Pre-heat

Date 02-03-2007 15:56

Mark,
If it's ASTM A36 2" thick, I believe everything is fine if they preheated to 300F, the figures listed in Table 3.2 are minimums. No worries, unless they got carried away and exceeded 1200F.

Note that A36 shows up in Cat A (A36 2" = 225F) and Cat B (A36 2" = 150F), but the difference is whether they used SMAW Lo-Hy or not(read the notes).
Also note that the preheat is dependant on the thicker of the materials to be joined. (plate?beams? whichever is thicker)

By MDG Custom Weld (***)

Date 02-03-2007 16:11

Thanks John!
I used the 150F because it is a CAT B weld, using FCAW.
This 2 inch is the thickest, the beam is 7/8, or 1, I don't remember.

On a side note, does the beam need to be heated too in this application since the member is?

By jwright650 (*****)

Date 02-05-2007 11:37

Morning Mark,
Yes, you would heat the entire joint at the point of welding(both thick and thin)....you would check your preheat with a tempilstik at a minimum of 3" from the joint on the thicker part(this is so you can verify that the heat has soaked into the thicker piece and the thicker piece won't be acting as a heat sink and cool the weld too quickly).

By hogan

Date 02-05-2007 16:25

i've found the infared temp gauges work great for this. the price has come down a lot also. just got a new - 100degree f to +2000 degree f for $60.

By 803056

Date 02-07-2007 04:29

Be aware tha the IR thermometers are based on black body radiation. Materials like aluminum, stainless steel, nickel, etc. can give readings that can be off by 125 degrees F or more.

Bob Wiswesser did an article for the WJ or Inspection Trends where he gave some of the problems he encountered when comparing the different methods of checking preheat and interpass temperature.

Al

By Bill M

Date 02-07-2007 15:10

Al,
I was not aware of the temperature issues you described and would like to learn more about it.

Do you know by chance, what issue that article was in?

Thanks!

By MBSims

Date 02-08-2007 04:29

Here's some related info on emissivity that should help you understand the reasons for error:

http://www.openxtra.co.uk/articles/emissivity_intro.php

By 803056

Date 02-08-2007 21:19

I'm sorry, I don't remember when I read the article. I believe it was last summer in Inspection Trends.

Best regards - Al

By CHGuilford (****)

Date 02-10-2007 03:23

I don't know of any articles offhand. What I have experiened is that some infra red thermometers will indicate a PQR plate is below the temperature is lower than 400 deg F but a 500F tempstick was melting. The tempstick was properly labeled and several others with different lot numbers would also melt. When accurate temperature measurement is critical, I like to use temp sticks. For informal use, I use the infra red units.