PN rating of HDPE pipe and flange adaptor

[nabeel3]

I am working in a project where underground fire water piping is hdpe pipe with a pressure rating of PN20 bars. For valve connection contractor is fusing hdpe stub flange on the hdpe pipe end. pressure rating of stub flange (a.k.a flange adaptor)is PN16. But the thickness of stub end is same as the HDPE pipe. Hence contractor is saying it may a printing mistake by the manufacturer.They say that if the thickness is same as of pipe the pressure rating of stub flange shall also be same. As per project specification stub flange shall be same or greater pressure rating than that of pipe. Is it true that the PN rating depends on the thickness or the SDR of hdpe pipe. Can i accept the contractor work.

 

[mk3223]

IMO, before accepting the material, you may contact the HDPE pipe vendor and confirm if the Contractor statement is actually true or not, and ask for a written statement for the record.
I believe the Manufacturer stamp of PN-16 on the pipe stub end is correct for what it is for. And, I don't think it's an obvious mistake from the manufacturer.

 

[gerhardl]

Hello nabeel3,

I fully agree with mk3223.

I would in addition, as soon as you et the answer from the pipe vendor/manufacturer double check the description for the project. HDPE pipes have indeed a connection between thickness and allowed pressure, but temperature is also, as known,a factor here, even as low as 10, 20 and 30 deg C.

HDPE qulity is a subject for soecialists, and it is important that all parties involved agrees and understand fully construction standards and working conditions, limits and tests.

 

[nabeel3]

Generally speaking, what are the factors on which PN rating of flanges depends upon.?

 

[mk3223]

what are the factors on which PN rating of flanges depends upon.?

Not sure about the question.

But, just guessing to be one of following:
A. because of the operation process
B. because of the pressure test rating for flange
C. because of the pressure rating of the connecting valve

 

[LittleInch]

Nabeel

".They say that if the thickness is same as of pipe the pressure rating of stub flange shall also be same."

It sounds to me like the Contractor is talking utter rubbish.

A stub flange is not rated by the thickness of the pipe stub, it is the strength of the upstand and the strength of the backing ring.

Also I assume it is being connected to a PN 16 rated flange on the PN16 rated valve.

The pressure rating of your system is limited by the lowest rated item. The pressure rating of the pipe is irrelevant so long as it is equal to or higher than the rating of the flange.

PN20 is a little odd as most equipment will be PN 16, PN32, PN 64 etc so it becomes impossible to use the strength in the pipe.

Hence I would fire your contractor for trying to get you to do this.

IMHO


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Also: If you get a response it's polite to respond to it.

 

[nabeel3]

Thank you everybody for taking time to reply my query.
Dear little inch can u tell me what is upstand in this case.

Regards

 

[LittleInch]

I'm sure there's a better name for it but it's the bit the backing flange sits against.

It's the bit the PE100 PN16 is stamped on.

Essentially the backing ring sits against this upstand or stub and hence the shear stress across that piece of PE is what resists the force.

Sometimes there is metal reinforcement, but mostly it's just a thick bit of PE.

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

 

[gerhardl]

A comment on PN20: In the NORSOK standard, developed for offshore North Sea (oil and gas) with the target both of to obtain European standards, including 'sour service', and also to have a renewal with more economical dimensions (slimmer, higher speeds) the PN20 was/is frequently specified and used.

 

[LittleInch]

I'm taking a bit of a stab in the dark here, but it is possible that PN20 is used more to line up with ASME class 150 ( commonly circa 19 bar) maximum rating.

The point remains though - as soon as you stick a PN16 rated fitting onto a PN 20 pipe, it all becomes PN16 rated. Thickness of pipe and the stub flange is irrelevant. For the Contractor to state otherwise is both incorrect and potentially dangerous.

LI

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