HDPE pipeline crossing

[gwkwong]

My Client wants me to check if the HDPE pipeline is ok under the earth and vehicle load. Could someone kindly point me to the article, specfications, formulas that I can base my calcualtion on?

Thnaks

 

[gwkwong]

forgot to mention that it is under 120 psi pressure

 

[TenPenny]

I think page 7 or 8 of this will help

http://www.kwhpipe.ca/Link.aspx?id=1097884

 

[rneill]

I normally err on the safe side and require casing for HDPE under roadways.

Manufacturer should provide data on allowable loads and then you would need to use an appropriate procedure to determine the imposed loads.

Try Section 3 of the Report "Development of a Pipeline Surface Loading Screening Process & ASsessment of Surface Load Dispensing Methods" CEPA Report 05-44. Available online if you search for it.

 

[gwkwong]

Thanks so much for all the help. I wonder if anyone is familiar with CSA Z662. In pressure checking, should the hoop stress be compared to the yield strength of the material or the factored yield strength (design factor, location factor , temperature factor.....)

 

[SNORGY]

Compare hoop stress to SMYS x FxLxJxT for pressure design.
Compare hoop stress to PTSV for notch toughness requirements.

Regards,

SNORGY.

 

[SNORGY]

Sorry...I forgot to clue in to the fact that you may be asking specifically about HDPE - my post was assuming steel pipe. I think you want to refer to Clause 13, since the rules are different and relate to the manufacturer's pressure rating of the non-metallic pipe.

Regards,

SNORGY.

 

[gwkwong]

Yes I switch my topic because I was dealing with steel pipe as well. I agree that the hoop stress to be calculated based on the design pressure and then check with the SMYSxFxTxLxJ. But my project manager who has been in the pipeline told me that CSA allow the hoop stress compare to yield, which I cannot find any reference from the guideline.

 

[SNORGY]

If by "pressure checking" you mean "during pressure testing", then yes, your project manager is correct in that you can pressure test with hoop stresses up to the yield stress.

In some instances you can test in excess of yield stress, like in class locations 1 and 2 with a liquid test medium, provided you don't exceed 0.2% deviation on a P-V plot.

Regards,

SNORGY.

 

[gwkwong]

Snorgy, I spent lots of time researching and find out yes they could pressure test up to or may even exceed 100%. But in Alberta Pipeline Act (

http://www.qp.alberta.ca/574.cfm?page=2005_091.cfm&leg_type=Regs&isbncln=9780779743919),

section 2 part 16 - I think they limited the design stress level to 0.6 SMYS.

Up to now, the way I understand is when designing the MAOP based on the SMYS and other factors (F,J,T...), we would need to check against 0.6 SMYS. That is to say, if the pipeline is design for open field and no traffic then F = 0.8 and the other factors are 1. Say if one day someone whats to cross the pipeline, then the location factor may become 0.75. In this case, the MAOP has to adjust in order to make sure that it is ok for 0.6 SMYS. Correct me if my understanding is wrong.

 

[stanier]

Suggest you download Australian Stnadard AS 2566 from SAIGlobal. There may be an AWWA equivalent.

Books worth reading:-

Buried Piping Design by Moser

Structural Mechanics of Buried Pipelines by Watkins et al

 

[SNORGY]

gwkwong:

The section in the Alberta Regulation to which you refer relates to buried sour gas pipelines, and it is the maximum Design Operating Stress (DOS) level permitted relative to SMYS. However, you *can* hydrostatically test to higher than this level, and indeed as high as 110% SMYS (subject to previously mentioned limitations), if you want. The catch would be that if you want to exceed 100% of SMYS during a hydrostatic test, the ERCB would require a non-routine pipeline license application (as well as the P-V plot referenced in 36 of the Regulation).

The "design factor" to apply in establishing your pressure design thickness boils down to the minimum of FxLxJxT (From CSA Z662-07 Class Locations and the Tables in Clause 4) or that read from the applicable Regulation.

In other words...

DF = MIN [FxLxJxT, F(Regulation)]

Regards,

SNORGY.

 

[SNORGY]

Make that P-V plot "per 32 of the Regulation".

Regards,

SNORGY.

 

[rneill]

Concur with Snorgy, the Alberta Regulation is specific to buried sour pipelines (the equivalent restriction above ground is 0.5). You would do your design to CSA and then if the overall result of FxLxJxT was greater than 0.6 you would use 0.6 - if it was less than 0.6, you would use the calculated value.

You can still hydrotest to a value higher than 100% of yield but it would not be required in this case since the Alberta Regulation requires a hydrotest of only 1.4X the MOP for sour pipelines. Since the MOP can be no more than 0.6x.SMYS then 1.4X the MOP can be no more than 0.84xSMYS. You can certainly test higher if you like, but there is no Regulatory requirement to do so.

 

[gwkwong]

I got it. Very useful and clear thanks to all.