak testing vacuum equipment or pressure components evacuated for leak testing with both a cross sectional area larger than 33 in2 and a volume greater than 35 ft3 shall follow the process steps given in Part 6: Section 6.1.3 Process Steps. When a sensitive leak test is performed, it shall be considered a pneumatic test and the process steps of Part 6: Section 6.1.3 Process Steps shall be followed.
The following process steps shall be used to perform leak/pressure tests
1. Determine the scope and nature of the pressure test. Ensure that both Code and Jefferson Lab requirements will be met.
2. Determine the stored energy of the test.
3. An OSP or TOSP shall be prepared if any of the following conditions exist.
o The mechanical stored energy of the test is greater than 73756 ft-lb (100 kJ)
o Any component to be tested was exposed to a Category “M” fluid as described in ASME B31.3 and has not been fully cleaned and released
o The test fluid is not inert (i.e. water, nitrogen, helium, etc.)
o The test fluid is air and the test pressure is greater than 250 psi
o The test must be performed on a radioactively contaminated system
4. The OSP or TOSP, if required, must describe the following in detail
o Roles and Responsibilities
o Rational for selection of test type
o Stored energy of test
o Qualifications of personnel performing the test
o Protection for personnel performing the test
o Protection for personnel near or potentially exposed to the test area
o Protection for equipment
o Description of system and extent of tested components
o Test rig or pressure manifold
o Schematic of the test instrumentation, relief valves, and tested system
o Possible ODH hazards
o Detailed procedure for performing the test competent
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o Inspection prior to, during, and after test
o Recovery procedures if applicable
5. A pressure test form (Form PS-7) shall be completed by the test engineer, test technician, and Owner’s Inspector if applicable.
6. The DA shall ensure that the pressure test form is filed in the Pressure Systems database.
The stored mechanical energy of the test volume may be calculated using several methods. These methods include the following:
· Ideal Gas Laws
· Brode equation for stored energy of a gaseous volume
· Baker equation for stored energy of a gaseous volume (given below)
· Aslonov-Golinsky equation for stored energy of a gaseous volume
· Enthalpy tables
· Equation for stored energy of liquid
The DA shall determine the method most appropriate for determining the stored energy of the test volume. The DA or test technician performing the calculation is cautioned to ensure consistency with units. If the system fluid is reactive, flammable, or explosive, the chemical potential energy must also be determined. The stored energy of a pressurized fluid that is flammable or explosive is thus the sum of the chemical as well as mechanical stored energies.
The stored mechanical energy of a gas may be calculated using the following expression
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E
= |
PtestV |
[1–( |
Patm |
) |
(k-1)/k |
] |
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k-1 |
Ptest |
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Where:
E = stored energy of test
V = test volume
Patm = absolute atmospheric pressure of test (14.7 psia in US cust. units)
Ptest = absolute pressure of test
K = Ratio fo specific heats
Note: any system of units may be used (e.g. ASME PCC-2 Article 5.1) provided that they are consistent.
The stored mechanical energy may be converted to an equivalent mass of TNT. The following equation may be used to convert the stored energy of a system to pounds of TNT:
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TNT = |
E |
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1488617 |
Where:
E = stored energy of test (ft-lbf)
TNT = equivalent amount of TNT (lb)
Note: alternate units may be used (e.g. ASME PCC-2 Article 5.1) provided that they are consistent.
The stored mechanical energy of a liquid that does not boil at ambient pressure and temperature may be calculated using the following equation:
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E = |
V |
[ |
yP |
– ln(1+ yP) |
] |
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y |
1+ yP |
Where:
E = stored energy of test
V = test volume
P = test pressure
Y = compressibility of fluid
The compressibility of water at 10,000 psi is 2.7 X 10-6 psi-1. Similar fluids have compressibilities of the same order of magnitude. Thus, in many cases of moderate pressure, a good approximation of the stored energy is:
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E
= |
VyP2 |
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2 |
This expression should only be used for conditions where
The stored energy within a vacuum vessel may be approximated with the following equation using US customary units:
E = 144in2/ft2(Patm)(V)
Where
E = stored energy of test (ft-lbf)
Patm
= absolute atmospheric
pressure of test (14.7 psia in US customary units)
V = test volume (in cubic feet)
Note: alternate units may be used (e.g. ASME PCC-2 Article 5.1) provided that they are consistent.
The minimum safe distance between personnel and the equipment being tested shall be the greater of 3 ft. and R which is determined by the following equation:
R = Rs(TNT)1/3
Where:
Rs = scaled consequence
factor 50 ft/lb1/3
TNT = stored energy in lb of TNT
R = required minimum distance for personnel
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ISSUING AUTHORITY |
SUPPLEMENT AUTHOR |
APPROVAL DATE |
REVIEW DATE |
REV. |
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QA/CI Dept. |
11/06/15 |
11/06/20 |
1.0 |
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