Q: Are there problems indicating a partial flare bevel weld to be used with a concave profile? Should this even be done? The rational is that the joint needs to be flush for fit up of secondary pieces. I am concerned that indicating such a profile will lead to weld cracking due to the shrinkage stresses. Any comments or ideas you have would be greatly appreciated.

A: Specifying a concave bead could be problematic. Concave beads do tend to be crack sensitive, and are subject to "hot cracking" during solidification and cooling. Additionally, flare bevel groove welds tend to press the limits on the width-to-depth ratio (e.g., they tend to be deep compared to their width) and this promotes cracking as well. So, your concerns are appropriate.

It should be possible to specify a flat faced groove weld, or even one with a slight convexity, so long as the joint is not filled totally. Assuming that the required throat dimension can be achieved, an under-filled flare bevel groove weld should be fine. Also, excessive fill can always be ground off.

I suggest you carefully communicate your intent on the drawings, allowing some under-fill (again, assuming the design can tolerate this condition) and allowing for grinding if necessary to correct for overfilling.

Q: I was wondering if you could give me a brief explanation as to why it would be necessary to weld aluminum with the GTAW process, vertical up progression and never down. Also, would this be true for the GMAW process?

A: It is always recommended to weld aluminum vertical up, instead of vertical down, regardless of the welding process. This is because vertical up welds in aluminum are less prone to contain porosity than vertical down welds.

When welding round objects, with rotation (1GR position), welding with a vertical up progression means that you have to put your torch on the "aftertop-dead-center position" when considering rotation direction. This is opposite of what you would do with steel components, and that is a common application detail that often is overlooked.

Q: We are welding X70 pipe and would like to know what rod you would use for the root pass, E6010 or E8010? Our concern is that the E6010 yield strength is not as high as X70 pipe. Also, would we need to do a post weld heat treatment or controlled cooling?

A: For matching strength girth welds on X70 pipe using cellulosic stick electrodes, we recommend using E6010 for the root pass and E8010 for the fill passes. Essentially, this filler metal combination under-matches the root so it does not crack, and overmatches the fill to obtain the required strength.

Preheat and interpass may be recommended depending on the electrode, pipe size, actual pipe strength, chemistry and other requirements (NACE, etc.).

Post weld heat treatment or special cool down procedures usually are not required.

Q: I am welding a part that requires joining 347 stainless to 309 stainless. I am considering using E309L filler metal. What do you think?

A: There are a lot of possibilities for joining E347 to E309, but the best choice depends upon your intended use. If the joint is for high temperature service, which seems most likely, then ER347 would be the best filler metal. E309L filler metal would be an under-match for creep resistance at high temperature.

If the joint service is corrosion resistance at moderate temperatures, then you could use any of E308L, E309L, E316L or E347, whichever is readily available.

This column is sponsored by Penton and the Lincoln Electric Co., Cleveland. Dave Barton is a senior welding engineer in the Application Engineering Group of The Lincoln Electric Co. He oversees welding procedure development for both new technology and existing products, performs failure analyses for customers, and serves as a consultant on welding application problems. Barton has been with Lincoln Electric for 21 year. Send your questions for Mr. Barton in care of WDF by e-mail to: askdav@penton.com