Hardness of U tube 1

[kpm21443]

We Require A179 U Tube set, where we have specified that Hardness test to be done on the shortest U Bends after Stress Relieving. The Hardness Values obtained are 78 & 74 HRB respectively, noting that the Max Hardness value as per ASTM A179 tubes are 72HRB (nothing Mentioned about U bends)
Can anyone advice on the above and specify any supporting standard/document for reference. Can we accept the obtained hardness of 78 & 74 HRB

 

[EdStainless]

Why did you ask for it if you had no idea of why?
What is the actual hardness outside of the stress relieved area?
A couple of points does not bother me, but you need to decide why it might matter to you.
Did you look at microstructures?
And how accurate is the hardness, taking RB on a tube can have significant errors.

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P.E. Metallurgy, Plymouth Tube

 

[metengr]

What was the stress relief temperature and time for the u-bend? At first review, I would say you did not remove all of the forming strains because SA 179 tube material, on average, is well below 72 HRB scale. Typically 65 HRB scal, on average. You may need to stress relieve at higher temperature to reduce the hardness to the acceptable range. Acceptability will be based on client's end use or their requirement, period.

 

[SnTMan]

Recent job, client requires SA-179 hardness after SR to be 200 B (equivalent) max. Hardness will actually be measured HV10 and converted.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[metengr]

SnTMan;
Was this for a u-bend or weld region? Typically, for u-bend the stress relief is optimized to provide a specified maximum hardness, which may be lower than the hardness from PWHT.

 

[SnTMan]

metengr, actually, this is one of those situations...

Client supplies a spec requiring SR of the U-bend, but without specifying hardness requirement.

The value (200 Brinnel) was selected from an additional spec relating to the specific service. Said spec seems to require no hardness testing for base metals.

Client to review...

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[kpm21443]

metengr, this is u bend, as per ur reply, we understand that u bend is stress relieved to bring the hardness to the required level as per std, but the hardness obtained after stress relieving is 78 & 74 HRB noting that the Max Hardness value as per ASTM A179 tubes are 72HRB (nothing Mentioned about U bends)

 

[kpm21443]

metengr (Materials), Stress Relieving temperature: 610 Degree Celsius, Holding Time: 6 to 10 Seconds

 

[metengr]

The stress relief temperature could have been increased to 635 deg C to reduce the hardness. Again, during qualification of the bending and induction thermal treatment qualification, this would have been sorted out. You may need to re-stress relief at 635 deg C, if possible.