Can CE be used to Determine Interpass Temp?

Date 04-02-2008 20:32

Have been preparing for an AWS D1.4 weld procedure qualification using ASTM A706 #8 rebar. The certified MTR tells me that the CE is 0.523. By AWS D1.4 Table 5.2, I have a very low preheat temp requirement (50 deg F). This is good for me and the upcoming production. I cannot find any information regarding interpass limits. Footnote b of this same table only says "shall be sufficient to prevent crack formation". What do I do with that nugget of fine information?

In preparing for our PQR, we have discovered our rebar is quickly reaching 500 deg F within 3 inches of the joint ( joint is CJP double bevel tee joint). So we shut down, wait till temp drops a bit and continue. This will be bad for production - CAN ASTM A706 TOLERATE HIGHER INTERPASS TEMPS???? If so, or if not, is it related to CE in some calculatable way?

Thankyou please.
Tom

By hogan

Date 04-02-2008 20:51

because this is a pqr you are allowed to do whatever you can prove through testing (almost). maybe try one without allowing it to cool between passes and test it.

By Fredspoppy (**)

Date 04-03-2008 13:14

I don't have a copy of D1.4, but from D1.1 I would suggest that the preheat/interpass minimum would be quite a bit higher, with a lot depending on the hydrogen level of the consumable you plan to use, restraint level and base thickness. Check out Appendix XI, Tables XI-1 and XI-2.

By tom cooper (**)

Date 04-07-2008 17:13

Fred-
Your reference to Appendix XI tricked me! Fortunately I found an old (1990) copy of D1.1 and saw what you were intending. This is now Appendix I in 2006. By this method, my weld would be in "Zone 2", i.e., CE = .523 & C = .280 which then means I should use the Hardness Control method, except that my weld is a groove weld which then means I must use the Hydrogen Control method; by Hydrogen Control, I am in the Susceptability Index of F at most; for low restraint and Susceptibility of F, I should have a preheat AND interpass of at least 280 deg F.

Perhaps I misunderstand the meaning and intent of "interpass temperature".

By "required interpass temperature", am I to wait until material cools to 280 deg F before resuming the next pass? Why? Higher base metal temps are conducive to lower cooling rates, which I thought would be preferable to minimze quench hardening effects.

I understand that in PQR mode I can do anything that allows me to pass destructive tests, but am looking for basic understanding of "interpass".
Thanks

By hogan

Date 04-07-2008 18:04

the interpass requirement is a minimum. not a max.

By Fredspoppy (**)

Date 04-07-2008 18:34

My reference was the 2002 Code. That is the electronic file copy I have and didn't check the latest hard copy. Minimum interpass temperature is the same as preheat and, in many Code applications is dictated by the applicable Code you are working with, although the actual qualified can be above the minimum required by the Code. Maximum interpass temperature is normally whatever you qualifiy with due consideration taken, according to the materials you are qualifying. Higher isn't always better.

By Kix

Date 04-03-2008 15:22

What Hogan means is that you can use whatever interpass temp you want as long as you qualify it by testing. If you weld it up without stopping to let it cool and your tensiles come out within the limits of the base material, then you are good to go.