Typically with PJP groove welds, it has been my understanding that the engineer only specifies the effective throat (E). Based on the welding process that will be used, and other factors, the fabricator would then determine the required depth of joint preparation "S" that will achieve the required (E) dimension. In some conditions, the groove depth "S" and the weld size (E), which is in essence the effective throat, are the same, i.e., the depth of the bevel is equal to the weld size. That's an easy one to understand. However, in the AWS Standard Symbols for Welding...., pg. 30 shows three additional conditions: (B) depth of bevel less than weld size, (C) depth of bevel more than weld size, and (D) square groove, weld size only. I assume that because the bevel depth could be more, or it could be less than the weld size, the letters are used to distinguish between the two.
My question is this: Why would one want a depth of bevel more than the weld size, which may leave an unwelded area within the groove angle at the root? Does the additional groove depth need to be more in some cases in order to achieve the required (E) dimension, even though the root may be unfilled?
Also, if the engineer only specifies (E), how would the fabricator know whether the depth of the bevel needs to be more, or less than the weld size? D1.1 (2.2.5.1) states that "shop drawings shall indicate the weld groove depth "S" needed to attain weld size (E) required for the welding process and position of welding to be used", so, maybe that's the reason D1.1 requires both the "S" and (E) dimensions on the shop drawings. Any thoughts or experiences?
I will answer part of your post, the last part regarding, "how would the fabricator know whether the depth of the bevel needs to be more, or less than the weld size?"
Look at D1.1:2006, page 76, BTC-P4:
- weld size for SMAW is (S - 1/8")
If the design engineer specifies a weld size of 5/8" then,
E = S - 1/8"
5/8" = S - 1/8"
S (depth of bevel) = 5/8" + 1/8" = 3/4"
Generally, you specify a depth of bevel greater than the required weld size because you assume that you cannot achieve full fusion to the "root" of that bevel groove.
That's what I thought..... a few minutes after I posted it dawned on me that the additional groove depth needs to be increased in some cases due to process and position in order to achieve the required (E) dimension, even though the root may be unfilled. Thanks for the confirmation.
I was once told that A2.4 was not a standard for workmanship, only welding, brazing, and NDT symbols.
The construction code is where you will find information on workmanship, processes, etc.
As pointed out by an earlier response, AWS D1.1 has certain conditions that are imposed on the size of the weld based on groove angle. For instance, if the groove angle is 60 degrees or larger, the size of the weld is equal to the depth of the preparation, i.e., groove. However, if the groove angle is less than 60 degrees you have to reduce the weld size by 1/8 inch due to the probability the root will not be completely fused, some slag may be trapped, etc. A conservative approach to joint design, but tried and true.
Different codes have different or similar restrictions.
In contrast to the direction provided by AWS codes, ASME provides little direction that will be useful to someone new to welding engineering. ASME piping codes refer the user to B16.25 that provides some direction on the groove angles, edge preparation, etc., certain joint designs may be prohibited, but in general the user is left to their own devices. ASME isn't going to provide much in the way of direction to anyone that isn't already well versed in welding engineering.
Best regard
Topic American Welding Society Services / Technical Standards & Publications / S and (E) Dimensions of PJP Welds
