I have a few questions about compound weld joints. First, what is the main reason for using them? Secondly. I have seen a few diagrams that show the 37 degree portion of the weld extending upwards for 3/4", and the remainder of the weld is at a 10 degree angle. So does this mean that the 37 degree portion of the weld has a fixed height of 3/4" and the remainder of the weld (regardless of thickness) is at 10 degrees?
Here is a diagram that I have been looking at: http://www.globalspec.com/RefArticleImages/8DE033B4047F3F210EE55EDEB387249B_2_CH02_54.gif
00:38 Jan-17-2010 Juan Amado Engineering, Inspection Arco Industrial, S.A., Panama, Joined Nov 2001 44
Re: Compound weld joints (37-10)In Reply to David Bunch at 21:03 Jan-16-2010 (Opening).
The main reason for using such joints is to minimize the amount of weld metal to be added to the joint. This creates savings in time, weld metal, labor, energy and measures to prevent distortion. This savings must offset the cost of preparing such a joint, which are higher than creating a conventional straight bevel.
The 3/4" dimension, at which the angle of the bevel changes direction, has to do with the fact that at that point the 37.5 angle has created enough of an opening to be able to access the joint with the welding process to be used. This dimension, however, is not written in stone, you should be able to create a joint that is appropriate for what you are doing, but I think you will find that in many cases it will be a nice size to work with.
As Juan says, on thick material access is required to put in the root, hence the bigger included angle for the bottom 10 - 15mm. Once sufficient access has been made the narrower included angle 6 - 10 degrees requires less weld metal, less runs and potentially a sounder joint.
The compound bevels and the J-bevel are a principal reason for the drive to encoded UT, a combination of automated or semi-automated PA, TOFD and PE. Tandem and zonal discrimination techniques may be required for the steep fusion faces.