Heat Treating X70M Pipe after Hot Induction Bending to pass Yield Strength 1

[shattersys]

Hello,

I am trying to determine heat treat parameters for 30",0.500"w, X70M pipe after hot induction bending to bring the yield strength to acceptable levels per API5L. The temp used to bend the pipe is between 900-1040°C with water quenching.

After bending without heat treatment, the Extrados and Intrados failed yield strength and had average through thickness hardness of about 220 HV.

I have tried the following heat treatment parameters without success:

Free heat to 316°C
316-480°C at a rate of 100°/Hr
30 min soak at 480°C
Air cool


Any suggestions to bring the yields up through tempering?

Many Thanks,

 

[weldstan]

What is the chemistry? And you will not be able to increase the yield through tempering.

 

[shattersys]

See attached chemistry. If tempering won't increase YS, what do you suggest?

 

[weldstan]

You may not be able to resurrect the YS because the YS was originally due to thermal mechanical processing (most likely). I would try re austenitizing at 1675 F and water quenching followed by tempering at 550F for 60 minutes. Unfortunately, toughness properties may well be adversely affected.

You needed to clue the mill in that you were going to induction bend their pipe to make bends and to guarantee YS after bending. They could have compensated by increasing carbon content and micro-alloying.

 

[shattersys]

Thanks for the reply. Unfortunately the client specifically requested X70 30" bends. Market ability also plays a factor. It seems everything is TMCP.

 

[LittleInch]

I've seen bends having to be made at X60 or lower with thicker wall before due to this issue.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[weldstan]

Ditto LittleInch, induction bends in X60 and lower grades are commonly done.