Minimun Preheat Temperature AWS D1.1

Date 11-21-2001 00:43

We have a problem with the minimun preheat temperature for a mild steel. We don´t know what kind the steel is, but the chemical analysis show us that the content of carbon is 0.20%. Mn 0.42%. I think that we won´t have any problems to weld a joint (TC-U5-GF). The thickness is 50 mm. the table 3.2 indicate a preheat of 66 C. However, our client demanded a minimun preheat temperature of 110 C, according with the annex XI (see 3.5.2). The carbon equivalent is 0.28 and the Pcm is 0.23. The practice had show us that for this content of carbon we don´t need to preheat. I would like to know some advices about it. How the Annex XI works? How is the relationship between the preheat calculated (annex XI) with the preheat indicated in table 3.2?

By DGXL

Date 11-21-2001 17:12

I think your client is playing it safe. I have seen base metal and weld metal (post) cracking occur when the preheat/interpass temperature were as specified in Table 3.2. I have some photo's of these cracks someplace, but note that 3.5 specifies that "preheat shall be sufficient to prevent cracking." Looking at Table 3.2 denotes a 65 C or a 110 C preheat depending on the base metal category.

Hydrogen control is critical when working with materials of your thickness. HAZ hardness control would not be applicable to your specified joint configuration (applicable to fillet welds). Depending on the heating method (and gas if applicable) used for preheat, does it take that much longer to preheat at your client's specified temperature? Are these moment frame connections? Annex XI is becoming popular with the structural design community which they feel gives them an extra level of "comfort". I have to agree when I pick up those photos with the WM/BM cracks.