ASME B31.3 piping, hydrostatic pressure test, loose blind flanges 7

[Esbjerg]

When we are manufacturing prefab pipe spools for modification projects (offshore oil/gas), these spools are normally pressure tested onshore in the workshop. Often all flanged connections are blinded off using temporary test flanges. And at least one or several of the blinds used during the test is a temporary test flange.

After being installed in the offshore plant, some of the branch connections (or sometimes also end of line) is blinded off using ASME B16.5 standard blind flanges. These are taken directly from stock - and has not been subject to any hydrostatic pressure test.

In the end, after the completion of the new pipe installation, the entire new piping system is subject to a sensitive leak test to 25% of the design pressure.

But we have recently had comments from an Inspector telling us, that the loose blind flanges taken from stock and being installed as part of the piping hook-up should be subject to a pressure test to 1.5 times the design pressure.

As the written text is in B31.3, the Inspector is probably right. I however do not think it is the intentions of B31.3 to hydrostatically test a standard blind flange to 1.5 times the design pressure. The important issue here must be the leak test of the final flange joinings.

I would be happy to receive comments and also to hear about "common practice" in this field.

Thanks in advance

 

[gr2vessels]

I have to confess that I have been in that situation once, few years ago, with similar flanges we purchased for a fraction of the normal price from a dubious supplier. It turned out that we have ignored the forged certifications, for the sake of a saving which proved to be a waste, just like stanweld's experience. I hope he learned what I have learned the hard way.
Buy from reputed supplier, accept only proper certification, so you don't need additional hydrotest for the certified ASME B16.5 / ASME B16.47 flanges.
Just out of curiosity, is there anyone who would hydrotest the spare blank, replacing an old one damaged for any reason?
Cheers,
gr2vessels

 

[MJCronin]

Stanweld,

Who made the defective weld neck flanges ? Were they imported from China ?

What types of pressures/temperatures did they see ?

What types of materials were defective ?

 

[Esbjerg]

@Stanweld + MJCronin. Yes, I have experienced same thing with weld neck flanges (many years ago, 2500# WN flanges from Italy. We also had to change about 250 flanges from that lot.
The problem was very bad material - but very good certificates (falisfied). The weldability of the material was simply not OK.

 

[moltenmetal]

stanweld: it's obviously pretty tough to test a WELD NECK FLANGE without WELDING it first, at which point nobody is going to argue with you that the hydrotest is REQUIRED!

I've never personally seen a weld neck flange fail during a hydro, but I have seen fittings crack during welding and through-wall defects in new welded seam pipe. I've also seen plenty of bad welding, threads cut too deep, inadequate thread engagement during assembly etc. Hydrotests are designed to pick up those defects, or at least the GROSS defects that are apparent before the pipe is put into long-term service, in a way that doesn't hurt anybody.

A blind flange not modified by welding or other means is an entirely different animal than a weld neck flange. So is a flanged valve, a flanged instrument, a pump or a vessel in my opinion. The code either exempts these entirely from its scope (pumps, vessels) or relies on the certification of the manufacturer or the applicable standard (valves, instruments, and flanged piping components). The owner, if they do not feel this is adequately protective for their service conditions and design life, is of course free to perform testing beyond the requirements of the code.

What we're talking about in this thread is the fundamental question of whether the section 345 required leak test in B31.3 is intended to be an assembled system leakage test. Is this test intended to include all components in the piping system, whether or not these have been previously tested or certified and are connected to the piping by a means other than welding? Is it intended to prove the leakage tightness of flanged joints? I'm quite satisfied in my read of 345 and of 326.3 and the rest of B31.3 that this is NOT the intent of the code. The 345 test is not intended to require that the testing be performed on the piping system in the final assembled condition, including all components whether certified or not, or it would have said so in plain language.

 

[stanweld]

MJCronin:
Some of the described defective flanges occured due to the Italian forge shop's purchasing reforging billets that were continuously cast and not subsequently hot rolled. They believed that appropriately hot rolled reforging billets were supplied as purchased. I have seen a number of similar cases from forgings made in China and in the early days from Korea and the US. We have seen actual fracturing of flanges from China - falsified certs. Again the only B31.5 blind flanges that I have seen fail were due to weld repairs - covered up by the manufacturer.

moltenmetal,
We have tested permanently installed blinds in piping systems and left them in. We also do not concern ourselves with leakage at test blinds to block out equipment removed from the test as long as the presure is maintained and joints are visually examined free from for leakage. Removal of items from the test is clearly permited under B31.3. In a number of projects, we have replaced all gaskets and bolting after B31.3 leak testing when required by the contract. We did not replace permanently installed blinds on a number of projects that I have been directly associated.

gr2vessels;
When testing a vessel per ASME Section VIII and there is a flanged flat head (blind) or manway cover (blind) conforming to B31.5, is it customary to replace the head or manway cover with another B31.5 flange from stock?

 

[gr2vessels]

A vesel designed per ASME VIII and uses standard ASME B16.5 flanges, is typically hydrotested with it's final blind flanges. Normally, the blind will not be removed, when the vessel is installed on site. All other nozzles will be covered with blinds typically used for hydrotests and are being re-used perhaps hundreds of time. Some of the larger blind flanges have been custom designed for the hydrotest purpose in order to save a great deal of money.
Also, yes, on the plant is customary to replace an old damaged blind with a new one from stock, certified for the service by a trusted source. I have replaced recently a blind with a threaded hole for a prssure gauge, where the thread corroded in service and could leak. We hydrotested separately the blind because of the threaded joint, not the flange itself. We have never hydrotested a replacement standard blind flange and have never heard of one single failure of a certified blind flange.
Is this all wrong??

 

[stanweld]

gr2vessels,
What you are doing is standard for ASME VIII new constructed vessels and for repairs to vessels during my 40 years in the industry.

 

[XL83NL]

What's a B31.5 flange?

 

[moltenmetal]

gr2vessels: In my experience, what you are doing matches standard industry practice and complies with the applicable codes.

In piping it is customary to replace a corroded or damaged flanged or threaded instrument, valve, blind flange or similar pipe line component not requiring welding, thread-cutting, brazing, swaging etc. as part of the installation, without re-hydrotesting the line to prove the strength of the flanged or threaded joint or of the replacement device. As stanweld points out, B31.3 permits certain devices of this type to be removed prior to the hydrotest, therefore relying on the stamped rating of the device and whatever testing is required for it to meet the standard that applies to that device. Leakage testing of the assembled joints would be done of course before putting a hazardous fluid in the assembled line, but that test would not necessarily be done at the hydrotest pressure. In Category D services, the owner may elect to service test instead.

If threads are cut, welding or brazing or swaging is done etc., a hydrotest after the repair, plus any other NDE required per B31.3, must be performed.

The leakage test in B31.3 345.1 should therefore be understood as a test to prove the joining methods of pipe to fittings etc., not as an assembled piping system leakage test.

I see no CODE reason therefore to require a welded spool to be re-hydrotested after it has passed a hydrotest with a temporary blind flange, merely to prove the strength of the permanent blind flange. Of course you'd use the real flange if you had it, to avoid the need for re-work. The owner can elect to repeat the hydrotest with the real flange if they feel it is prudent, but they cannot claim that it is a requirement of B31.3 to do so in my opinion.

 

[stanweld]

XL83NL,
Typo error. Should have been B16.5.

 

[Leonardobetta]

Back to the initial question; whether testing is required or not. For sure & 100% is certainly required for all flange jts connection (i.e flange-flange, flange to blind flanges).

Note: testing done at Fabshops is to prove the integrety of shop welded jts; whereas, testing done at site is irrelevent testing and for different purpose (i.e flange connection joints or any other new welded jts in case of any modifications).

Furthermore, never forget about safety aspect behind testing requirement which supersede & dominates all other aspects.

 

[joeridebon]

Hello,

We do have a similar problem on a drilling rig.

An existing pipe of 5000 PSI with 5000 PSI working pressure welded in valves.
Some parts of the line and some valves are renewed.

Now is the question do we have to test all to 1.5 X MWP , so 7500 PSI or to 5000 PSI MWP of valves.

Not possible to install blind flanges .

So the old valves will also see 7500 PSI if tested to 1.5 x MWP

Thanks for your reply

 

[Esbjerg]

Hello back,
Your new valves are for sure allready pressure tested by the valve manufacturer.
If the valves are flanged, there is for sure no problem. You may carry out a leak test (sensitive leak test at reduced pressure).

However, if they are welded in, you will have new welds that have not been pressure tested.
If so I would recommend that you pressure test. Would it be possible to set a plug in the pipe?

Otherwise, it might be an option to accept the welds as "golden welds", doing 100% NDT by two different methods. For example X-ray + MPI. ASME B31.3 allows such deviation to the pressure test requirements.

regards
Kristian