Pressure Testing of Corroded Piping
Pressure Testing of Corroded Piping
(OP)
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
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





RE: Pressure Testing of Corroded Piping
RE: Pressure Testing of Corroded Piping
RE: Pressure Testing of Corroded Piping
As far as I am aware (I stress I am not an engineer) 1.5 times design pressure is for new piping.
Again, as far as I am aware there are codes/ standards that deal with piping that has been in service.
My only question would be if it was tested at 1.5 times design pressure when piping was brand new why would you test at the same pressure if it has corroded down to minimum required thickness ?
Regards,
Shane
RE: Pressure Testing of Corroded Piping
RE: Pressure Testing of Corroded Piping
Lets go back to basics here:
Pressure testing to 1.5 times design pressure is included in design codes (B31.3 for example) to demonstrate that a particular piping system is able to perform at that pressure plus a suitable margin to allow for operational loads, expansion etc in service.
It matters not whether this is new piping or old piping.
If you are in essence re-certifying the piping after a repair. If the test results in loss of containment of an older corroded section, then it needs to be replaced or the design pressure lowered to meet the new conditions.
It is not unknown that systems become revised when after a couple of tests, you cant achieve more than a certain pressure without some part of the piping leaking, this pressure being less than 1.5 x design pressure. They then revise the Design pressure down so that it meets the 1.5x requirement.
E.g. You have a design pressure of 800 psi. Your test pressure is then 1200. However you can't get beyond 900 psi in your pressure test. The new design pressure is 600 psi. Only you can decide if you need 800 or whether 600 will do. Up to you and the owner.
Pressure testing is a bit of a blunt tool, but if your system passes then it makes everyone happy - management, lawyers, insurance, etc that you have undertaken what is required by the codes to certify a particular system.
Dekdee - the codes require a certain design thickness. you can add on corrosion allowance to that if required / necessary, but that minimum thickness is required to meet the design pressure. Therefore if you still have that thickness, why wouldn't you test to the same pressure?
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Pressure Testing of Corroded Piping
Thanks for the response.
I was trying to get my head around the difference between design thickness and minimum required thickness.
I thought if piping was fabricated to design thickness and then it had corroded but was still above minimum required thickness that it would have a reduced test pressure ?
I think I will stick to questions about welding - a bit safer for me. LOL !
Cheers,
Shane
RE: Pressure Testing of Corroded Piping
RE: Pressure Testing of Corroded Piping
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. that might be concurrently applied to the design pressure and temperature condition and then adding the corrosion allowance to that. That result is in effect the minimum required wall thickness.
RE: Pressure Testing of Corroded Piping
Can you not isolate the replaced section of piping and test this only with maybe the final weld radiographed (golden weld) with client permission but maybe this is not possible if various sections of the system are replaced?
RE: Pressure Testing of Corroded Piping
surely you mean just minimum thickness as calculated for the design pressure?? The CA is exactly that, an allowance for corrosion so that if it does corrode, the thickness doesn't reduce below the minimum you need for the design pressure.
In many case, depending on the amount of corrosion, its depth, length etc, the pipe is still good for the design pressure, but that's a fitness for purpose assessment which is something different.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Pressure Testing of Corroded Piping
You are correct, I should have phrased better. My intent was that the thickness should be minimum for the design pressure but you would still have an additional CA if required to suit operational life otherwise if down to minimum and corrosion expected it should also be replaced.
RE: Pressure Testing of Corroded Piping
I am a little confused.
Your comment
Pressure testing to 1.5 times design pressure is included in design codes (B31.3 for example) to demonstrate that a particular piping system is able to perform at that pressure plus a suitable margin to allow for operational loads, expansion etc in service.
It matters not whether this is new piping or old piping.
This is from B31.3 and what I based my earlier comments on.
Intent of the Code
(1) It is the intent of this Code to set forth engineering
requirements deemed necessary for safe design
and construction of piping installations.
(2) This Code is not intended to apply to the operation,
examination, inspection, testing, maintenance, or
repair of piping that has been placed in service. The
provisions of this Code may optionally be applied for
those purposes, although other considerations may also
be necessary.
There are API standards that are used for inspection & testing of tanks and vessels that have been placed in service - I was unsure if there was something similar for piping that had been placed in service.
Regards,
Shane
RE: Pressure Testing of Corroded Piping
In the pipeline code of federal regulations, CFRs Title 49 Parts 192 and 195, repairs to pipelines are addressed and, if the original maximum allowed operating pressure limits are to be maintained, the pipe used in the repair must be tested to the same test pressures used on the original pipe.
RE: Pressure Testing of Corroded Piping
Section 345.2.6 could be used in this respect
"If repairs or additions are made following the leak test, the
affected piping shall be retested, except that for minor
repairs or additions the owner may waive retest requirements
when precautionary measures are taken to assure
sound construction.
There's no limit given of how long after the leak test......
There are standards for assessing fitness for purpose, for pipelines there is B 31G, piping appears to be API 579
Ultimately pressure testing is a simple, established method for providing a level of assurance about a piping system.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Pressure Testing of Corroded Piping
I don't think cutting out and putting in a new section of pipe into your piping system falls under "minor repairs or additions".
I do agree though with your comments that a successful pressure test makes everyone feel warm and fuzzy.
BI,
Agree 100% with your comment
"......although logical is logical and it follows directly" that you should use the same test pressure for the new pipe."
The OP stated the Inspection Engineer queried the testing of old, corroded in service piping at 150% of design pressure.
That is what I have been trying (unsuccessfully) to discuss.
Would it not be more logical to cap the new pipe, pressure test to 150% then install with two golden/closure welds ?
If it is an O&G plant there is a strong possibility the product doesn't like water so to fully remove the product, hydrotest with water, remove the water and reinstate ready to accept product could be quite time consuming.
Mind you, if it is water piping I have just wasted 15 minutes of one finger typing.
Cheers,
Shane
RE: Pressure Testing of Corroded Piping
Test pressures should be specified according to the original requirements, if the pipeline is still to operate at the same pressure. That would be 150% for B31.3, but could be less than 150% for B31.4 or B31.8 designs.
RE: Pressure Testing of Corroded Piping
The OP is just talking originally about pressure testing per se of "old corroded piping". If you're doing an inspection and part of the inspection is to certify that the current piping is good enough for the process conditions, one of the ways to demonstrate that is to do a pressure test. IMO that pressure test should be the same as the original unless the owner has decided to de-rate part of the plant and adjust all the safety devices accordingly ( trips, relief valves etc).
All depends on what you're trying to achieve - close your eyes to the rest of the plant and just test the bit you've had to replace or a full re-test and re-certification of the entire plant.
If you have confidence in the piping then you can do this with process fluid or gas.
A pipeline company I used to work for did a pressure test to design pressure every year in product as a means of demonstrating integrity. Only failed once or twice....
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Pressure Testing of Corroded Piping
My apologies.
I misread the B31.3 clause.
Cheers,
Shane
RE: Pressure Testing of Corroded Piping
Steve Jones
Corrosion Management Consultant
http://www.linkedin.com/pub/8/83b/b04
All answers are personal opinions only and are in no way connected with any employer.
RE: Pressure Testing of Corroded Piping
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.
RE: Pressure Testing of Corroded Piping
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.