Root pass, cap, etc

[johnpenn74]

Fellow Livesteamers,
Can some enlighten me as to why we do differing passes with differing weld rods on a full penetration weld on a boiler?
Ex we weld with 6010/6011 and then cap with 7018. I see numerous examples and reference in the threads about this technique.
Being the plate itself is 60,000 psi how does it benefit me to run beads with 70,0000 psi rods?
Is it unacceptable to take hotter 6014 and do all the welds with one class of rod?

JP

[Bill Shields]

most people building boilers in our hobby just do a 7018 and call it a day

[Marty_Knox]

Basically live steamers do it because that is the way code shops do it. In a properly prepared full penetration weld you start out with a gap at the base of the weld. You use 6010/6011 because it is a fill/freeze rod that will bridge the gap. You weld out with 7018 since it is low hydrogen rod, giving very low chance for porosity. Under ASME rules you write a weld procedure, weld samples to make sure you get the results you are looking for, then qualify your weldors on your procedure.

[Marty_Knox]

How do you know it is 60,000 plate? Most of the plate I buy these days is SA516-70, which is a 70,000 psi tensile strength.
Also, we do a lot of TIG root since we can use a closer fit. The other benefit to a TIG root is easier inter pass cleanup.

[redneckalbertan]

Different rods do different thing. The 6010/6011 is basically the same rod 6010 is a DC rod the 6011 is an AC rod . The difference between the 2 is the addition of something to stabilize and facilitate the retarding of the arc with the AC rod. These rods are very quick freezing, and deep pentetrating . If you are welding up a gap rod you don't want you puddle dropping out or drooping and forming grapes.

The 7018 is a low hydrogen rod that is suitable for dynamic loads. Hydrogen induced cracking is caused by moisture in the rod, that is one of the reasons why these rods are stored in a rod oven, according to code. 7018 is easy to weld with and gives the desired weld results.

7024 is not a deep pentetrating rod that has a lot of flux. The excess of flux can cause problems with slag inclusions in the weld if the welder is not careful in controlling the slag. It is not designated a low hydrogen rod and is more susceptible to hydrogen induced cracking, and if memory serves me it is not meant for dynamic loads.

6013 is not a good choice either. It is not a rod for dynamic loads and is not a low hydrogen rod.

[Russ Hanscom]

Some combinations have been proven to work, are relatively forgiving, and thus are most commonly used; however, if you want to do the testing and qualification procedures almost any combination can be used - just might not be practical.