BS 6364: "initial system proving" for Cryo-Testing 2

[NGiLuzzu]

In BS 6364 standard (Issue 3, September 1998), clause A.3.1.2 it is stated: "Make an initial proving test at the maximum seat test pressure (...) at ambient temperature using helium gas to ensure that the valve is in a suitable condition for the test to proceed". This shall repeated at cryogenic temperature [clause A.3.1.4(b)].
How do you understand this? What is the "suitable condition (...) to proceed"? Does it refer to the valve seat leakage, to the shell tightness or both? And what about external tightness of the "system" (test tubing, connections, pressure gauges, etc.)?
Knowing the actual meaning of this requirement is quite important, as it is present in many Cuystomers' and Project Specifications about Cryogenic Tests of Valves (such as Bechtel Engineering documents...).

Thanks to all, 'NGL

 

[scalleke]

Hello Anegri,

We have been at odds with Bechtel about the exact same statement.

Bechtel has argued that the initial proving test is a seat test and not a shell test.

We had argued that it was a system test to prove the valve and the additional piping that is connected to the valve, prior to actually submerging in cold Nitrogen.

No such Luck.

Bechtel insisted that it is a high pressure seat test and thus we have changed our test procedure to reflect that.

We have even gone to BS to get clarification and we have not gotten any.

Best regards.

Scalleke

 

[NGiLuzzu]

Scalleke,
many thanks for your valued advice, as usual!
Reading BS 6364 again, we noticed that in the above mentioned paragraph, reference is made to clause A.3.4(d) which deals with test pressure values and increments. Two things can be noticed:
1) reference to a subsequent paragraph, instead of a previous one, is quite unusual and not linear by the logical point of view;
2) if you admit there can be a typing error, the reference may be also to clause A.3.2.4(d) as well. This means insulating the system from the flowmeter, pressurizing up to maximum test value for 15 min and no visible leakage (whatever the hell this means...!) from valve gland and body/bonnet joint.

This makes much more sense than a seat leakage test at maximum pressure before the "actual" cryogenic test with pressure steps.
We are therefore going to submit to Bechtel a test procedure revised as per the interpretation of above point 2): I'll let you know the comments that will come back.

I also was wondering about asking the question to BSI, too... how long ago did you send your inquiry?

Best regards, 'NGL

 

[gjchk]

It is interesting to read both of your comments about this issue and most interesting to read your comments on how Bechtel has responded to this issue. I work for Bechtel Houston and I am the person mostly responsible for cryogenic testing of valves issues. I have not been approached by anyone requesting my opinion on this matter so I am surprised as you sound to be at the answers you have received. As I indicated in a previous reply, the system proving test is to "prove" the system before cooling starts. Ths system is clearly defined in BS6364. Shell and Seat tests are usually independently done prior to any cryogenic testing as per requirements of API598 but these are mainly to determine valve integrity.

 

[NGiLuzzu]

Gjchk,
maybe you'll find interesting to know that the mentioned test is on valves for Darwin LNG project (plant located at Wickham Point, Northern Territory, Australia) and the Bechtel's reference document no. is 3PS-PV00-F001 (Rev. 00B of January 8th, 2003).
We have already submitted several cryogenic testing procedures according to the same or similar documents, but for different projects (e.g.: Egyptian LNG for Behera NGL Co. in Idku, Egypt...), without receiving any comments about "initial system proving" test or test sequence.

Many Thanks, 'NGL


* PS (to all): for the same issue, take a look to Thread774-81125 in the "Cryogenic Engineering" Forum, too.

 

[scalleke]

Well, this sure is news!

I have reviewed our correspondence with Bechtel stand by my previous post.

Possibly we can take this back up with Bechtel Houston.

Best Regards.

Scalleke