Fabrication Workmanship during Fit-Up 4

[Melas85]

Hi everyone,

During fit up, my welders will grind and smooth the bevel surfaces and adjacent base material.
After which, we will notify the Client for Inspection and the time taken for them to inspect may varies. Sometime 1 day, 2 days or even 3 days.
So we will use a masking tape to cover the surface as it predominantly expose to external environment.

However I was thinking is there a better way than this? Do you guys have any suggestions other than masking tape in order to minimize re-work ?

What are your thoughts? Do let me know.

 

[MikeHalloran]

I would suggest blue painters tape, which will not rot in place and become difficult to remove, and will not leave a contaminating residue behind. Masking tape does both of those things.


Separate, perhaps unrelated, issue:

Notifying the client and having them inspect the parts is a good idea, and perhaps should be done before the slag is removed. A long time ago, I contracted with a steel center to have some complex parts flame-cut, welded, and machined. We provided drawings of the assembled parts, and also of the flame-cut components, just to make the assemblies easier to understand. The steel center cut the blanks a little large in some places, to provide material for the machinists to remove.

The welder took it upon himself to spend a godawful amount of time grinding off 1/4" of machining stock to make the components agree with our blank drawings before he started welding. We didn't get the call until after he had completed all the welding, and the machinists had nothing to cut away to make the finished surfaces.

A litle better communication, among all parties, would have saved all a lot of headaches. I wish the AWS standards said something about picking up the phone before picking up the damn grinder...



Mike Halloran
Pembroke Pines, FL, USA

 

[Melas85]

Hi Mike,

I couldn't agree with you more. The masking tape we used leave residue and before Client come and inspect, the fitters will quickly grind them. As our environment in Batam,Indonesia here is quite humid, the joints will tend to rust quicker than normal.

I also do agree with you about communication. It should be one of AWS Essential Variable in Chapter:Fabrications.
Haha. Thanks for the advise.

 

[gtaw]

There is a product on the market (at least here in the US) sold under the trade name "Bloxide." Basically, it is aluminum paint that protects the ground surfaces for several days. The paint is applied as a light coating, versus several built up layers, that can be left in place when welded. It a higher level if quality is required, the paint can be removed easily with a hand wire brush.

Best regards - Al

 

[Melas85]

Hi Al,

Just a quick search in google brings me to product you mentioned above. Am i correct to say the joint can be now welded even without hand wire brush?

Perhaps for the next job, I can propose/introduce the primer product during our procedure qualification and speed up the work during fabrication stage.

Im located in Singapore (fabrication yard: Indonesia) and I have this strong feeling the product might be available here as well. I try to search for it tmr.

Anyway Thanks Al for the advise. Its a good idea and suggestion.

 

[gtaw]

The marketers say you can weld over the paint. We, as a rule, wire brush the surface to remove as much as practical. In the case of carbon steel and high strength low alloy steels the little aluminum that remains is pretty benign.

In my personal opinion, no paint is better than a lot of paint, but some paint can be tolerated except in cases where the base metal has a high carbon equivalency and delayed cracking is known to be problematic. The higher the strength, the less tolerance for any surface contamination. However, when welding those types of steels, i.e., P91 for example, the cleaning requirements would typically call for the bevels to be cleaned with a solvent and ground to bright metal.

Best regards - Al

 

[Melas85]

Sure agree with the statement "no paint is better than a lot of paint".

Thanks Al for the advise.

 

[DekDee]

Melas,
There are quite a few weldable primers on the market but need to be careful.
Our contractor on the job I am on in Malaysia wanted to use some so I said they could use if they could prove the quality wasn't affected.
We did some fillet tests using FCAW and the welds looked great on the surface but when we fractured the welds the internals were like an aero bar - not good at all,
Cheers,
DD

 

[Melas85]

DD,

Do share the brand/maker of the weldable primer you just mentioned.

 

[DekDee]

Melas,
Interplate 317 by International Paints.
This product may actually be perfectly acceptable for some applications but it didn't seem to work for us.
Note: I have just checked the datasheet and it states excessive DFT may lead to increased porosity in the weld, maybe our contractor had applied it too thick.
We didn't wire brush it off as Al has suggested due to the fact we had a lot of areas where we couldn't get access and we needed to know if it would burn off during welding.
If you do try it please let us know how it went,
Cheers,
DD

 

[DekDee]

Google Interplate Zero as well Melas - just spotted it after I had posted,
Cheers,
DD

 

[Melas85]

DD,

I see. Thanks for the information that you have just shared. I will certainly take note of it and advise you guys if I might qualify/test with primers in the future.

 

[weldstan]

Over 35 years ago we qualified welding procedures for -50F service (impacts) and included radiography in the testing when welding over bloxide for the Prudhoe Bay gas/oil processing facilities. Back then we actually applied it correctly. Unfortunately, today's application is often done improperly - 3 to 4 times the appropriate thickness. We also attempted to qualify welding over some of the zinc rich thin film primers without success.

 

[tbuelna]

Some welding specs like AWS D17.1 require the weld surfaces to be free of "protective finishes". Rather than going thru the time and expense of qualifying a weld procedure involving some form of surface coating, you might be better off working with your customer to make a QA inspector available at all times.

 

[moltenmetal]

The last thing I'd want as a temporary primer is an aluminum paint, and any paint is likely to result in SOME porosity in the resulting weld. We've used weld-through primers for structural steel applications but not for pipe. If you don't care about porosity, then fine- people do weld under water... Best practice is to clean all surfaces to bare metal with abrasive just prior to welding. What you do between initial prep and that last step is pretty much irrelevant. If your environment is so bad that flash rust is occurring on one side of the weld prep before you're finished your root pass, then I defer to the local knowledge!

 

[racookpe1978]

DON'T use or allow anybody else to duct tape over your future weld joints: The residue is extremely hard to remove successfully and will (literally) gum up the works as your welders try to get the two surface clean enough to get good fusion.

The painters tape is a marginal substitute, but it is only "less worse" .

 

[Melas85]

I do appreciate each and every one comments here. I do take note of cost and time into the equation when qualifying a procedure. Personally this is my 1st year in structural fabrication while the rest of my 3 years I'm more lean towards offshore pipeline.

Thanks for the last few comments. I mean this is open discussion. Some of us surely has a positive experience using the products while other may not. This is my objective to gain knowledge between the two different sides of opinion.

Thanks everyone.

 

[DekDee]

Melas,
Masking tape is no good as as soon as it gets really wet it leaks.

racookpe,
Agree totally about duct tape on surfaces to be welded - however, we use it all the time as it is put on over the single-vee preparation to prevent moisture entering the prep (it never comes in contact with the actual welding surface).

moltenmetal,
Cleaning with abrasive is good idea but once the two pipes are tacked together you cannot get inside - imperative there is no rust inside the pipe when using GTAW process for the root run.

Cheers,
DD

 

[gtaw]

Good point DekDee. I've been called in on several piping projects because of "problems with the root" while welding pipe. The welders did a fine job of cleaning the outside of the pipe, but they didn't clean the ID. In one case, the problem was porosity in the welds after the welds were ground flush and polished. The welds joined stainless steel tubes to the tube sheet. The contractor was pulling his hair out because of the rework. The welds were completed with an orbital welding machine, so the parameters varied very little between one weld the next. I had the welder swab the ID of several tubes after porosity was found in the weld. As expected, the swab pulled a considerable amount material (soot, etc.) from the welded tube. I told the welder that if the tube was cleaned properly and completely, there should be no soot in the tube after welding. A change in the precleaning, expanding it to include the first four inches of the ID cleared up the problem.

Sorry for the hijack.

Best regards - Al

 

[gtaw]

My experience with the "Bloxide" was that it was easily removed with a wire brush just prior to welding. The paint is not intended for long term exposure to the elements. A light coating works very nicely, a heavy layer becomes a problem when it is time to wire brush it. It is not intended to be used on every metal, but it works effectively on carbon steel alloys as well as many high strength low alloy steels used in steel construction. I have used it for steel pipe coupons used to qualify welders. There was no evidence of porosity in coupons subjected to guided bend testing or radiography. When coupons were rejected, it wasn't due to porosity, but other causes such as undercut, incomplete fusion between weld beads, etc.

Any time I use a new product or one that I am unfamiliar with, I try it and test it to see whether it will work with my application.

Any product can be misapplied or misused. Often time people figure if a "little of this is good, a lot will be better." That isn't usually the case, but we must never forget the human factor. We can cure ignorance, but there is no cure for stupidity. Part of management's responsibility is to ensure the workers have the right information and use products as instructed. The ignorance factor is removed. If the worker refuses to follow instructions, it is time to remove the stupid factor by eliminating that worker.



Best regards - Al