Impact Testing

By Lawrence (*****)

Date 10-19-2009 20:55

No data to validate but a thought or two.

For example

SMAW and FCAW processes tend when run vert-up to run optimally in the lower range of parameters suggested by manufacturers for a given electrode diameter. The lower heat input of the range might just have an effect depending on carbon content.

I know there has been discussion of impact values when comparing stringers vs weaves for similar reasons.

It would be interesting if we could get info from somebody working in a testing lab. Pipes get sectioned in various parts eh? While all impacts may be withing acceptable range.. some may be higher or lower..

It's a really good question Jim.

By Jim Hughes (***)

Date 10-20-2009 10:58

Thanks Lawrence. I would like to determine if welding in the vert. position give better impact values over other positions. I have heard it both ways.

Jim Hughes

By js55

Date 10-20-2009 20:35

JIm,
You've heard it both ways because it depends. There are far to many variables to, IMO, state catagorically that one is better than the other. For example, we often hear, and fairly accurately so, mostly in single pass welds, that slower travel speeds, by increasing heat input, enlarges grains, which is generally considered detrimental to impact results. However, slower travel speeds can also increase depth of recrystallization in multipass welds thereby improving impact results. Slower travel speeds can vary the oxide relationship in fluxed process weld deposits and thereby improve impact results as well.
The general industry practice utilizing heat input formulas and maximums is a sledge hammer. There is no replacing actually running tests and getting results, which is why we are still required to actually run tests and get results.

By Jim Hughes (***)

Date 10-21-2009 17:23

js55,
thanks for the input. When running a PQR for P91 material a while back I was told that the 3G position would cause the impacts to be lower than other positions. Now I'm running PQR's on super duplex material and being told that running the test in the 3G position the impacts are going to be higher after getting lower than expected results from running the test in the 1G position. I asked for impacts to be done on the 1G test just for info only.
I agree with what your saying in that there is no replacing running the tests and getting results. I was hoping for a general rule, but as I was told by a wise man years ago the only general rule is "there is no general rule." :)

Thanks
Jim

By js55

Date 10-21-2009 17:58

Jim,
The idea, and supporting data, for the 1G/3G/4G variances for Grade 91 was initiated in the tech literature by Thyssen back in 95. But keep in mind that this position dependent data was also dependent upon bead shape as made clear by Thyssen in their Test Report. They assumed thicker beads in the 3G/4G and thinner beads in the 1G, and this therefore is the primary variable driving the impact toughness discrepency. These types of beads associated with these positions are not always the case. However I would concur that in general thinner beads will result in better impacts for Grade 91 based upon the depth of recrystallization and tempering, especially with Grade 91 where you just can't seem to get enough.
With duplex keep in mind that even though you will get recrystallization from the portion that transformed to austenite (duplex solidifies first as ferrite and then part of it transforms to austenite) you will obviously not have transformation of the ferrite portion and any tempering, so to speak would just be stress relief and perhaps some carbide precipitation, though C is kept low in duplex. You may however see considerable grain growth. Not unlike ferritic SS where you don't have a transformation either. In fact, the ferrite portion of duplex is essentially a ferritic SS, though admitedly it demonstrates some symbiotic thing with the austenite present that seems as a whole greater than the sum of the parts. I don't believe I've ever read the explanation for this. I'm not sure they even know why. Maybe a duplex guru somewhere does.
Duplex does have a rather substantial ductile to brittle transition (due to the ferrite). So thin beads can help Grade 91 but not nearly so duplex, if at all.

By Jim Hughes (***)

Date 10-22-2009 11:27

Thanks again js55. I will keep doing my research and maybe be able to share some data with the forum.

Jim