Hello again,
First thank you all for you're responses on my last query. This time I'm having a debate on peening, during a qualification test and in production. The root of the issue is needle guns. Is using them considered peening or are they a light vibration tool?
Thank you for your time and consideration in advance.
Scott
Hello Scott, the answer to that likely lies more in the operators use of the tool. If they are camping on it and giving the weld a golf ball texture then I would say that it could be considered peening. If the tool is simply used to knock off the slag and possibly some spatter I don't believe that you could consider it "peening". A visual observation on an inspectors part will likely determine whether it has been abused or not. But that's just my personal observation to your question. I am sure others will have opinions/suggestions to additionally address your question. Good luck and best regards, Allan
Peening, as it relates to qualification, would be performed as a method of stress releiving, which is not required on all materials and is most often performed through various types of post weld heating and slow cooling.
Using a needle gun, as it relates to qualification, would be a means of weld cleaning only, and can be specified on the WPS, especially for interpass cleaning.
Tim
By Superflux 
Date 05-11-2012 17:36
Edited 05-11-2012 17:42
Peening according to AWS is "the mechanical working of metals". When you compare that with the usages for peening and definitions used by other organizations I don't believe you can peen with an air needle scaler. Especially if you don't 'work' the metal after the slag is removed. By which time the weld metal would be cool enough it would be difficult to do. Peening takes a certain amount of force and size of striking object (ball peen hammers).
Peening as described in section 5 of D1.1 does not restrict one from using a needle scaler to remove slag though I have had inspectors who insisted it did. Look closely at Section 5.27 and 5.27.1 as well as the Commentary for that section. The reference is used to describe working the root or surface metal (see above definition) to mask discontinuities such as undercut, porosity, etc so the inspector can't see them during VT.
Have a Great Day, Brent
AWS 3.0 (2010)
Peening- The mechanical working of metals using impact blows.
Caulking - Plastic deformation of weld and adjacent base metal surfaces by mechanical means to seal or obscure discontinuities.
Thank you all for your responses, very helpful, and I'm now winning the debate. But its hard to win quality over production!
Peening involved sever plastic deformation of the entire weld bead cross section.
Aggressive use of the needle gun (even those that use a chisel like tool) is not going to affect the entire cross section of the weld bead. While it may obliterate the ripples of the weld bead surface it is not sufficient to cause the cross section of the weld bead to be plastically deformed.
In the case of D1.1, it is clear that the use of tools typically used to remove scale and slag are not considered to be peening.
Al
