Purpose of machining land in NASA STD 5006

[kevlar49]

NASA STD 5006 para 4.5.4.1 Welding Techniques: Class A and B joints:
Joints which have prepared grooves form one or both sides (reference Figure 2 and [C]…shall have a weld land which is completely penetrated on the initial pass. Partial penetration welds from one side are permissible provided the opposite side is machined into the penetration root prior to completing the weld.


What is the purpose of machining the opposite side of weld for partial penetration welds?

 

[gtaw]

It is called back gouging by most welding standards.

When a double sided joint requires complete joint penetration back gouging the second side to sound metal is intended to ensure the weld completely penetrates the complete cross section of the joint. The first side is welded to completion or partially depending on the groove depth. The second side is then back gouged by some suitable means to a depth that ensures any unfused material in the root of the first weld is removed. The second side of the joint is then welded.

Best regards - Al

 

[kevlar49]

Would I need to back gouge edge welds (e.g. joining of two edges of bellows segments)? Example of edge weld that I am referring to

http://www.google.com/imgres?q=edge...05&start=0&ndsp=53&ved=1t:429,r:34,s:0,i:193.

Would this actually be a full penetration weld?

 

[berkshire]

Kevlar49,
I think you will find that a fusion weld on a prepared edge is considered a full penetration weld as long as the speed and feed is correct.
The danger with this kind of weld is a shallow weld, not achieving full ( i.e. to the depth of the metal ) penetration, and a subsequent crack starting from inside the weld.
However I do not think that is the intent of the back gouging standard.
B.E.