welding of piles w/o interpass cleaning

Date 05-08-2003 06:59

When welding the piles offshore one of the main criteria is the welding productivity. To decrease the time of welding(Horizontal position with 15 Deg bevel on lower tubular and 30 Degree Bevel on the upper tubular), upto 6.3mm electrodes are used effectively. Now, I have seen welders doing it in other positions and would like to know the nuances and precautions as well as the adv/disadv of using what some people call "slag welding". What it means is that for each layer, no cleaning of the slag is done in between runs . But by the welders' skill the slag is broken down and the turbulence of the weld metal and the arc force bring the slag back to the top(The slag cannot be remelted by the welding arc). Then after the completeion of each layer, the slag is wire brushed. What this would mean is that the cleaning time after every run can be avoided and cleaning time thus minimized. Anyone having any feedback/experience/comments please?

By CHGuilford (****)

Date 05-08-2003 13:18

I'd say that's a good way to put down a lot of weld metal quickly but it is not a good way to be sure the weld is sound and won't give troubles later. It sounds like the welders are being paid by the weight of electrodes consumed or on a piece work system.
Who is saying the slag breaks away because of arc action, the welders? If they don't chip slag away, they are likely to get slag entrapment. Further, how do they know they have proper fusion and sound weld metal underneath the slag? Turning up the amperage to "burn away the slag and impurities" is really just gambling. The only safe bet is when you personally load up the dice to give the numbers you want. Welding is the same, welders need to take steps to properly clean between weld passes, even grinding the profiles if needed to improve fusion and bead placement. Estimators and bosses need to look at the total welding picture, not just how many rods can be burned in an hour.
CHGuilford

By JTMcC

Date 05-08-2003 13:55

If I am reading your post properly, you are talking about running one pass, horizontally, then running aditional passes above until a complete row or layer of passes are complete and then wire brushing before starting the next layer? If so, then that can be done effectively by good welders, the layer of slag is very thin to nonexistant at the top of a horizontal bead, we have done this on pipe piles in the past. It is very similar to welding wide vertical up cover passes with several rods, and not cleaning until the entire vertical pass is complete.

JTMcC.

By sayeeprasad (*)

Date 05-12-2003 10:38

JTMcC
You got exactly what I was asking. Did you qualify procedures the same way too? Do you have any technical back up from consumable manufacturer(s) on this type of welding? What were the client response to this technique? Note that D1.1 has always required cleaning between each pass. This is noted in section 5.30.1 of the 96 - 02 revisions of the code. The code denotes "Before welding over previously deposited metal, all slag shall be removed and the weld and adjacent base metal shall be brushed clean. The requirement shall not only apply to successive layers but also also to successive beads..." any client objections that you were deviating from this clause?

By RonG

Date 05-12-2003 12:59

What is the difference in what you discribe and a verticle weave?

There sure is a lot of high pressure pipe welded with some pretty wide weave passes.

Have you ever noticed when you lay down a nice smoothe pass how the slag releases and drops off if you look at it real hard?

The heat and arc dig in below the tiny bit of slag (very thin) at the top of the pass.

By JTMcC

Date 05-12-2003 15:57

-I haven't personally qualified a procedure this way, and I don't know if anyone has, or if it is feasable to do so.
-I have no technical backup whatsoever. I do know that good welders can make UT and X Ray using this method.
-Yes it does appear to be illegal acording to D1.1.
-The client's were happy that we were progressing quickly!
- It seems more a matter of convienience rather than flat out speed, it doesn't really take long to wire brush a weld with a small or medium size grinder. It is inconvienient sometimes, especially when going in circles around a pipe pile, working from a plank, over water.

This really seems to be a technique applied in the field, probably in violation of code. But good and experienced welders can and do do it regularly. Sorry I can't be of more help. Keep us informed.

JTMcC.