Tack weld in welder qualification test

Date 04-04-2008 13:47

You probably can use an arrangement of clamping devices to position and secure the pipes in preparation for the welder that will weld the test coupons. However, the tack welds do more than simply hold the coupons together, they also maintain the proper root opening (provided they are of the right size and number). I don't believe the clamps would be sufficient to maintain the proper root opening once the welder begins to weld.

Most projects that I have worked on, the welder fits, tacks, and welds the entire test coupon. I can not recollect a situation where the pipe was fitted and tacked by a different person.

As for the number and length of tack welds, I most often see the welders use four tack welds about 25 mm in length at the 12:00, 3:00, 6:00, and 9:00 O'Clock positions.

Best regards - Al

By whip

Date 05-26-2008 03:18

Be very careful about what kind of tacks you let a testing welder put in a pipe coupon . Usually when fitting up and tacking up a test coupon it is loose laying in a angle iron and some times a welder will put the tacks right where the straps will be taken from, and sometimes they will make them nearly as long as the strap so that when they tack the coupon in position the difficult part of the root is done. So make sure you limit the length of the tack's you allow and explain what you will and will not allow on the test before the welder begins their test. I like to let the welder put 1 tack in the coupon then put that tack dead on top then tack the coupon in the position that the test is to be taken in and tack it to the table for the rest of the tacks and test.

WHIP

By raptor34 (**)

Date 04-05-2008 03:50

there should be four tacks made by the welder who is testing at every quarter, but if he wants to do it with out tacking let him and send him down the road when he busts his test part of the test is also to see if the welder can line up two coupons and weld them together, as simple as it may seem I have seen many welders not even be able to do that and who wants a welder that cant do even very minor fitting? are you sure you are using B31.3? I recently worked on a line of the same nature and API 1104 was used

By alkhiat (*)

Date 04-05-2008 10:50

THANK U , As you said" four tacks made by the welder who is testing at every quarter" , I want to know where could I find that ( in which code?) , also refering to Piping handbook chapter C2 FIRE PROTECTIOM PIPING table c2.2 You can find the suitable standards for ur fire protection system if you dont use NFPA STANDARD

By mick dale Date 04-05-2008 14:19

point raised in original question - ASME B31/3 states root tacks must be made using a qualified welder/operator. i'm sure it doesnt mention tacks that are removed though?

By dbigkahunna (****)

Date 05-26-2008 04:44

Does not make any difference. Under B31.3, tack welds must be made by a qualified welder, even if they are removed. Only a qualified welder can weld under 31.3
As for the exact lenght of the tacks ???? it does not made any difference! Some like short tacks some like long ones. Some like fat ones and others skinny ones.
BABRT's

By Shane Feder (****)

Date 05-26-2008 05:35

dbigkahunna,
Sorry, have to disagree.
The length of tack is important, also the positioning of the tacks.
A lot of welders will set up a 6G or 5G coupon on the bench in the 2G position for tacking. This is probably the easiest position to do pipe root runs with any process because you are in the most comfortable position.The more welding (longer tacks) he can get away with in the 2G position then the less welding he has to do in the much more uncomfortable 5G or 6G.
The positioning can also be abused. I thought as an ex-welder I knew most of the tricks a welder can pull but one guy caught me a beauty.
Put in four tacks in the usual places on a 6" pipe but instead of the normal 0,3,6 & 9 he had the tacks at 1.30,4.30,7.30 & 10.30.Welded forehand right across the bottom and then right across the top. When it came to the backhand side (the hardest on a 6G) instead of 6 o'clock to 12 he should have had he had 7.30 to 10.30 which was 1/2 as much weld.
I made the mistake of not explaining all my requirements and things that I would allow, not allow prior to starting the test.
You learn something new every day,
Regards,
Shane

By dbigkahunna (****)

Date 05-26-2008 22:08 Edited 05-26-2008 22:11

That is more of a matter of personal preference. Code is silent on tack lengths and location. I always liked mine 12, 3, 6 and 9. I liked long tacks. However I have see excellent results with the tacks in the quarters asnd short tacks. A good welder can make the weld regardless of the tack length or location. And if you are fitting, then you should be more consistant on where the tacks are and their length. I have seen fitting and tacks where it looks like it was done with a machine for length and location.
A welder test is another matter. On my stump speech the tacks cannot exceed 2 inches in length, and must be positioned at 12/6, 3/9. THe angle is checked with a protractor and cannot be less than 45 degrees.
BABRT's

By Shane Feder (****)

Date 05-27-2008 00:52

dbigkahunna,
With all due respect I have to query your statements again.
Please believe me when I state it is about broadening my knowledge rather than just arguing for the sake of it.
I agree with your statement about the code not addressing the issue of tack length or position but surely 2" tacks are oversize.
On a 6" coupon (168 mm OD) you have a circumference of 527mm, if you allow 4 x 50 mm tacks you will have 200 mm of weld done in the 2G or 1G position and only 327 mm done in the actual 6G test position. Surely this is not a true reflection of a 6G test. (I only allow 1" max tacks)
With regard to the 45 degree angle the code allows +/- 5 degrees so the test piece can be anywhere from 40 to 50 degrees.
Regards,
Shane

By dbigkahunna (****)

Date 05-27-2008 23:55

I should be clear. On a SCH 80 8 inch, the small 1 inch tacks will work, but I have seen them fail. I do not tell the welder how small the tack can be. It just is cannot be longer than 2 inches. I do not change that for the 2 inch sch 80 pipe. If they put in a short tack on the 2 inch, the fit up for the second tack is easier. Most welders will put in a 3/4 to 1 inch tack on the 2 inch and a 1 -1 1/2 inch tack on the sch 80. I have found when a welder wants to get cute with the tacks it is because of inexperience. I have never seen a welder put in 2 inch tacks.

I just say do em how you like em, just dont exceed 2 inches. That puts it in the welders backyard. I dont measure tack length because to me it is irrelevant. I check angle, fit up and high/low.
And while you are right, if the welder takes the long tacks then there will not be a lot of weld in the position, remember, on SCH 80 8 inch you are only looking at 2 inches of weld total. And I get to pick where the coupons come out of the quarter!
Also while code allows 5 degrees, I do not like to tell welders plus or minus anything. If I put my promag on it and it is 43 degrees, i dont say a thing. But most of the time the darlin sets it a 25 or 30 degrees. And if the angle is at 39, isnt that close enough?

On a production weld if the fitter/tacker wants 3 inches on the bottom and 1/2 on the top, as long as the high low is ok and it does not cause a war between the fitter and the welder, welder up. And if the guy is fitting his own welds, If he cant weld what he fits, doent need either of them.
Again, this is just me.
Regards,
BABRT's