ICE PLUG 1

[ahafeez3131]

In our power plant , at one location we have a ASTM A 106 pipe of size 1 ¼ , sch 80 is running. Water with a pressure of 1550 psig at a temperature of 550 F runs through it. During an inspection when the plant was in shut down state ( pipe having atmospheric conditions and filled with normal temperature water) an ICE PLUG was made on this pipe, with liquid Nitrogen. The liquid nitrogen boiling temperature was -197F. This plug was thawed after two hours. The metal pipe must have seen a temperature close to -197F, at normal temperature and pressure NTP or STP. Now we are moving back to plant start up.
My question is , does this -197F has any effect on the metallurgical properties of A-106 pipe. Does it made more brittle. How I relate MDMT ( minimum Design Metal Temperature) for this condition of NTP or STP.

A.Hafeez

 

[metengr]

My question is , does this -197F has any effect on the metallurgical properties of A-106 pipe. Does it made more brittle. How I relate MDMT ( minimum Design Metal Temperature) for this condition of NTP or STP.

If the correct procedure was used to cool for the freeze plug and warm the pipe, there is no affect on metallurgical properties. During sub cooling, the material will be brittle. However, as long as the pipe was not subject to impact loads, the material will return to original notch toughness behavior. Using a freeze plug is not a normal process condition, therefore MDMT does not apply.

Did you perform a surface nondestructive test of the pipe at the freeze plug location?

 

[EdStainless]

This is often done to expedite repairs.
As Met said, as long as it wasn't damaged while cold there is no issue.
Since you weren't at pressure the design conditions do not apply.

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