Remelting of Tacks

Date 06-21-2007 15:42

Yours is a question I had to answer on my current project. comments from myself are between /*/ everything else is a direct quote.
ASME IX
QW-202.2 Groove and Fillet Welds
(a) Qualification for Groove Full Penetration Welds.
Groove-weld test coupons shall qualify the thickness
ranges of both base metal and deposited weld metal to be
used in production.

QW 200.2 /*last paragraph*/

"When more than one welding process or filler metal
is used to weld a test coupon, the approximate deposit
weld metal thickness of each welding process and filler
metal shall be recorded."
If it's not recorded, then it goes to essential variables
except as noted in QW-200.4

QW-200.4 Combination of Welding Procedures
(a) More than one procedure having different essential
or nonessential variables may be used in a single
production joint. Each procedure may include one or
a combination of processes, filler metals, or other
variables.

/*Middle of second paragraph QW200.4*/

"Alternatively, qualification for
root deposits only may be made in accordance with
QW-200.4(b). The deposited weld metal of each process
or procedure shall be included in the tension and bend
specimens, and in the notch-toughness specimen (when
required).

ASME II
SFA 5-4 UNS C CR NI MO
E308L-XX W30813 0.04 18.0-21.0 9.0-11.0 0.75
SDA 5-9
ER308L S30883 0.03 19.5-22.0 9.0-11.0 0.75

B31.3
328.5.1 General
(a) Welds, including addition of weld metal for alignment
[paras. 328.4.2(b)(4) and 328.4.3(c)(3)], shall be
made in accordance with a qualified procedure and by
qualified welders or welding operators.

(c) Tack welds at the root of the joint shall be made
with filler metal equivalent to that used in the root pass.

/*B31.3 alters the requirements of Section IX. in (c) refer to the carbon and chromium differences in deposited weld metal between SFA 5.4 and 5.9
It could be argued that the reduction in chromium and carbon contents falls within that statement. My current project has adopted that idea*/

API 620
6.9.1.1
The tack welds in butt joints to be welded manually
are removed before welding.

/*for manual welds in API 620 tacks are not allowed to remain.*/

D1.1
5.18.1 Temporary Welds. Temporary welds shall be
subject to the same WPS requirements as the final welds.

5.18.2.1 Incorporated Tack Welds. Tack welds
which are incorporated into the final weld shall be made
with electrodes meeting the requirements of the final
welds and shall be cleaned thoroughly. Multiple-pass
tack welds shall have cascaded ends.

/*D1.1 speaks for itself. The final weld is made with a qualified WPS and therefore the tack welds have to use the filler material that is qualified by the WPS used for the final weld.
In short, it has to be in the original WPS.*/

End quotes.

My opinion: It's not an absolute necessity to use the same process. It is however required to be qualified in all cases depending on the rules of the codes in question.
I think it's good industry practice to use the same process when possible.

I believe that is likely the root cause of your previous standard experience.

Regards,
Gerald

By tom cooper (**)

Date 06-21-2007 17:32

Hey Gerald - thanks for that thesis! I feel like you should send me a bill for the time you spent.

I did pick up on the B31.1 paragraph that you cited: "...Tack welds at the root of the joint shall be made
with filler metal equivalent to that used in the root pass..." and wondered why the Codes (except API which i don't deal with) don't specifically and explicitly state "TIG root shall require Tig tack" or SMAW root shall require SMAW tack". Since they use the "equivalent" word and didn't attempt to restrict the processes used, they must have intentionally left the door open. I then compared the chemistry of a 70S-* Tig rods one might typically use for tacking and 7018 SMAW fill electrode and although they are similar, they are different so does that make them not "equivalent". And so once again I'm faced with the practical question of does it matter? Probably only if I or someone else wants it to be and forces the issue.

Again, thankyou for your interest.

By CWI555

Date 06-21-2007 20:21

Well if you want a bill I can oblige you LOL. As said, I had already been down that goat trail for the contract I am currently on.

Regards,
Gerald

By tom cooper (**)

Date 06-22-2007 09:06

If you don't mind telling, what brought about the issue on your contract? and what was finally agreed to by all parties?

And before this subject gets away, have you ever had reason by any Code requirement to inspect tack welds by more than visual examination? I know I have been on jobs where inspection required PT on tacks but I cannot now find where it is mentioned in the Codes.

Thanks

By js55

Date 06-22-2007 17:03

Tom,
There is no prohibition in any code that I know of about mixing processes for tacks. There is no metallurgical (other than the ususal issues with Al and such welding over FCAW-S) or mechanical reason that I know of to create such a prohibition.

By CWI555

Date 06-22-2007 18:55

With all respect to js55, Please read again the the D1.1 code snippet. There are in facts rules for mixing processes. The operative word is qualified.
If the process is qualified, it's no problem, if it's not, then there is a concern.

In my instance, it was using stick to make tacks without having a qualified procedure for it. If you read ASME, mixing of processes are allowed, but you must have a qualified WPS to do so. I.E. same material/filler material 308L with 308L stick and tig. But again, both have to be qualified before they can be mixed. D1.1 will fall in line with the requirement to have the process qualified. If it's going to be incorporated into the weld, it has to be qualified.

As to the second part, I recall seeing that as well, but I also recall pt of the tacks being a site spec, not a code spec. and that was on mil spec work.

Regards,
Gerald