Heat Treatment A335 P91 Assistance 2

[rustbuster]

I have some in service steam piping, 9Cr 1Mo V Grade P91 with soft spots. Hardness values ~160 BHN. I am wondering if re Normalizing and Tempering will restore the strength of this material with any success. (Awaiting field insitu replicas as well).

If this is an option, does anyone have ideas on a practical normilizing temperature? In mid shutdown right now with lot's on the go.

Any thoughts / experience would be much appreciated.

 

[metengr]

I am wondering if re Normalizing and Tempering will restore the strength of this material with any success. (Awaiting field insitu replicas as well).

Reply: Yes. The current pipe material hardness is too low. You did not mention how the hardness data was obtained. Field hardness testing must be done using a qualified procedure because surface preparation is vital to assuring accurate hardness data. I have seen so-called soft spots due to inadequate surface preparation (decarburization).


Follow the N&T heat treatment requirements in accordance with the material specification ASME SA 335 Grade 91.

 

[SRPJohn]

Rustbuster, yes it will. I recently went through this exercise. If it is a thick section, I would use forced air cooling.

 

[stanweld]

Yes. We have just done this with excellent results. You must remove the spool section and normalize & temper it in a Furnace. You cannot do it in situ. For best results and to minimize decarburization, heat treating in a protective atmosphere or vacuum is recommended. If the spool section contains welds, you will need to have welding procedures qualified with N&T. We heat treated in a vacuum - forced cooled in nitrogen. I believe that the Heat Treater we used could turn around three spool pieces in less than a week. They have the capability of heat treating spools as long as 35 feet.

 

[rustbuster]

Thank you all so much for your comments. The surface preps are per recommended procedure and the values are true.
You have confirmed my assumptions and I will procede with recommendations with greater confidence. I will also let you know how we make out.

Again this site has proven to be a priceless resource.

 

[rustbuster]

Stanweld,

Have you got a contact or website I could pursue wrt heat treating?

 

[stanweld]

Solar Atmospheres, Hermitage, PA.
Mike Johnson
724-982-0660
mfj@solaratm.com

 

[metengr]

A word of caution, you better make sure that you visit the heat treatment facility because re-heat treatment is not as straightforward as one might believe for this material. I would suggest multiple TC locations on the pipe/fittings for the austenitizing and tempering furnaces or a recent furnace survey and procedure for cooling/handling.

If you can, use one of the reputable pipe fabrication companies that specially deal with Grade 91 piping and fittings. There are a few in the US - Bendtec in Duluth,MN is one that we have used with great success.

 

[stanweld]

rustbuster,
As per metengr, you do need to write a heat treating specification for the work, confer with the heat treater and determine the exact heat treating parameters to be employed and then follow through with surviellance and appropriate testing.