Plastic pipe on Pipe racks

[KatB0605]

Hi everyone!

I know that placing plastic pipe in pipe racks is a NO NO, but I would like to know more about the reasoning behind this.
Other than plastic pipe not having the the same span loads as metal pipe and therefore requires a greater number of support points and temperature limitations, what else is there?

Thanks!

Kat

 

[MJCronin]

Plastic pipe offers zero fire protection and,...

Unless supported every 3-4 feet will begin to slowly sag (creep)under common refinery conditions

As I recall, both B31.1 and B31.3 prohibit using plastic pipe to convey flammable liquids

Repost this in the Pipelines. "Piping and Fluid Mechanics engineering" forum

MJCronin
Sr. Process Engineer

 

[EdStainless]

I have seen plastic cooling water lines in racks, with continuous support under them. They used a steel channel to prevent sagging and it was non-critical service.

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P.E. Metallurgy

 

[TugboatEng]

PVC and especially CPVC are quite flame resistant. They are, however, non-conductive and that can cause static electricity problems when handling non-conductive fluids. I have seen the discharge in person on a small hand truck mounted filter cart that was using a plastic pipe to reach into the sump of a turbogenerator. The arc lit up the entire arm of the unfortunate engineer. It made quite the bang, too.

In a previous life a company I worked with was incorporating materials into plastic pump casings to improve conductivity which allowed them to be used with flammable liquids.

 

[TugboatEng]

Ed, to elaborate on what you have said about metal support and to touch on fire resistance. Until very recently marine classification societies allowed plastics in certain fuel related applications provided they were protected from direct flame contact. A simple piece of metal below the plastic component was sufficient.

These Racor fuel filters were very common until until subchapter M was added to 46 CFR:

https://ph.parker.com/us/en/marine-fuel-filter-water-separator-turbine-series/751000max10

The new filters have all metal housings and require a water and fuel sensor as you can no longer visually check for water but that costs extra and isn't required under subchapter M

CPVC is gaining popularity for risers and sprinkler piping. It almost meets the A60 requirement fire resistance requirements for marine applications.

 

[LittleInch]

Also don't forget that PE for sure has much higher (x10) the expansion of steel per degree so you need to make special allowance for that.

But basically you need to continuously support it.

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