E6010 Root on 70ksi base material 2

[DoubleARon]

Excuse me if this has been discussed before, but my searching was unsuccessfull.

When welding a pressure vessel (assume 516-70 plate, ASME VIII Div 1), is it acceptable to use a weld procedure that was qualified with E6010 root, and E7018 fill and cap?

My dilemna is some companies want the 60ksi weld metal removed (backgouged) and back welded with 7018 to have the entire joint filled with 70ksi material. Their reasoning is that the calculations were completed using the stress values for the 516-70, so they cannot accept a joint with 6010 in it. However this seems flawed as the nozzles are likely SA106B (60ksi).

I have searched the codes and came up with the decision that it is ok to have a WPS using 6010 for a root, as long as the supporting PQR was qualified on 516-70 plate, and the tensile testing was acceptable (over 70ksi).

Any thoughts?

 

[metengr]

Procedure qualification and design basis for filler metal selection/use are two different topics. Yes, Section IX provides guidance for qualifying a welding procedure with a supporting PQR with your filler metal(s) of choice, but does not provide any guidance for filler metal selection.

Now, the question is can I use a lower strength filler metal for the root pass of a full penetration weld joint that assumes a tensile strength with a reduction factor?

For example, review ASME Section I, PW-15 and PW-15.2 Stress Values for Weld Metal, and for Section VIII, Div 1 UW-15. The strength of a weldment is based on the strength value of the base material x an appropriate strength reduction factor. From this standpoint, it is much easier to account for the entire weld made from ER70 and E70XX that matches the minimum strength requirement of the base material versus E60XX combined with E70XX. Otherwise, you need to account for the use of a lower strength filler metal in proportion to the minimum strength of the vessel material (see UG-41) in your design calcs.

 

[DoubleARon]

Neither of the Sect VIII paragraphs you mentioned talk about strength of filler metal, they talk only of a reduction of allowable stress based off the vessel material. Besides, the 6010 would not be used in fillet welds on any nozzle reinforcement, only on the full penetration welds of the nozzle to shell, which wouldn't matter as the nozzle will be 60ksi material.

Section IX already tells us to use a WPS / PQR capable of providing the required properties. So we do a coupon on 516-70 with 6010 / 7018, and the tensiles come out over 70ksi, which tells me you can use it on any 70ksi material.

My question is focused on full penetration shell welds, (long and circ seams).

Any other thoughts?

 

[metengr]

Ok. Having understood your question, ASME B&PV Code does not prohibit this practice for long seam girth and shell welds.

 

[deanc]

A thought:
Run a flat coupon. Cut,polish,and etch. If your root is full pen. single pass open groove 6010,think it will show that it has been consumed for the most part,at least to the bottom of the plate. So the result will be 70 ksi material for the thickness of the plate.

 

[DoubleARon]

No doubt, the tensile sample that is pulled could have next to no 6010 left. And any that was there would be diluted with the 70ksi base metal and 7018 anyways.

I was told this morning by our regulatory authority that the upcoming Sect IX and VIII editions are going to address this very issue, as it has been coming up. I think it falls into good engineering practice, you design a vessel with 70ksi material, you expect 70ksi filler material. The reality however is most fabrication shops use 6010 for laying roots as they would with piping. It is just something I was hoping to get a black and white interpretation for because sometimes these shops only understand that, but it doesn't appear to be going that way.

Something for people to be aware of at least. Thanks all.

 

[weldtek]

I agree with the comments above, but, if you write a generic WPS covering 60 & 70 ksi materials an issue may come up from your customer. You should be able to overcome any objections though, by limiting the application of the 60xx electrode to those P1 materials with a tensile strength < /= 60 ksi. You could write a WPS using 60xx and 70xx for the 106B / 516-70 and a separate WPS using just 70xx fillers for 516-70 /516-70 applications both supported by the same PQR.