Cleaning or Peening?

By swnorris (****)

Date 04-15-2005 11:00

Hi Scott,

It sounds to me like the welders progressed from cleaning to peening. Although 5.27.1 clearly indicates that lightweight vibrating tools are not considered peening, which is probably due to the low impact, I'd call it peening if its that excessive. Even at low impact a weld can be peened with the scaler if you stay on a certain spot long enough. In Jefferson's Welding Enclycopedia, which is an AWS publication, peening is defined as the process of repeated blows to the surface of metal. The blows may be administered manually, as with a hammer, or with pneumatic tools. Here's something you may want to consider: Is it excessive due to the welders using a higher air pressure on their needle scalers on the hot welds? There's a recommended operating air pressure for these tools. If they exceed that, it could possibly cause the problem you describe, but It almost sounds like the welders are using the needle scalers to try and blend in and hide the starts and stops on the weld face.

By jwright650 (*****)

Date 04-15-2005 11:48

Even when peening is allowed, it describes it as "local plastic deformation", which it definitely sounds like what you are describing.
And it goes further to state that such peening "shall always be done after visual inspection", and be followed by MT as described futher in this paragraph. [ref. AWS D1.1:2004, 2.20.6.6(3)]
I had found a couple welders several years ago in our shop trying to hide porosity by beating their weld to death. There may be another reason they are working so hard to clean their welds. Most guys aren't going to spend the energy and time cleaning that good, I can almost guarantee it.

John Wright

By gerold

Date 04-15-2005 13:03

It sounds like caulking (Plastic deformation of weld and base metal surfaces by mechanical means to seal or obscure discontinuities.) to me which may be prohibited depending on your material, circumstances, and engineer approval. (AWS D1.1-2000 Para. 5.28)

Chris

By bamaCWI (**)

Date 04-15-2005 19:01

Thanks for all the replies. A visual was performed before cleaning and all welds were acceptable. However I requested that less deformity be created by this process. They were told, that this degree of "cleaning" was necessary in order for the weld to obtain proper coating of zinc during the hot dip process. The base material was A500 B.

Would these areas of aggressive "cleaning" be more susceptible to cracks during the hot dip process?

By jwright650 (*****)

Date 04-15-2005 19:44

Actually with that type of wire you'll need to get it ALL off before dipping, or it won't stick. I think as long as the welds are clean they should be OK. In the past, I've had some of our hotdipped come back and look like crap because they didn't get all the slag cleaned off. Shouldn't have to beat it into submission for hot dipping though.
John Wright

By jwright650 (*****)

Date 04-15-2005 19:46

[quote]"The base material was A500 B"[/quote]

Be sure to inspect these closely with MT after dipping if they are heavy walls. I had several pieces of 5/8" wall split (open on both ends) after it was hotdipped.
John Wright

By CHGuilford (****)

Date 04-18-2005 16:54

The degree of "peening" that has been described is not needed for galvanizing. Steel is pickled to remove mill scale and foreign material and to etch the surfaces prior to dipping into the zinc bath. Anything that will prevent the caustic and acid baths from working properly (heavy grease, paint, weld slag, etc.) should be removed first, but other than that, nothing else is needed.
Galvanizing is an iron/zinc alloying process so a profile is not needed; unlike paint that needs a mechanical attachment to the surface.

Needle guns and air-chippers are used as a de-slagging time saver, but if they must be used to get difficult slag off, then you might want to look at the welding technique and parameters. Slag doesn't normally come off hard unless there is something wrong.

Stress raisers created from peening could cause problems depending on locations, but what you are describing doesn't sound like it would cause difficulties. Be advised though, I have seen 3 foot lengths of 6 x 6 x 1/4 A500 tube split open like a burst shotgun barrel. There were no plates or restrictions of any kind on the ends to cause the splitting. We never learned why, and the replacement pieces had no problems. Most galvanizing is trouble free, but strange things do happen.

Chet Guilford