2 replies to this topic

[justinbasha]

Hi everyone:
Just wanted to start off by saying what a great site this is an keep up the good work. Very informative. I was alway curious why went hydro testing piping systems it is alway suggested to hydrotest piping to the flange rating not piping rating?


Thank you in advance for all you help

Justin

[Art Montemayor]

The flange joint is the weakest part of a piping system.

[paulhorth]

Justin,

I am puzzled by your question.

If you are talking about a new plant design, the hydrotest pressure for every piece of piping is specified in the line list, not "suggested". This entry is added by the piping engineer and is derived from the Design Pressure for that particular line in accordance with the relevant piping code. The Design Pressure is set by the process engineer based on operating conditions, and is always less than the flange rating. But, when multiplied by the test factor, (say 1.5) the hydrotest pressure can be above or below the flange rating.

 

For example:

A section of process piping may have an operating pressure of 20 barg.

The process engineer will enter a design pressure of say 23 barg, based on operating variation plus a margin of say 10% as laid down in the client's design philosophy, and this will determine the set pressure of the PSV protecting this system. This design pressure is entered in the line list against every line in this system.

This piping system will have 300# flanges which have a maximum pressure rating of around 41 barg depending on design temperature, because the pressure is above the limit for 150# flanges..

When the line list is updated to AFC status,the piping engineer will add the hydrotest pressure, say 23 x 1.5 = 34.5 barg which is still below the flange limit.

 

There is no need to test up to the flange limit. For example, a flare system will have 150# flanges which have a rating limit of about 19 barg, but the design pressure would typically be much lower.

 

Paul