Re-testing frozen process pipe systems 2

[rngrrix]

I am trying to determine if there is a code requirement within B31.3 to re-test piping that had been frozen subsequent to hydrotest. I have performed visual examinations and do not see any deformations.

 

[jrjones]

If you froze a pipe you may way to do some diameter checks to make sure the pipe hasn't dilated significantly. Especially look near any restraints (supports, vents, drains, tees, etc).

Even if you find some dilation, you could probably apply the general 1% rule for out of roundness from most construction codes. If you need to go beyond that have a look at API 579 using the bulging rules and aim to keep the local plastic strains below 5%.

I have, in the past, done another hydro to check the pipe, more for a flange leak check, etc. As long as there is no gross distortion, then a hydro says you still have reasonable properties and you are good to go.

Hope that helps...

Ryan

 

[dcasto]

Interesting thread, I've never looked at API579 for this.

I would wonder if by freezing the pipe and expanding it you end up , pardon the pu, cold working it? I wonder if the metalurgist fourm might be a better resource.

And as always my story. I was rebuild a plant when we came across a bypass line in a wet natural gas service. The bypass dropped straight down, under ground came back up through the bypass valve and into the line.

We had to dig around the by pass line and exposed it. All the coating was broken in longitutanl orientations. We measured the od at 8.7/8 inches to 9.0 inches. The water would drop into the bypass line and sit there and freeze.

I just replaced with a slightly off level bypass.