Pressure Testing of Corroded Piping 3

[Sarahm554]

Deal All,

I had discussion with an Inspection Engineer of oil and gas plant and He has raised a query that pressure testing of corroded/old piping shall not be carried out at 150% of design pressure. My point of view is that, as far as, minimum required thickness is still available then pressure testing should be done at 150% of design pressure. This minimum required thickness also considers all other loading's apart from pressure design thickness.

can anyone guide on this matter.

Thanks in advance

 

[john ambrose]

Pressure Testing is a non-destructive test performed to ensure the integrity of the pressure shell on new pressure equipment, or on previously installed pressure and piping equipment that has undergone an alteration or repair to its boundary(s).
Pressure testing is required by most piping codes to verify that a new, modified, or repaired piping system is capable of safely withstanding its rated pressure and is leak tight. Compliance to piping codes may be mandated by regulatory and enforcement agencies, insurance carriers, or the terms of the contract for the construction of the system. Pressure testing, whether or not legally required, serves the useful purpose of protecting workers and the public.
Pressure testing may also be used to establish a pressure rating for a component or special system for which it is not possible to establish a safe rating by calculation. A prototype of the component or system is subjected to a gradually increasing pressure until measurable yielding first occurs or, alternatively, to the point of rupture. Then by using derating factors specified in the code, or the standard, appropriate to the component or system, it is possible to establish a design pressure rating from the experimental data.


PIPING CODES
There are a great many codes and standards relating to piping systems. Two codes of major importance for pressure and leak testing are the ASME B31 Pressure Piping Code and the ASME Boiler and Pressure Vessel Code. While these two codes are applicable to many piping systems, other codes or standards may have to be met as required by the authorities, insurance companies, or the owner of the system. Examples might be AWWA standards for water transmission and distribution system piping. The ASME B31 Pressure Piping Code has several sections. They are:
ASME B31.1 for Power Piping
ASME B31.2 for Fuel Gas Piping
ASME B31.3 for Process Piping
ASME B31.4 for Liquid Transportation Systems for Hydrocarbons, Liquid Petroleum Gas, Anhydrous Ammonia, and Alcohols
ASME B31.5 for Refrigeration Piping
ASME B31.8 for Gas Transmission and Distribution Piping Systems
ASME B31.9 for Building Services Piping
ASME B31.11 for Slurry Transportation Piping Systems
The ASME Boiler and Pressure Vessel Code also has several sections which contain pressure and leak testing requirements for piping systems, pressure vessels, and other pressure retaining items. These are:
Section I for Power Boilers
Section III for Nuclear Power Plant Components
Section V for Non Destructive Examination
Section VIII for Pressure Vessels
Section X for Fiberglass Reinforced Plastic Pressure Vessels
Section XI for In Service Inspection of Nuclear Power Plant Components
There is great similarity with respect to the requirements and procedures for testing among the many codes. Various leak-testing methods, planning, preparation, execution, documentation, and acceptance standards for pressure testing will be discussed in this chapter. Equipment, useful for pressure testing, will also be included in the discussion. The material that follows should not be considered a substitute for a complete knowledge or careful study of the particular code requirement that must be used to test a particular piping system.

 

[Sarahm554]

API-570 states that whenever pressure testing of in-service piping is required, then it shall be performed in accordance with the requirements of ASME B31.3. Additional consideration are also provided by ASME-PCC-2. No where it is mentioned that test pressure can be reduced, however it can be exempted based on application of appropriate NDT methods when a pressure test is not performed after a major repair or alteration with necessary approvals.

I will try to conclude that whenever pressure testing of in-service piping is required after a repair or alteration, test pressure shall be in accordance with ASME-B 31.3, API-570, API 574 or ASME-PCC 2 where all these mentioned codes/standards/RP requires a test pressure of 1.5 x design pressure assuming that all piping sections/components meets the minimum required thickness criteria. Minimum design wall thickness results from applying the allowable stress criteria to design pressure and temperature, while superimposing all the other possible loading conditions, wind, seismic, hydrodynamic, etc. If any section/component of piping does not meet the minimum required thickness criteria then pressure testing is not allowed unless repair or replacement has been performed to confirm that all piping sections /components are above the minimum required thickness.

Regards
Sarfraz
Have a good day.