Hydrotest of GRE pipes 2

[HHB]

Hi all,

I have received an Inspection Certificate prepared by a TPA company that shows a hydrostatic test (with a test pressure of 30 bar for a duration of 5 minutes) has been conducted on a series of GRE piping materials with PN 20.
Based on which standard are we allowed to apply a pressure 1.5 times greater than the maximum pressure that the pipe material can withstand?
How is it still a Non-destructive Test?

Any comments would be appreciated.

 

[SJones]

API 15HR, ISO 14692-2 - the standard used should be stated in the inspection documents. Remember - the pressure rating is achieved by factoring down the qualified pressure; it is not the absolute maximum pressure that the material can withstand.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

 

[europipe]

never heard of PN20

 

[LittleInch]

You need to understand the difference between the long term rated pressure that a thing can withstand (in your case the PN rating) with the maximum pressure it can withstand before it breaks / ruptures. Normally a factor of safety is involved which typically for pipe and piping components is at least between 1.25 for steel pipeliness to 1.5 for pipe and components. Therefore as a test, the test pressure is commonly 1.5 x max long term rated pressure for pipe used in plants, valves etc. This includes GRE pipe.

The idea is that the material is tested to just below the point where it would suffer any damage such as cracking or yielding, but higher than any pressure it would see in its operating life.

The actual test pressure varies according to materials and use and hence the code given by SJones will provide that pressure for GRE. Other materials may be higher or lower fraction of the maximim rated pressure or design pressure.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[SJones]

Those two standards indicate 1.5x pressure rating, or 0.89x qualified pressure if it is lower in the case of the ISO.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.