CSA Z662 Backfill before testing in Canada requirement

[Dragonvrod]

thread378-250523
I was reading this thread and even though I have respect for everyone on these forums, the assumptions that the CSA Z662 standard not stating explicitly, it does not mean that it is not required. Each province has its own Pipeline regulations are that are mandatory and must be followed. As always the more stringent applies if there is not clarity or a contradiction. So for an example the Alberta Pipeline regulations state in Section 25 of the regulations, Conditions for Pressure Testing, " A licensee shall pressure test a pipeline that will be buried during operation with the full depth of earth cover applied."
You must check each province's regulations as a supplement to the CSA Z662 Standard.

https://www.qp.alberta.ca/1266.cfm?page=2005_091.cfm&leg_type=Regs&isbncln=9780779827220.

As someone who has pipelined for most of my career, it is not a desirable condition to test piping that is not backfilled. It is not safe, and from a project management and schedule perspective a huge disadvantage to the project scope, and the addition of huge costs to leave the ditch open, on any length of pipeline, This would be an entire post just on this topic alone.
The CSA Z662 Standard and the provincial pipeline regulations allow for testing of pre-tested pipe, pipe for road bores and drag sections, to be unexposed, but they will be tested in the final pressure test as well.

 

[1503-44]

Testing a pipeline that will be buried in an unburied state would allow considerably more flexibility thereby resulting in quite different longitudinal stress distributions, however the primary intent is to test hoop stress, which are not much affected by longitudinal restraint. IMO, there is effectively no difference in the test results whether buried or not, although there are, as you say, many very important differences in other factors to consider. Personally I would never consider testing any significant length of cross country pipeline in an unburied state. Short lengths of plant piping is an entirely different matter. If one is faced with such a conflict with regulations, a variance should be obtained to allow testing in the safest manner possible.

 

[GD2]

Dragonvrod,
I agree with your statement that Z662 is not very explicit in the pressure testing procedure and that's how the most Codes are written.
The intent of a hydrostatic test by any Code is to test the structural integrity of the system it is designed to. Pipelines are typically designed for both restrained buried) subject to substantial axial restraint, and unrestrained portion (usually above ground and transition). It is, therefore, imperative that long pipelines should be tested buried.
Even if the Code Z662 is not explicit on this, the Pipeline Act that resulted in AER's AR91/2005, which is supreme is explicit on this.
To the Owner, Designer the apex document is the Act/Regulation and then the Code.

GDD
Canada

 

[LastBornBoy]

If the pipeline were to be tested exposed in the trench (no cover), then it will be a nightmare holding hydrostatic pressure during the hold time of the test because the pipe is exposed to changes in temperature. As the temperature changes, the pressure in the pipeline responds and changes accordingly. For an 8-hour test, that temperature variation could be in the magnitude of 20C delta.
I have seen a few designs by EPC companies with test sections maxed out to 109.7% leaving not much room between meeting minimum pressure and exceeding maximum allowed pressure equivalent of 110% SMYS. I reject these kinds of test sectioning all the time. Field elevation changes, a slight change in test stations and yes temperature variation can swing a test like that beyond the maximum of 110% SMYS easily if tested exposed for 8 hours.

It is never a good idea to not bury the pipeline for final mainline pressure testing. It is never a good idea to not backfill immediately as soon as you can. There are tons of things that could go wrong from erosion control to wildlife trap, to frozen backfill, right of way utilization constraint because of un-backfilled spoil piles everywhere etc. I can not think of a single benefit to leaving the trench open until after the pressure test.