Heat treatment for C/S Line Pipe Induction Bends

[nickt1960]

We are procuring line pipe and bends out of Japan. Material is Dnv-OS-F101 Grade 450 (X 65 equivalent), seamless 4" diameter x 7.4 mm wall thickness. The line pipe undergoes a Q & T during manufacture. The mother pipe that is then used for induction bending may or may not be put through post bend stress relief heat treatment. However, in X65 material I am aware that heat treatment usually results in a drop of impact and tensile strength. I am not sure what benefit the HT would give us in thin wall material such as this. Any opinions on whether we should waiver the post bend heat treatment?

 

[metengr]

I found information from a GE Energy web site

http://www.gepower.com/prod_serv/serv/pipeline/en/about_pipelines/pipe_prop.htm

that specializes in pipeline integrity management.

Regarding induction bending of API 5L line pipe;

<<Induction Bends
An alternative method of producing pipeline bends is the induction bending process. In this process, a length of pipe is gripped at one end by a clamp which is attached by an arm to a pivot point. A hydraulic ram pushes the pipe through an induction heating coil and local deformation takes place in the coil, so the emerging bend follows the arc dictated by the movement of the clamp at the end of the clamping arm. The material is water quenched immediately so deformation is restricted to the short heated area within the coil.>>

Looks to me that with induction bending process described above you will need to temper the material that has been locally heated by the induction coil and subsequently quenched by water, otherwise your mechanical properties, especially toughness, will not be consistent along the bend radius.

Does this sound familiar to what you anticipated? If so, you need to consider a post- induction bend tempering heat treatment. I would select a tempering temperature that is 25 deg F below the original tempering temperature for the line pipe to avoid affecting the bulk properties.

 

[nickt1960]

Yes, I didn't consdider it to be a temper treatment, that makes more sense than a stress relief. Translation problems!
Many thanks

 

[stanweld]

Induction bending has been performed on arctic grade X-65 line pipe for over 25 years. We developed parameters for heating to the normalizing temperature, quenching during the bending process followed by tempering. Full mechanical testing in four circumferential quadrants and along the longitudinal bend radius was done to confirm strength and toughness at -50F. I would recommend that you do the same for a test bend on your production pipe if your induction bend manufacturer cannot provide similar test data from similar production X-65 materials.