Pressure Testing after backfilling

[Hussain Al Binali]

Greetings All,

I read in a previous thread that CSA Z662 requires pressure testing after backfilling. However, I read this standard but I didn’t find this requirement. Can someone please point me out to this requirement in this code? Which clause? Also, are there other standards that mandate the same thing. In my company we apply pressure testing while joints are exposed for underground nonmetallic piping. I want to share this practice here but I desperately needs the exact quotation.

Thanks

 

[LittleInch]

Not sure about CSA, but e.g. B31.4 states that tests shall be made upon "the completed system". section 437.1

That leaves a lot of interpretation.

I've always argued, usually successfully, that this means that you test the fully installed and completed backfilled system, so you might not have undertaken final reinstatement but back filling imposes or relieves stresses during a test and to do it without backfilling is not the correct way or a test of the "fully installed system".

Now I know codes like B31.3 require all the joints / welds to be exposed which is one reason why it is such a poor code for buried pipe.

For me I would backfill it all and test as a single completed item.

But I think you might struggle to find the precise wording you're looking for. Design codes try not to that prescriptive and leave circumstances to each individual and "engineering judgement".



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

I am not familiar with CSA Z662, however most pipeline codes do not require burial at all, at least in most circumstances, so I doubt that there actually is any requirement for the pipeline to be buried before hydrotesting. I am glad to hear that you read the standard yourself and I suspect that you are correct. So, the only place I know of that actually requires burial is in USA ofshore waters where water depth is less than 200 ft. and for underground road and river crossings, otherwise pipeline burial is optional. Pipelines are normally underground for a number of reasons, and are normally hydrotested without having joints exposed, but many pipelines are not buried; simply laid on the land's surface or on the ocean floor, provided of course that there are no resultant stability issues.

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

 

[Hussain Al Binali]

Thanks a lot for providing your expertises. This is my first post and I am glad that people are active here and helpful. I hope to hear more responses.

 

[1503-44]

Supposedly CSA has a free view/access plan for that standard, but the link and searches related to such link, also shown on the CSA own site, don't seem to work.

https://napipelines.com/neb-makes-important-pipeline-safety-standard-publicly-available/

I have joined the community there and submitted a query to CSA about it.




“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

 

[1503-44]

CSA has explained that I found an old link and the free view program has expired. I asked them if Z663 requires burial before hydrotesting. Wonder if they will answer.

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

 

[Hussain Al Binali]

Thanks ax1e

 

[FacEngrPE]

You might try viewing the standard per this

https://www.cer-rec.gc.ca/sftnvrnmnt/xtntc-eng.html

the link is supposed to be current. Personally I would want to hydro-static test for leaks before burring the pipe. But take some care with your test design as proof testing makes a pipe lengthen and straighten. It is important to bury enough of the pipeline that it will be dimensionally stable during the test. Sometime it is necessary to test once to prove no leaks (joints exposed, lower pressure) and once to meet code proof test requirements.

It is important to note that if you were to do the pipe calculations unburied, and buried the results can be substantially different. See this for an explaination

https://whatispiping.com/underground-piping.

For non metallic pipe proof testing with ends restrained, and unburied along it's length, there is significant risk of the pipe snaking. For non metallic pipe I have found information posted as PPI useful, not sure if it is relevant to the CSA world

https://www.performancepipe.com/

Fred

 

[LittleInch]

This issue of testing before or after backfill and leaving joints open for inspection for leaks is a key difference between piping and pipelines, both in code test requirements and inspection.

Piping, being predominantly above ground likes to do this leak testing of joints and extends it to buried piping.

Pipelines on the other hand recognise that leaving open hundreds or thousands of welded joints on a pipeline pressure test is both impractical and dangerous in the long term because those joints will need to be exposed to allow it be checked and hence need to be joint coated below ground leading to many more corrosion defects than doing it on the surface.

Also, end cap effects (making the pipeline lengthen) only apply close to the end points. For a fully restrained pipeline, the poissons effect tries to shorten the pipeline and results in tensile forces if there is no temperature difference.

I'm not sure if you're trying to show that joints should be exposed during hydrotest ( bad decision IMHO) or not.

ax1e - I can only assume you're referring to offshore pipelines when I agree with you.

Yes there are surface laid pipelines, but this is not normally a great idea other than desert oilfield type lines. Design codes allow for buried fully restrained lines or surface laid unrestrained lines.

The issue here is the pipe is going to be buried - when do you backfill, before or after hydrotest or some halfway house. MY view has always been that a pipeline hydrotest is a strength test designed to test the "as installed" condition. That means fully buried if the pipe is designed to be buried.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

On or offshore. Of course most pipelines are buried for many obvious and some not-so obvious reasons, however burial is not actually required outside of the areas specifically designated by the code, provided the pipeline can be "protected by other means". The Alaska Pipeline has many unburied sections and is supported on specially insulated H-Posts to prevent melting of permafrost that would have occured if the pipeline had been installed in the ground. Additionally it has a number of elevated sections that allow crossing by caribou herds.



“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

 

[LittleInch]

I'll give you that, however then the design would be above ground and it's all ok. The question here is that the design of the pipeline is a buried pipe, but for reasons unknown, the OP doesn't want to backfill the line before he or she hydrotests it. Does the code require backfill on the basis that that is the final installed condition or not.

Different issue than whether all pipelines should be buried.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

Well as I've said, I don't know what CSA Z662 requires. I have my suspisions that they do not require backfill before testing, nor do they require exposed joints, as it is a pipeline code, however since I do not have a copy of that standard, I have asked them for confirmation. I also don't think their website manager is not exactly the right guy to ask, but ... we'll see if I get any response from them. The ASME B31.4, 8 and the CFRs don't state any requirements, either way and I don't recall any other international pipeline codes that I have read from time to time ever mentioning that burial was required before hydrotesting... or not. As you say, as hydrotesting is just about the last thing that you do in pipeline construction, it isn't very smart, or convenient, to leave hundreds of joints uncovered for long periods of time. Most construction contracts, as I'm sure you know, call for limiting exposed pipeline segments to time periods of no greater than 2wks to around 30 days maximum and/or to lengths not exceeding 25mi. Besides that, again as I'm sure you know, it is far more difficult to get temperature and pressure stabilization on exposed pipelines before and during the hydrotest and I am also a believer in your testing in the installed condition, least anybody claim that otherwise would amount to prefabricated assemblies (constructed in place), requiring pre-testing to higher pressures.

So, until I have an opportunity to read Z662 myself, I will put my faith in Hussain's reading and analysis, as that is consistent with everything I know about testing pipelines until now.

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

 

[LittleInch]

I should have looked in my technical library, but I have a copy of the 2015 code.

The relevant (rather vague) wording is similar to the ASME codes, i.e.
"8.1.2
Except as allowed by Clause 8.1.3, 8.1.7 or 8.4, piping shall be pressure tested in place after installation
but before being put into operation."

So it depends on your definition of "after installation". My view I think now is quite clear, but as there will be many versions of "installation" then I don't find it difficult to believe that the code doesn't mandate it (backfilling).

What they say later on is that if the joints are exposed you don't need to do the subsequent leak test, but that's about it.

I did a search on back fill and nothing relevant to this came up.

The commentary on this section is equally vague
"8.1.2
This is a commentary on Clause 8.1.2.
Pressure testing of piping prior to operation is intended to confirm the structural integrity of the piping,
and it is used as the basis for establishing its maximum operating pressure."

I don't know how you can say 100% that the test confirms the structural integrity if you have't back filled the thing when the design calls for it. In these circumstance always think of trying to answer that question posed by some smart lawyer claiming compensation from you or your company because you didn't follow the procedures. Those guys work in digital answers, not the analogue ones we all work in as engineers.



"

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

Great. IMO, burial in the sense of maintaining structural integrity and pressure containment isn't going to make any real difference in most cases, as a pipeline that depended directly on burial so as to not explode, would be a poor design to say the least. But there may be cases where burial is essential to maintaining integrity and pressure strength under solely operational loads, such as when upheavel conditions prevail and the absence of soil weight above the pipe could allow it to buckle upwards and possibly lose pressure containment. In that situation I can see definite advantages to burial before testing, but as we know, that is the usual method of pipeline testing anyway. As for having joints exposed during testing of pipelines, that simply is not often going to be practical. If it is truely practical, than OK, why not. One can use the vagueness of the code requirements to take advantage of either situation as long as you can rule out that there are no specific reasons that would tend to dramatically favor one over the other.

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"