Why does D1.1 (2010) list A36 in both Grp I and II but B2.1 (2009) lists it as only Group I?  Also, A572 Gr.50 is a Group II in D1.1 and a Group I in B2.1.  What gives?

A

Different committees, different philosophies.

AWS B2.1 is heavily influenced by ASME where A36 is considered a P1 Grp. 1 material. If you are working with B2.1, you are most likely qualifying the WPS by testing in accordance with that standard. If toughness is a contract requirement, it will have to be considered. If PWHT is required, it will have to be considered. In other words, you will essentially qualify the WPS just s you would if you were working to ASME Section IX. The WPS you qualified by testing has demonstrated it meets the requirements of the welding standard, thus it matters little if you used a non-low hydrogen SMAW electrode or one that is low hydrogen. 

AWS D1.1 includes A36 in two groups for the purpose of developing prequalified WPSs, i.e., no testing is required if all the conditions prescribed in Clause 3 are met. The matching filler metal used for A36 is dependent on the thickness of the base metal. If it is less than or equal to ¾ inch, a non-low hydrogen SMAW electrode can be used and still be considered prequalified. However, if the base metal is more than ¾ inch thick, a low hydrogen SMAW electrode or welding process must be used if the WPS is to be considered prequalified. The major advantage of meeting prequalified status per D1.1 is the savings in dollars and time. 

Wait there is more; if prequalification status is the goal, one must consider the minimum preheat requirements which are dependent on a couple of variables, one being whether low hydrogen requirements are met and the other is thickness. If a Category 1 base metal is joined with non-low hydrogen SMAW electrodes, higher preheat is generally required for the same thickness of base metal selected from other than Catergory 1 and welded with low hydrogen electrodes or process. 

When comparing Tables 3.1 and 3.2, it can appear there is a disconnect with regards to preheat. Table 3.1 appears to limit the thickness of A36 to less than or equal to ¾ when welding with non-low hydrogen SMAW electrode. This is the case, however, there are more materials listed in Table 3.1 than just A36. The other listed materials listed in Group 1 are not limited to the thickness limitations applicable to A36, thus they require higher preheat per Table 3.2 when they are welded with non-low hydrogen SMAW electrodes. As it happens, whether the A36 is listed in Group 1 or 2, the preheat is the same for ¾ inch or less when looking for A36 in the Categories (A and B) listed

엘리스