Hardness T22 after cold bending

[xgiorg]

Hi everyone,

I want to know if you would apply a Heat Treatment after cold forming a 51mm x 4mm SA-213 t22. The tube is U bend with a radius R = 50mm. I have measured the hardness in 20 bends: Max:201HB and MIN:97HB.

Whe are using asme VIII Div.1.

Thanks.

 

[stanweld]

Was the min hardness 97 HB or 197 HB? 197 to 201 is well within the accepted range for the material. 97 HB would indicate strength well below the minimum specified tensile strength of the alloy - I don't belive it is possible to achieve such low strength from the alloy. SA-335 limits hardness to 220 HB max.

 

[stanweld]

Regardless of hardness, ASME VIII provides mandates for stress relief after cold bending based on percent strain.

 

[metengr]

There is no Code required post bend thermal treatment for T22. This is a workhorse tube material for ASME Code applications. What stanweld mentioned is applicable to shells and heads for ASME Section VIII, Div 1, not tubing. Regarding the hardness, assuming a corrected lower value as mentioned above, this is typical for post formed T22. I would perform a post bend nondestructive test of the extrados as a minimum for a percentage of total u-bends, or do all of them.

 

[stanweld]

Another Senior Moment! My brain saw P/T23 instead of T22 (don't know what my eys saw) and my hardness quote was from SA335 for P23. By the way, what was the hardness in the non-strained tubing and is the material in a stress corrosion cracking service?

 

[xgiorg]

Thank you very much for your opinion, but I have more questions. About the heat treatment. I have asked a workshop that makes heat treatment and they said to me I have to make a normalising of the bends (30min). I saw in epri specification for 22 grade material:

http://my.epri.com/portal/server.pt...D=000000000001012840&RaiseDocType=Abstract_id

there is a table (T-1 p.73) that shows a recomended method of heat treatment.
What is better for this material?
Also I have read in this forum about heat treatments of 10-15 sec duration with 100F/sec. But I don't remember where (sorry). Do you know something about this method? What do you think?

 

[metengr]

xgiorg;
A T22 U-bend does not require a post bend thermal treatment per ASME Section VIII, Div 1. IF you do want to perform a post bend thermal treatment, it should be done following the recommend post weld heat treatment requirements to reduce the hardness. Normalization is NOT necessary or required for this material.

For T22 tube material;

Heat the u-bend region to 1250 deg F min (normally 1250 deg F to 1375 deg F).
Hold at 15 minutes at temperature, air cool.

Induction heating of u-bends is common practice. Also, if you are using a shop for this activity, I would ask them to provide a procedure and make sure this procedure has been qualified for use on T22 tube material.

 

[aniseng]

metengr,
why do you recommend such a long holding time ?
What if you adapt the holding time in order to reach the hardness requirements of this grade (85HRB) ?

xgiorg,
what is the application for such a u-bend tube ?

thanks in advance.

 

[metengr]

aniseng;

why do you recommend such a long holding time ?

Because using a conventional furance for thermal treatment of u-bends, 15 minutes has been used and was appropiate from a qualification standpoint.

What if you adapt the holding time in order to reach the hardness requirements of this grade (85HRB) ?

This is acceptable. Induction heating will also shorten the time. As I mentioned, post bend thermal treatment requires a procedure that has been qualified using thermal treating equipment that will be used for the u-bends.

 

[xgiorg]

Aniseng, this is for a 48 bar 260ºC heat exchanger.
Tomorrow I will decide what to do, but it seems its not a critical point due to hardness is below the max for this material. Why it can be a stress corrosion cracking? Hydrogen sulphide? in this case it will work with water inside and flue gas outside(no SO2 in the gas, 3.36CO2, 13.41O2, 74.83N2, 7.5H2O, 0.89Ar). Thanks a lot everyone.

 

[xgiorg]

Finally I told to the workshop to make the bends without a post Bend Heat treatment, but amazingly, they make it. They have aplied a 925ºC 30min, with heating rate: 180ºC/h (unrestricted heating rate to 300ºC) and air cooling. I know this is not your recomendation. That's why I want to ask if it's ok, because it's my responsability to accept the material. What do you think? In my opinion the microstructure and the grain size will be ok, but I would like to make a hardness test before to make conclusion. Thanks in advance

 

[metengr]

xgiorg;
This is a re-heat treatment of the bends based on the temperature you provided. Yes, a hardness should be performed along with dimensional checks on a sampling of the bends for conformance with SA 213 and SA 1016.