ASTM A992 PWHT

Date 12-12-2005 23:42

Not exactly an answer to your question, but the first thing I would do is ask the inspector to show where in the specs or contract this is required.

For what it's worth, requirements for A 992 shouldn't be any different from requirements for A 572 or A 36.

Hg

By QCCWI

Date 12-13-2005 00:18

I hope that 3rd Party Inspector stays in your part of VA.Down here in Southern VA we do not need him.

By jwright650 (*****)

Date 12-13-2005 01:38

Now it seems they are not really asking for PWHT but they are concerned that the Group 4 columns will crack after welding if we don't let them cool at a controlled rate by adding heat to them after the welding is completed to slow the rate of cooling due to the cooler winter weather.

Is there info somewhere stating how this should be done properly?
John Wright

By MBSims

Date 12-13-2005 04:38

I'm not aware of a continuous cooling curve for the A992 steel, but suspect that if proper preheat is used for the thickness to be welded, then the cooling rate would not be fast enough to form martensite when welding is complete. You could have a local lab or university perform a Jominy test to determine the cooling rate needed to produce an unacceptable hardness level and make sure your cooling rate does not exceed that rate. If you can't find anyone to do the test, let me know and I can hook you up with someone that has the equipment to do it. They would need some 1 inch diameter x approx. 4 inch long test bars from the A992 material. Here's a link to some info on the test:

http://www.doitpoms.ac.uk/tlplib/jominy/jominy.php

http://www2.umist.ac.uk/material/research/intmic/features/jominy/notes.htm

By jwright650 (*****)

Date 12-13-2005 11:12

"I'm not aware of a continuous cooling curve for the A992 steel, but suspect that if proper preheat is used for the thickness to be welded, then the cooling rate would not be fast enough to form martensite when welding is complete."-quote

They were my thoughts exactly, here in the shop I can monitor the guys and make certain enough heat has been kept in the part before and during welding, but I'm afraid that the erector and his men are the ones we'll have trouble with. I'll get with our field representative and see if he can help me with the monitoring in the field. Meanwhile, I want to get into those links that you provided and study up.
Thanks for your help,
John Wright

Edit: Marty, C3.5 basically states what you and I were thinking all along, when sufficient preheat is used, the cooling rate will be slowed enough to produce a crack-free joint.

Edit#2: also maintaining sufficient interpass temperature between passes when it cold on the jobsite.

By swnorris (****)

Date 12-13-2005 11:52

John,

I copied part of my response to a November posting on weld shrinkage in jumbo shapes. There is a link to a great article at the end that may be helpful:

Welding Group 4 and 5 shapes definitely require some special attention. These are generally in compression as columns. These heavy sections have been known to exhibit segregation and a coarse grain structure in the mid-thickness region of the flange and the web. Because these areas may have low toughness, cracking might occur as a result of thermal cutting or welding. To minimize the potential of brittle fracture, the current AISC ASD Specification includes provisions for material toughness requirements, methods of splicing, and fabrication methods with an element of the cross section more than 2" thick intended for tension applications. You might want to refer to that if you have access to a manual.

The Challenge of Welding Jumbo Shapes

http://www.jflf.org/pdfs/papers/jumboshapes.pdf

By jwright650 (*****)

Date 12-13-2005 12:12

Scott,
I did find J1.7 in the ASD 9th edition and that J2.7 Preheat for Heavy Shapes recommends a preheat of 350f min. for materials over 2" thick. But hasn't the Table 3.2 in D1.1 been revised since this ASD manual(9th edition) was published?
John Wright

By swnorris (****)

Date 12-13-2005 12:33

Yes, Table 3.2 has been revised. There are other jumbo shapes references in AISC publications with regard to preheat. I just glanced through them, but I didn't see anything that addresses post heat: LRFD Vol. 1 pg 6-27 1c, page 6-70 J1.5, 6-71, and 6-164 1c. Also Manual of Steel Construction Vol II Connections, page 2-22. Have you talked to the EOR and conveyed the concerns about PWHT to him? It might be something he may have overlooked, or maybe he evaluated it and decided it would not be required.

By jwright650 (*****)

Date 12-13-2005 12:45

I talked to our field rep a few minutes ago and conveyed to him that with sufficient preheat and maintaining the interpass temps during welding (making sure the welder checks before each addition pass and adding heat if necessary) should allow the sections to cool at a rate that would be slow enough to prevent cracking or a brittle HAZ. If they heat those sections and check the heat at a minimum of 3" either side of the joint at the thickess point of welding, I'm sure they will have enough heat to slow the rate of cooling even in 16F weather with a breeze blowing. What I'm worried about is the thinner sections 1/8"-3/4" with a simple fillet weld on them in those conditions, although the inspector didn't mention those.
John Wright