Hydro-test methodology for Above ground laid 18" NB natural gas pipe line.

[pdprao]

What is the hydro-test methodology for Natural gas pipe line with test pressure of 74 bar which is laid above ground of 800 m length . The line is designed as per ASME 31.8 and being tested separately.
a) Whether Underground pipe line hydro test procedures as per API- 1110 which is based on hydro-test pressure drop acceptance value criteria with PV plots & air volume calculation is it really applicable for this Pipe line which is laid above ground and where all the weld joints/ components are readily accessible for visual inspection.??
b) what is applicable code clause for Hydro-test criteria of the High pressure gas pipe line laid above ground and relevant acceptance standards of hydro-test results. ASME 31.8 does not give clearly the requirements for above ground Gas pipe line hydro test requirements.
Techman

 

[BigInch]

It seems that you don't know why you are using API-1110.

Should be applicable to both above or below ground, although above ground may be more challenging to conduct the test successfully and quickly. You must get the air out, so API 1110 is even more applicable to above ground testing, where that will be even more sensitive air expansion pressures.

B31.8 does give test requirement: The pipe must hold minimum test pressure for the duration of the testing time.

you must get smarter than the software you're using.

 

[pdprao]

Thanks for your reply Mr BigInch. If the weld joints and full Pipe line is 100% accessible for visual examination during hydro test, why one need to adopt indirect method of water-loss assessment( by Pressure drop) with various corrections as applicable for underground pipe line? . If we are having proper vent points and water filling is done with batching pigs for effective filling , can we follow station piping hydro-test requirements.

 

[LittleInch]

As with a similar post, the real problem is that B 31.8 clearly doesn't do wholly above ground piping very well, which is to be expected as this is a pipeline code which is usually buried.

You have two options:

Do the test as best you can to B 31.8 (at night might be your best option) and get some big volume / pressure swings due to thermal expansion / contraction.

Write to the client stating that in this instance (wholly above ground, all joints visible) testing to the code will be difficult and visual inspection of all welds will be undertaken to reduce the testing time, but the minimum test pressure maintained. However acceptance would be by visual inspection, not by PV pressure/temperature compensation.

You really need to make sure though that the pipe is completely filled with water.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Duwe6]

"However acceptance would be by visual inspection, not by PV pressure/temperature compensation."

What he said.
Tell the client that you will be upgrading to a more sensitive test that uses ASME methodology for exposed piping. Sounds good, is factual, and the test is simple and fast. Full hydro pressure for 10-minutes, reduce the pressure to between design and hydro, and walk the line, examining all joints. Actually more sensitive than a B31.8 buried-pipe hydro. This meets Sect VIII, B31.1, B31.3 and other Codes.

 

[pdprao]

The Pipe line is laid above ground and having 5 Nos of vertical thermal expansion loops.Client has accepted for the proposal in principle to carryout hydro-test on the line with visual examination for leakages of welds /pipe line in-lieu of underground hydro-test procedure . As discussed in the forum ,due to anticipated problems of pressure swings due to temperature changes and problem of ineffective venting the underground procedure is not preferred.

Now the issue is as to how to meet Code compliance and regulatory compliance . I need to propose the actual test methodology with test parameters and acceptance criteria . Perhaps the procedure is going to be a hybrid procedure with mix of requirements of API-1110 , B 31.8 and B31.4/B31.3/B31.1.

The following steps may form as part of procedure.

1) 1.4 X Design Pressure(DP) will be the Hydro test pressure ( location class 4 ) as per B31.8.
2) Filling & draining procedures and Pressurization & depressurization steps will be as per B 31.8 and API-1110 including pressure cycling. Air content test shall be performed to establish the effective venting of the system. Vent valves provided on loops will be utilized to improve the venting.
3) Spike test will be done for 1 Hr at 1.5x DP .( Design is verified to be very safe for 1.5 x DP) for 1 hr
4)Strength test will be performed at 1.4x DP and test pressure maintained for 4 hrs. At the same time visual examination shall be carried of all pipe line welds and pressure boundary. ( B31.4 ). It may be preferable to do the visual examination at DP as per B31.1 in view of safety.

I agree with Little Inch that B 31.8 is silent about A/G portion of Pipe line ,if it is to be hydro-tested.
Looking for valuable comments from Hydro-test/ design experts of Gas Pipe Lines .

 

[BigInch]

Duwe6, That doesn't meet the B31.8 code's holdtime requirement.

pdprao,
B31.8 is not silent on above ground testing.
B31.8 is the applicable code for every and all things pipeline.
B31.8 does not care if pipe is above or below ground, onshore or offshore.

Pipeline Testing
Visual inspection of pipeline joints are completed before burial and testing is conducted after burial.
No visual inspection is required during the test.
Visual inspection is not to see leaks, only to verify joint integrity, nothing visibly wrong: finished.
Visual inspection means nothing in regard to verification of strength.

What's your design class location factor, wall thickness and minimum yield strength?

you must get smarter than the software you're using.

 

[pdprao]

To clarify to Mr Biginch

1 B31.8 does not exclude a/g pipe lines . Agreed. But it also does not treat the A/g pipe line subject . Basically it appears , its focus is on underground pipe lines.
2 Visual Examination: Visual examination as per ASME pressure vessels code and other codes like B31.1,B31.3,B31.4 and Nuclear codes NB, NC, ND calls for examination of weld joints , pressure boundary for any leakages and excessive deformation of pressure boundary during hydro-test at a specified pressure . B 31.1 does not refer to this aspect of visual examination during hydro test since its focus is on underground pipe lines where the joints are not visible or accessible for examination. B31.4 in contrast which is applicable to hydrocarbon liquids considers the visual examination aspects . In-fact B 31.8 which is applicable to gas pipe lines with high degree of stored energy in service should not ignore the visual examination on a/g pipe lines from safety point of view. I agree with Mr Dewe6 that B31.8 tests are less sensitive compared to other codes of ASME for comparable design services.
3. The design details of pipe line under consideration is as given bellow.
Design class : 300 #
location class 4: Design Factor 0.4
wall thickness : 8.7mm
Pipe : API 5L 18"NB Grade x 65.

 

[pdprao]

Mr Big Inch:

In line no 3 of above thread , please note to read as " B31.8" in place of "B31.1" which is a typographical error .

 

[BigInch]

1.) B31.8 addresses restrained and unrestrained pipe. Restrained is typically below ground. Unrestrained is typically above ground, although you can make either act in either manner as you like.
2.) B31.4 and 8 visual examination of joints is not ignored. It is conducted before lowering and burial, therefore it is not necessary to examine them again. Although you may want to leave underground flanges exposed during leak testing, generally the pipeline will be otherwise totally buried, but no matter if it is above ground.

"B31.4 in contrast which is applicable to hydrocarbon liquids considers the visual examination aspects . In-fact B 31.8 which is applicable to gas pipe lines with high degree of stored energy in service should not ignore the visual examination on a/g pipe lines from safety point of view."
Nice thought, but not exactly. In fact being able to see a leak at a high pressure energy level means that you have not properly evacuated the area before testing began.

Being able to see a leak during testing would only apply if conducting a leak test, which is conducted at a very much lower pressure (not in the high energy level you refer).

So you use the same B31.8 hydrotest procedure for above or below ground pipe.
Your pipe can be tested up to 170 barg (at normal temperatures).

you must get smarter than the software you're using.

 

[Duwe6]

Apples, Oranges

B31.1 and B31.3 are written around above-ground piping and do u/g pipe badly.
B31.8 is written around u/g piping and does in-the-rack piping badly.

You can order a steak at the chinese restaurant, or order spaghetti at a steakhouse. I recommend that if you want chinese you go to a chinese joint. And that you use 'Rack Pipe' procedures and criteria to hydro rack pipe. Yes, the u/g criteria will work, but the problems have already peeked out.

"Nice thought, but not exactly. In fact being able to see a leak at a high pressure energy level means that you have not properly evacuated the area before testing began." With rack pipe and a good hydro crew, all the air got vented out of the line and standing close to the pipe is actually safe [but I only do it if I personally witness all the vents being 'burped']. U/G pipe generally does not have that luxury, so it is damn dangerous at hydro pressure, to to trapped air. Apples, Oranges.

 

[pdprao]

Observations of MrDewe6 are very relevant about code inadequacy .
Mr Biginch remarks on" Visual examination" needs some comments. Various ASME Codes of Pr vessels and Piping calls for Visual examination of Weld joints and pressure boundary at Design Pressure for absence of any evidence of sweating/weeping during hydro-test for acceptance of Hydro-test results . In contrast Mr Biginch comments of visual examination on Underground pipe welds is pertaining to in-process visual inspection such weld profile , appearance , NDT etc before the joints are coated and the line is back-filled well before hydro-test stage .
Also the issue is not about improper venting and resulting leakage and safety issues during Hydro-test. Such methods of examination is well established procedures in Steam pipe line and other high pressure pipe line construction codes of practice.
The issue is about Ruling-out any evidence of Wetting /weeping on weld surface and HAZ of Joints, during Hydro-test , during 4 Hrs pressure holding period as per B 31.4 when applied for A/g portion of Gas pipe line in lieu-of B31.8 requirements.
Yes ,it is a deviation from B31.8 requirements.The proposal is Only to improve the integrity and review of its technical merits.

 

[BigInch]

Pipelines are nearly 100% buried making your proposal extremely impractical to apply to B31.4 or 8, however you are free to apply that technique anywhere you like, if in your judgement it is necessary.

you must get smarter than the software you're using.