Initial Test Service in lieu of Hydrostatic Test ASME B31.1 1

[anapaz79]

Hi all,

I am currently working on a Thermosolar Plant where a molten salts are the fluid to be heated in order to obtain steam afterwards. This molten salt line goes up through a tower of 250 m, and as the salts solidify at high temperatures, to avoid damage on the flanges face it was decided not to use flanges. This is, the line goes up in zig-zag from the ground level, up to 250 m completely butt welded. The material of the pipe is A312 TP347H, that in order to save material costs was stratified in different schedules, since pressure shall be quite different at the bottom where the molten salts pump is located, than at the top where pressure reduces 85% aprox.

Now, my question is if we can proceed with an Initial Test Service, in lieu of an standard hydrostatic test. As per ASME B31.1 para. 137.7 (code that applies), I kind of understand that I could use this alternative, since I do not have valves or blinds to isolate the line, and obviously temporary closures are unpractical (all site works are quite complicated due to the nature of the layout of the line). Does any one have any experience on this matter? Since I really do not find any limitation in ASME B31.1 to use this testing method, other than it can't be used for Boiler External Piping (not the case).

Design conditions of the line are 40 bar of design pressure at the bottom (pump) and 593ºC.

Any repply or personal experience on this field shall be fully appreciated.

Regards!

 

[themad1]

Hi.

I personally had experience in many commissioning of natual gar tratment plant for power stations.

Before to test hydrostatically the piping welded on field we usually made a low pressure test using air at maximum 6 bar increasing pessure in step of 2 bar with a leak check on weldings on the whole line at each step.

Safe, simple and effective

 

[XL83NL]

No experience here but have you considered 137.7.1, first sentence; "When specified by the owner, ..."

 

[anapaz79]

Thanks themad,

have you ever waived the hydrotest by using the low pressure test. Safety is my main concern in this case.

Regards!

 

[themad1]

Never happened.

Pneumatic test can be used as alternative of hydro test only if done as required by ASME B31.1 par. 137.5
But Pneumatic tests are potentially more dangerous than hydrostatic so you must to go through a adequate risk assessment.

Low pressure test is done as a means of locating major leaks and save time during hydro test.
But I never had problems with hydro test with a low pressure air test done before.

 

[anapaz79]

Hi XL83NL!

This is a very particular project, we engineering, contrustor and owner are the same company, so that should not be a big deal. I am just wondering if this is a good engineering practice!

Regards!

 

[XL83NL]

If hydro-ing is really impractical, go for the pneumatic test as themad1 mentioned. To assess the risks involved, review ASME PCC-2 part 5, article 5.1.

 

[mbt22]

have you ever waived the hydrotest by using the low pressure test. Safety is my main concern in this case.

No, a low pressure pneumatic tests are not a substiture for high pressure hydro or pneumatic tests. High pressure tests are 'proof' tests for weld integrity, low pressure tests find leaks.

Where in the world are you? Is there an insurance company involved? Some form of pressure equipment regulations?

Matt

*Editted to correctly attribute quotation, my apologies.

 

[XL83NL]

He thats not my quote!

 

[anapaz79]

Hi Matt,

I don´t thick that you read my first post, I am basing my question on ASME B31.1 para 137.3.2 which states:

"Nonbolier external piping. As an alternative NBEP, when specified by the owner, the piping may be leak tested in accordance with para. 137.7"

Para. 137.7 states:

"When specified by the owner, an initial service test and examination is acceptable when other types of test are not practical or when leak thightness is demonstrable due to the nature of the service. One example is piping where shutt-off valves are not avaliable for isotaling a line and where temporary closures are impractical. An initial service test is not applicable to boiler external piping"

In no case am I trying to swich hydrostatic test for pneumatic, that´s out of the question, or waiving the riquirement, but more using the alternative ASME seems to allow when no isolation of the line is possible.

So to answer your question Where in the world are you? I am basically in ASME B31.1 world.

As I explained I would like to have some personal expertise with Initial Service Test, not to generate a debate Hysdrostatic vs. Pneumatic.

Thanks a lot

 

[bimr]

First off, as XL83NL posted, you have the problem with: "When specified by the owner, ..."

Secondly, "an initial service test and examination is acceptable when other types of tests are not practical". Just because it is inconvenient, does not mean that it not practical.

Third, the test fluid is the service fluid. This test is only applicable to piping in Category D fluid service. Is it feasible to test with molten salt?

http://www.psig.sg/Don/B31.3 Process Piping Course - 13 Inspection, Examination and Testing.pdf

 

[anapaz79]

Hi birm,

As I stated above, this is a particular project where engineering, constructor and owner belong to the same company, so abut the owner statement that should nor be a problem.

Second: an initial service test and examination is acceptable when other types of tests are not practical". Just because it is inconvenient, does not mean that it not practical. I don´t think it is only an inconvinient, if you read my first post you may understand why it is much more than an inconvinient.


Third: Third, the test fluid is the service fluid. This test is only applicable to piping in Category D fluid service. Is it feasible to test with molten salt? This applies to ASME B31.3, but not to ASME B31.1 which is the ASME that rules this project. ASME B31.1 does not mention anything about fluid to perform the Initial Service Test. Obviously this is one of my concerns, since it does not state anything, and of couirse if it had to be molten salts to be used, that would complicate the situation since they solidify at arround 200ºC.

Again, I just wanted to know anyone´s experience on this, ASME B31.1 differs quite a lot from ASME B31.1.

In any case it is always a good debate.

Thanks

 

[anapaz79]

Correction

ASME B31.1 differs quite a lot from ASME B31.3.

 

[mbt22]

anapaz79,

The reason for the location question was the California circular giving an alternative to B31.1 that might provide you with other options.

The only service tests I've done haven't been B31.1, but focused on the consequences of failure - some calcs to assess what the worst that could happen in the event of a failure and how do I make sure that no-one gets hurt if it does happen. I guess in your case, what happens to the inventory of hot salt (sodium and potassium nitrates?) on release, how far can it spray and what are the environment consequences.

How far through the project are you? Is it too late to incorporate an end cap that gets field cut off for a golden weld tie in? If you're into reducing the risk of service testing, specify additional NDT - maybe looking at what pipelines do for their golden welds?

Matt

 

[bimr]

One would think the term "Initial Service" is self explanatory.

B31.1 Initial Service Test General Procedures

1. This test applies only when specified by the Owner when other types of test are not practical.
2. The test fluid is the service fluid.
3. With the system connected to its permanent supply gradually fill the system with service fluid. If it is liquid, vent the system as it fills.
4. Once the system is filled and vented (if required), continue to pressurize in stages, allowing piping strains to equalize, until the operating pressure is reached.
5. During fill and pressurization, continually walk system down checking for leaks.
6. Once filled and brought to operating pressure hold for a minimum of 10 minutes or until all joints are examined.

http://www.wmhuittco.com/images/Leak_Testing.pdf

 

[KevinNZ]

We more often than not only have service tests for our geothermal steam and water lines. When designed with corrosion allowance there very little chance of the new line failing under pressure. The service test is looking for leaks and not putting high stress on the welds.