Last year I broke down the pressure and leak test requirements found in ASME B31.5 for those of you in the Ammonia Refrigeration industry, and at the time, I promised I would do the same for those of you that use ASME B31.3 in all the other process industries. And as I got busy with other things, I forgot to follow up until my PSM SeminarFest course this weekend, when a student got access to the website and could not find this information. So here are the pressure and leak testing requirements found in ASME B31.3, our PSM/RMP RAGAGEP for our process piping.
General Requirements for Leak Tests (Section 345)
The test pressure may be reduced to the maximum pressure that will not exceed the piping’s yield strength at the test temperature. If a pressure test is to be maintained for a period of time AND the test fluid being used can expand under the test conditions (including ambient atmospheric conditions, the code requires that precautions be taken to avoid excessive pressure from the thermal expansion.
The code allows for a preliminary “pressure test” using regular air at no more than 25 psig. This preliminary “pressure test” is intended to be done prior to hydrostatic testing to locate any major leaks in the piping circuit being tested. The code calls for the test pressure to be maintained for at least 10 minutes. After successfully completing the pressure test, we can reduce the pressure in the pipe circuit and examine/inspect ALL joints and connections for leaks.
These tests MUST be conducted AFTER any heat treatment has been completed.
We should be alert to the possibility of brittle fracture when conducting leak tests at metal temperatures near the ductile-brittle transition temperature. The final weld connecting piping systems or components that have been successfully tested in accordance with para. 345 need not be leak tested provided the weld is examined in-process in accordance with para. 344.7 and passes with 100% radiographic examination or 100% ultrasonic examination. Piping subject to external pressure shall be tested at an internal gage pressure 1.5 times the external differential pressure but not less than 15 psi.
When we have “jacketed piping”, also sometimes called “double walled” piping, the internal pipe is to be leak tested on the basis of the internal or external design pressure, whichever is critical. This test MUST be performed BEFORE the jacket is completed when it is necessary to provide visual access to joints of the internal line as required by para. 345.3.1. The jacket shall be leak tested on the basis of the jacket design pressure unless otherwise specified in the engineering design.
Repairs or Additions After Leak Testing
If repairs or additions are made following the pressure/leak test, the affected piping shall be retested, except for minor repairs or additions the owner may waive retest requirements when precautionary measures are taken to assure sound construction.
Test Records
Records shall be made of each piping system (e.g. circuits) during the testing, including:
(a) date of test
(b) identification of piping system tested
(c) test fluid
(d) test pressure
(e) certification of results by examiner
NOTE: These records need NOT be retained after completion of the test WHEN A CERTIFICATION by the “Inspector” that the piping has satisfactorily passed pressure testing as required by this Code is retained.
Preparation for Leak/Pressure Testing
All joints, welds (including structural attachment welds to pressure-containing components), and bonds shall be left UNINSULATED AND EXPOSED for examination during testing. Joints previously tested in accordance with this Code may be insulated or covered. In most cases, pipe joints may be primed and/or painted prior to leak testing; unless a sensitive leak test under 345.8 is required. Piping DESIGNED for VAPOR and/or GAS MUST be provided with additional “temporary” supports when needed, when doing hydrostatic testing in order to support the weight of test liquid.
Limits of Tested Piping (345)
Equipment that is not to be tested MUST be either disconnected from the piping or isolated by blinds or other means during the test. A valve may be used provided the valve (including its closure mechanism) is suitable for the test pressure.
HYDROSTATIC TESTING
Hydrostatic Leak Test Test Fluid
The fluid SHALL BE WATER unless there is the possibility of damage due to freezing OR to adverse effects of water on the piping or the process. In the situation where water is NOT used, another suitable NONTOXIC liquid must be used.
If the liquid is flammable (NOT recommended), it’s flash point MUST be >120°F, and consideration shall be given to the test environment. This means that if the pipe being tested runs through an area where the outside temp could be 120°F or hotter, then a flammable liquid that has a FP less than the outside temp MUST be used. The area may also need to be electrically classified (HAZLOC) depending on the amount of flammable used in the area.
Test Pressure
Except as provided in para. 345.4.3, the hydrostatic test pressure at EVERY POINT in a metallic piping system shall be as follows:
(a) not less than 1.5 times the design pressure
(b) when the design temperature is greater than the test temperature, the minimum test pressure, at the point under consideration, shall be calculated using eq.
PT= 1.5 PST / S
where
P = internal design gage pressure
PT = minimum test gage pressure
S = allowable stress at component design temperature for the prevalent pipe material; see Table A-1
ST = allowable stress at test temperature for the prevalent pipe material; see Table A-1
(c) in those cases where the piping system may not include pipe itself, any other component in the piping system, other than pipe-supporting elements and bolting, may be used to determine the ST/S ratio based on the applicable allowable stresses obtained from Table A-1.
In those cases where the piping system may be made up of equivalent lengths of more than one material, the ST/S ratio shall be based on the minimum calculated ratio of the included materials.
(d) if the test pressure as defined above would produce a circumferential pressure or longitudinal stress (based on minimum pipe wall thickness) in excess of the yield strength at test temperature or a pressure more than 1.5 times the component rating at test temperature, the test pressure may be reduced to the maximum pressure that will not exceed the lesser of the yield strength or 1.5 times the component ratings at test temperature.
[See paras. 302.3.2(e) and (f).] For metallic bellows expansion joints, see Appendix X, para. X302.2.3(a).
Hydrostatic Test of Piping With Vessels as a System
Where the test pressure of piping attached to a vessel is the SAME AS OR LESS THAN the test pressure for the vessel, the piping may be tested with the vessel at the piping test pressure.
Where the test pressure of the piping EXCEEDS the vessel test pressure, AND it is not considered “practicable” (not defined in the code) to isolate the piping from the vessel, the piping and the vessel may be tested together at the VESSEL TEST PRESSURE, provided the OWNER APPROVES AND the vessel test pressure is NOT LESS THAN 77% of the piping test pressure calculated in accordance with para. 345.4.2(b).
PNEUMATIC TESTING
Pneumatic Leak Test Precautions
Pneumatic testing involves the hazard of released energy stored in compressed gas. Particular care must, therefore, be taken to minimize the chance of brittle failure during a pneumatic leak test. The test temperature is IMPORTANT in this regard and must be considered when the designer chooses the material of construction.
Pressure Relief Device(s)
A pressure relief device MUST be provided, having a set pressure NOT HIGHER than the “test pressure” plus the lesser of 50 psi or 10% of the test pressure.
Test Fluid
The gas used as test fluid, if not air, shall be NONFLAMMABLE AND NONTOXIC.
Test Pressure
The test pressure shall be not less than 1.1 times the design pressure and shall not exceed the lesser of: (a) 1.33 times the design pressure (b) the pressure that would produce a circumferential pressure or longitudinal stress (based on minimum pipe wall thickness) in excess of 90% of the yield strength of any component at the test temperature
Procedure
The pressure shall be gradually increased until a gage pressure that is the lesser of one half the test pressure or 25 psi is attained, at which time a preliminary check shall be made, including examination of joints in accordance with para. 341.4.1(a). Thereafter, the pressure shall be gradually increased IN STEPS until the test pressure is reached, holding the pressure at EACH STEP long enough to equalize piping strains. The pressure shall then be REDUCED TO THE DESIGN PRESSURE BEFORE examining for leakage in accordance with para. 345.2.2(a).
Hydrostatic-Pneumatic Leak Test
If a COMBINATION hydrostatic-pneumatic leak test is used, the requirements of para. 345.5 shall be met, and the pressure in the liquid filled part of the piping shall not exceed the limits stated in para. 345.4.2.
Initial Service Leak Test
This test is applicable ONLY to piping in Category D Fluid Service, at the owner’s option. See para. 345.1(a).
PLEASE NOTE: CATEGORY D Fluid is NOT flammable, toxic or otherwise harmful to human tissues. Harmful means exposure that can harm skin, eyes or mucous membranes that irreversible damage may result unless immediate action is taken. The Design Gauge pressure is below 150 psi and the Design Temperature is between -20°F to 366°F. An example of Category D fluid might be utility water in a plant or low pressure steam condensate.
Test Fluid
When doing initial service leak testing on Category D fluids, the test fluid is the service fluid. During or prior to initial operation, the pressure shall be gradually increased in steps until the operating pressure is reached, holding the pressure at each step long enough to equalize piping strains. A preliminary check shall be made as described in para. 345.5.5 when the service fluid is a gas or vapor.
Examination for Leaks
The examination for leaks required by para. 345.2.2(a) shall be conducted while the system is at OPERATING PRESSURE. It is permissible to omit examination for leaks of joints and connections previously tested in accordance with this Code.
Sensitive Leak Test
The test shall be the “Bubble Test — Direct Pressure Technique” in accordance with the BPV Code, Section V, Article 10, Appendix I or another leak test method that meets the code required test conditions.
When the Bubble Test — Direct Pressure Technique is used, the test pressure shall be at least the lesser of 15 psig or 25% of the design pressure. The pressure shall be gradually increased until a gage pressure equal to the lesser of one-half the test pressure or 25 psi is attained, at which time a preliminary check shall be made. Then the pressure shall be gradually increased in steps until the test pressure is reached, the pressure being held long enough at each step to equalize piping strains.
Alternative to Leak
The following procedures and leak test method may be used ONLY when the owner considers BOTH hydrostatic and pneumatic leak testing impracticable (not defined or quantified in the code).
Examination of Welds
Welds, including those used in the manufacture of welded pipe and fittings, that have NOT been subjected to hydrostatic or pneumatic leak tests in accordance with this Code, shall be examined as follows:
- Circumferential, longitudinal, and spiral (helical seam) groove welds shall be 100% radiographed in accordance with para. 344.5 or 100% ultrasonically examined in accordance with para. 344.6.
- All welds, including structural attachment welds, not covered in (a) above, shall be examined using the liquid penetrant method (para. 344.4) or, for magnetic materials, the magnetic particle method (para. 344.3).
Flexibility Analysis
A flexibility analysis of the piping system shall have been made in accordance with the requirements of para. 319.4.2 (b), if applicable, or (c) and (d).
Test Method
The system shall be subjected to a sensitive leak test in accordance with para. 345.8.
RECORDS
It is the responsibility of the piping designer, the manufacturer, the fabricator, AND the erector, as applicable, to prepare the records required by this Code and by the engineering design.
Unless otherwise specified by the engineering design, the following records shall be retained for at least five (5) years after the record is generated for the project:
(a) examination procedures
(b) examination personnel qualifications