ASME B31.3 piping, hydrostatic pressure test, loose blind flanges
ASME B31.3 piping, hydrostatic pressure test, loose blind flanges
(OP)
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
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





RE: ASME B31.3 piping, hydrostatic pressure test, loose blind flanges
Note: I routinely apply the same criteria to flanged valves as well. I either test them as part of the assembled system or I have them tested prior to installation as any test completed by the Manufacturer does not fully satisfy the ASME B31.3 requirements.
Having said this, it is fairly common practice for people to bolt on blind flanges or valves, or install blanks, without properly testing those components.
You may want to review Clause 345.2.3 of B31.3 as this language changed a bit in 2008 to clarify that piping components could be pretested and that if pretested, the flanged joints (when installed into the final system) need not be retested.
RE: ASME B31.3 piping, hydrostatic pressure test, loose blind flanges
Best regards Kristian
RE: ASME B31.3 piping, hydrostatic pressure test, loose blind flanges
thank you
RE: ASME B31.3 piping, hydrostatic pressure test, loose blind flanges
It is a very generic question what I initiated. Basically we talk about all sizes from 1" to 20" and with pressure rating 150# up to 2500#.
Material wise we talk about LTCS (A333, A350LF2, 316L, 22% Cr duplex - and in some few cases 25% Cr super duplex).
The spools are typically operating at design temperatures of max. 50 deg. C, so we are testing them to 1.5 times the design pressure as per the piping specification.
Regards Kristian
RE: ASME B31.3 piping, hydrostatic pressure test, loose blind flanges
RE: ASME B31.3 piping, hydrostatic pressure test, loose blind flanges
RE: ASME B31.3 piping, hydrostatic pressure test, loose blind flanges
For all of the piping I have personally dealt with, I would not accept it. It is not a "proven connection". Until that bolted connection is tested to 1.5x the design pressure, it is not Proven.
RE: ASME B31.3 piping, hydrostatic pressure test, loose blind flanges
RE: ASME B31.3 piping, hydrostatic pressure test, loose blind flanges
RE: ASME B31.3 piping, hydrostatic pressure test, loose blind flanges
I think our problem in relation to this para is that our blind flanges (that was not pressure tested) will be a piping component being connected to the allready tested WN flange on the piping. It is correct, that if the blind flange had been pressure tested separately, we could connect the pipe spool and the blind flange without any problems (without problems in relation to the Inspector).
However, does it make sense at all to make a separate pressure test to 1.5 times design pressure of a loose B16.5 standard flange?
It would be a "strength test", but here we have virgin, forged standard flangesw. I have never heard about such ones fail mechanically during a pressure test. I also have not been able to find any reporting on such ones failing.
RE: ASME B31.3 piping, hydrostatic pressure test, loose blind flanges
Which part of the Code describes those 'new' blind flanges have to be rehydroed? This may well be a case for an interpretation..
Apart from whether or not it's good engineering practice to do a new off-shore hydro, strictly speaking you may argue with the Inspector that B31.3 para 345.1 refers to piping systems; the definition of piping systems in para 300.2 reads
This refers to piping:
So, piping on its term refers to assemblies of piping components.
Flanges, as per the Code definition, are piping components, of course.
Is a blind flange an assembly? No.
Is a blind flange + bolts + gasket + other mating flange (thus a bolted flange joint assembly) an assembly in view of above definiton from B31.3? Probably yes.
I think your case is somewhere in the middle, as part of the assembly has been tested.
Consider the following case. You have 2 pipe spools (A1 & A2), of the same size, design conditions, flange types (say WNRF with SPWND's), same test pressure, etc. To hydrotest them and save time, you make a 'temporary piping system' (say system A) in the shop by hooking up both spools, do the hydro, see how they pass, disassemble them, and install em in the plant. You do the same for spools B1 & B2 (which together make system B), C1 & C2 & C3, D...., etc ..... All these spools in view of this case, have flanged end connections.
Now, all spools are installed at other locations in the plant, compared to how they were hooked up for the hydro; say e.g. A1 is connected to B2, B2 to C3, and C3 to A2, etc. Now, do you have to re-hydro everything all over again, just because the bolted flange joint assemblies during hydro are 'different' compared to the installed condition? I dont think so (but I may be wrong due to my little experience).
This example kind of is the same as what you're dealing with, I think.
Now, I wouldnt agree with the inspector without any discussion or reasoning from his side.
If you have reasons to doubt the integrity of the flanged assembly (i.e. the new blind flange), and are sure the Code requires you to re-do the hydro? Do it.
If you dont have reasons to doubt the joint integrity, and believe the Code doesnt require you to do so, but the inspector does have good reason to re-do the hydro? Do it.
Otherwise, dont get overruled just like that, just because he wants so. Even though he may have some 'rights' based on the Code, doesnt mean he's always right.
Ask him why he thinks it has to be done again.
RE: ASME B31.3 piping, hydrostatic pressure test, loose blind flanges
It is too late now but you will just have to ensure you do not use temporary blinds in place of permanent in future.
If you have an isometric to be fabricated it will show you where permanent blinds are to be installed so you just need to ensure they are installed at the fabrication stage.
Your purchasing department will (or should) look at the material list on the isometric and see eg.2 x W/N Flanges, 2 x elbows, 1 length of pipe, 2 x gaskets, 16 x studs, 32 x nuts and 1 x BLIND FLANGE.
Put it all together with a temporary blind flange on the opposite end to the permanent blind flange and voila! - a code compliant spool piece.
Cheers,
Kiwi
RE: ASME B31.3 piping, hydrostatic pressure test, loose blind flanges
Cheers,
gr2vessels
RE: ASME B31.3 piping, hydrostatic pressure test, loose blind flanges
RE: ASME B31.3 piping, hydrostatic pressure test, loose blind flanges
I will look into this. I understand your point. completely. believe it is not a code requirement but more so a client request. If they are willing to pay, go for it.
RE: ASME B31.3 piping, hydrostatic pressure test, loose blind flanges
RE: ASME B31.3 piping, hydrostatic pressure test, loose blind flanges
While the sensitive leak test of 345.8 is not specifically defined in 345.1, I believe that it may be germane to the case described by Esbjerg provided the Owner accepts.
RE: ASME B31.3 piping, hydrostatic pressure test, loose blind flanges
Your caveats may be excellent reasons for an owner to insist on testing of a scope greater than that of 345.1's required leak test. However, I still don't think that B31.3 requires users to verify by means of hydrotesting or other tests per 345.1, the strength of blind flanges, flanged valves, flanged instruments, pump housings or other such components which have been either previously tested or otherwise certified to standards accepted by B31.3. Do others disagree? I've read the code interpretations as best I could and haven't found anything which would lead me to another conclusion yet.
RE: ASME B31.3 piping, hydrostatic pressure test, loose blind flanges
RE: ASME B31.3 piping, hydrostatic pressure test, loose blind flanges
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
RE: ASME B31.3 piping, hydrostatic pressure test, loose blind flanges
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 ?
RE: ASME B31.3 piping, hydrostatic pressure test, loose blind flanges
The problem was very bad material - but very good certificates (falisfied). The weldability of the material was simply not OK.
RE: ASME B31.3 piping, hydrostatic pressure test, loose blind flanges
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.
RE: ASME B31.3 piping, hydrostatic pressure test, loose blind flanges
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?
RE: ASME B31.3 piping, hydrostatic pressure test, loose blind flanges
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??
RE: ASME B31.3 piping, hydrostatic pressure test, loose blind flanges
What you are doing is standard for ASME VIII new constructed vessels and for repairs to vessels during my 40 years in the industry.
RE: ASME B31.3 piping, hydrostatic pressure test, loose blind flanges
RE: ASME B31.3 piping, hydrostatic pressure test, loose blind flanges
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.
RE: ASME B31.3 piping, hydrostatic pressure test, loose blind flanges
Typo error. Should have been B16.5.
RE: ASME B31.3 piping, hydrostatic pressure test, loose 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.
RE: ASME B31.3 piping, hydrostatic pressure test, loose blind flanges
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
RE: ASME B31.3 piping, hydrostatic pressure test, loose blind flanges
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