Pipe Stress Anaylsis on Thermoplastic (PVDF, PP) - applicable US design codes 2

[S_a_e]

Dear all,

I will soon have to start learning Pipe Stress Analysis in order to be able to perform such calculations for my company. We are water treatment plant producers and we work mainly with thermoplastic materials (PVDF, PP).

The preliminary step for me is to have an overview of which are the applicable design codes that are involved in the calculations (e.g to compute stresses in the pipes, evaluate allowable stresses, ...).

I started by reading ASME B31.3 but in chapter VII it is clearly written that elastic behaviour assumptions (stress proportional to strain) in a wide range of strains is not generally valid. Additionally it seems that this chapter doesn't cover thermoplastic materials with a mathematical approach as extensively as it does for metals.

I have also seen that ASME has released some other design codes ASME NM.1, NM. 3.1, NM. 3.2, NM 3.3 which cover more in detail thermoplastic materials.

My questions are the following:

1) Is ASME B31.3 applicable for the thermoplastic materials I have mentioned?
2) I have found a calculation for PP pipes that was done in Autopipe. The design codes mentioned were ASME B31.3 and ASME B31J for intensification factors. From ASME B31.3 it seemed to use eq. 23a (320.2 Stress Due to Sustained load) which comes from the chapters relevant to metals. Is this approach acceptable given the piping is thermoplastic?
3) Are ASME NM codes "more applicable" than ASME B31.3 for thermoplastics? Or are they complementary to it?

Thank you all for your time

 

[1503-44]

ASME B31.3 may not be applicable. Are you doing some chemical/water processing?
Maybe you should have a look at tha American Water Works Association design and installation methods, standards and specifications for plastic materials.

https://www.awwa.org/portals/0/files/publications/documents/m23lookinside.pdf

https://www.awwa.org/portals/0/files/publications/documents/m55lookinside.pdf

https://www.awwa.org/portals/0/files/publications/documents/m45lookinside.pdf

https://engage.awwa.org/PersonifyEbusiness/Bookstore/Product-Details/productId/81145714

https://engage.awwa.org/PersonifyEbusiness/Bookstore/Product-Details/productId/84701177

https://engage.awwa.org/PersonifyEbusiness/Bookstore/Product-Details/productId/36972557

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[EngrPaper]

B31.3 is notoriously deficient for thermoplastic and thermoset piping. It is one of the main reasons the NM.1-3 codes were developed and are working towards B31.1 and B31.3 integration.

For your thermoplastics, NM.1 will be your go-to. Unfortunately, the piping stress softwares have not kept up with the times and do not use the code equations from NM.1 and NM.2. We have been e-mailing the companies to encourage them to include these new design codes. Until they do, you must get very familiar with the codes and how your stress software calculates stresses and strains (elastic/plastic effects, pressure lengthening, pressure stiffening, etc.) in order to back into a properly stressed pipe.

 

[S_a_e]

Thank you both 1503-44 and EngrPaper.

So I have to assume that a calculation for PP piping (which I have seen issued from a supplier) made on the basis of ASME B31.3 for example calling eq. 23(a) from paragraph 320.2 chapter II (which pertains metal materials), isn't the "proper way", right? ASME NM. xx design codes should have been used.

What would be the equivalent applicable design codes for EU? Am I right to consider DVS 2210-1?

 

[XL83NL]

Sound advice from EngrPaper. Not sure what then EU codes would be but I’ve heard of ISO 14692.

Huub
- You never get what you expect, you only get what you inspect.