Piping Freeze Plug Installation Experience / Guidelines

[bosse1950]

Gentlemen - we are guiding our client on the installation of 3 freeze plugs (1 - 30" & 2 - 24")on an existing (25+ year) offshore platform. I am looking for technical data / experience in relation to metalurgical dangers (during application & post application) which could occur during the application of Freeze Plugs to carbon steel piping / welds / etc. Liquid N2 will be used for cooling medium. We have set up meetings with a specialized contractor & consultant, but any independent data would be helpfull.

 

[0707]

"The cold nature of nitrogen, particularly cryogenic nitrogen can affect some materials detrimentally. Materials such as carbon steel lose ductility and become brittle and shatter under stress. Tensile strength increases at low temperature"

The impact test of the pipe material should be checked to see at what lower temperature its values are safe.

luismarques

 

[jte]

bosse-

ASME PCC-2, Repair of Pressure Equipment and Piping has an article (3.2) about freeze plugs which might be useful.

http://catalog.asme.org/Codes/PrintBook/PCC2_2006_Repair_Pressure.cfm

The sizes you are contemplating are larger than I've seen (~10" NPS max) but probably doable provided that you can absolutely stop all flow and maintain that condition while the plug is being formed. The slightest trickle can keep a complete plug from forming. If you are changing out a bolted fitting (flanges) replace the studs/nuts with new, well lubed ones prior to the freeze plugging operation to minimize the likelyhood of any issues from breaking the flange. Keep the plug location as far away as reasonably possible from the work and from any other sources of impact (rotating equipment, other construction jobs nearby or above - though nobody ever drops a wrench...). Avoid locating the plug on/near a circ weld seam. Be sure to pressure equalize both sides of the plug prior to beginning the thaw-out - nothing like an ice slug in your pipes to wake you up...

jt