Is field welding really that expensive? 2

[Lion06]

I've always been taught that it is and to minimize field welding on the documents. What confuses me, however, is that if it's really that much extra cost to the erector why is so much unnecessary weld laid in the field?

I obviously only have a few years under my belt, but I've seen so muh extra field welding done that it makes me question the premise that it's cost prohibitive. On one recent project we had HSS shear connections thy consisted of a seat with a top angle. The top angle was for stability only so we called out for only the tips to be welded to the HSS. When on a site visit, however, they had everything welded up! The angle was welded all the way around ( to HSS and to the column) and the HSS
was welded all around directly to the column!

This happened in quite a few places. Why would they lay weld that is not called for if it's that expensive and coming out of their own pocket?

 

[Qshake]

I've always took this advice with a grain of salt.

In some geographical areas field welding is questionable and expensive due to a lack of experience in the trades. For example it's probably very common to see good quality welds laid in port area or areas where petro-chemical facilities are common. Many welders would AWS certified but probably certified in welds that the civil building industry just don't do. Since there is experience and an abundance of good welders price is probably good.

In areas where little field welding is ever done, the quality is poor and the price for good welders is high.

Aside from that, field welding is also differientiated by industry. Buildings and other structures with little fatigue concerns are welded on without too much concern. In bridges, there is virtually no field welding. This is due, again, largely to the poor quality and experience and difficult NDE testing that are required to be done in the field.

Mind you I'm not saying that field welding doesn't or shouldn't exist. Just pointing out that to get good experience, good welders and provide for apporpriate testing it's expensive.



Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[Ron]

Qshake is right. In the shop, welding is done "in position", meaning you can turn the piece to get the most expedient and easier weld deposition. It is also easier to test in the shop, because again, the pieces are accessible and easy to test in those positions.

In the field, the welding will often be done "out of position" meaning vertical and overhead welds will be necessary. These are the most difficult positions for welding, they take longer to put in properly and the failure rate of tested welds is much higher. Further, the testing is more difficult because of access, particularly if using radiographic testing on complete penetration welds.

So yes, field welding is more expensive for those reasons, among others.

 

[bootlegend]

I always assumed it was really the "set up" for field welding was the cost. There probably isn't much difference in calling out the tack welds or full welds, maybe 5 minutes versus ten minutes. But getting the manlift in place, getting the rods out of the truck, etc requires time where the shop is set up to be more efficient in that way.

And many times you'll have to touch-up paint after the field welds.

I don't know much about statistics, but I do know that if something has a 50-50 chance of going wrong, 9 times out of 10 it will.

 

[kelowna]

Time is money.

Field welding is much slower, has many more quality problems, requires more complex inspections and possible repairs, more qualified labour and involves more complex set up than bolted connections.

Having said that, sometimes you have to do what you have to do.

 

[Qshake]

Very succint Kelowna!

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[Lion06]

I agree. So the question is why would erectors provide so much more weld than called for on the drawings? I've seen this on several jobs in my short time.

 

[MikeHalloran]

A welder who was trained in/for the offshore oil industry will weld _everything_ 'all around' because it's required for corrosion control on offshore oil rigs.

Drawings I made for marine exhaust fabrication had few/no weld symbols because the default was 'weld everything'. I tried on a few occasions to get partial welds on particular special articles; couldn't be done.

There are probably other places where 'all around' is customary.





Mike Halloran
Pembroke Pines, FL, USA

 

[JStephen]

To answer your question, it was welded that way because somebody made a mistake. What exactly went on is a different matter. Maybe the guy welding didn't have a set of drawings to work from. Maybe they welded it the way the drawings said, and then thought, "Wow, that looks awfully skimpy, we'd better lay some more weld in there, whoever drew that probably made a mistake!" Maybe they are incorrectly applying lessons learned from a previous job. Maybe they misinterpreted the weld symbol(s). Anyway, they spent some money they didn't need to.

It was mentioned that in some applications, "all around" welding is common due to corrosion. If I recall correctly, the Structural Welding Code prohibits this in certain geometries, so per that particular code, more weld is not necessarily better.

 

[DRC1]

Field welding is more costly than shop welding. Much of the work in a shop can be automated, and for welds that are done by hand they can be rotated and held better, conditions are more controlled and inspection is easier. That said, not everything can be shop welded and some field welding is needed. Good details make a lot of difference.
In rsponse to your comment aout the HSS Tube connection, you should ask. It could have been a mistake. Or they may have increased the weld as they needed a guying point and did not think the weld would hold for that. Or they may have had problems with that type of connection in the past.Find out and let us know.

 

[BAretired]

I believe in minimizing field welding, not because it is more expensive, but because it is not as reliable as shop welding. Shop welding is done under more controlled conditions. I prefer to shop weld and field bolt because the probability of an understrength weld is substantially reduced.

In those cases where field welding is absolutely necessary, I have always insisted upon thorough welding inspection.

BA

 

[vthomidis]

I should aggree with BAretired.

In the field of preenginered steel buildings in which I am involved, field welding is very minimized.It is not easily reliable versus shop welding which is done indoor under controlled conditions.
Also in bridge construction ( as also already mentioned above ) is almost prohibited.

Of course in other works it can be of wider application provided that experienced and certified welders are easily available..

That as far as quality is concerned.

Besides,when a lot of welding work is to be done, the cost of field welding is clearly higher than shop welding.

 

[connectegr]

There are many factors related to welded/bolted steel construction.

I am presently working on a project that is nearly completely field welded. The fabricator that was selected does not have the equipment, CNC beam lines, etc. to accurately located and provided bolt holes. They selected and negotiated with the erector to field welded nearly everything. In this rare case things are proceeding smoothly. As connection designers we have tried to provide connection flexibility and field adjustment where ever possible. Structurally connection flexibility is a significant concern. For the erector, fit-up, column plumbness, and stability during erection can be a nightmare. In this case the project is a large commercial design with cantilever trusses and large axial loads. Many of the axial members required complete penetration welds of the flanges and/or webs. Due to welding considerations, preheating, weld shrinkage, etc. welding sequences had to be considered to maintain the structure geometry.

There are also additional costs related to the types of field welds chosen. There are additional cost for qualified welders. There is additional time and labor associated with with preheat, interpass temperatures, NDT testing, inspection, and repairs. These costs are also increased relative to similar shop procedures in a controlled environment.

Welding in general is more expensive than bolting, whether in the shop or field for most structural steel fabrication. With automated beam lines the fabricator can cut and drill all three surfaces of a wide-flange shape without physically touching the piece. The beam can be cut to length and drilled for connection angles and holes for filler beams. Most AISC certified fabricators will chose to shop bolt as much connection material as possible.

The most obvious exception to this are moment connections. Fabrication and mill tolerances can make flange bolted connections problematic in the field. And endplate moment connections can be limited by capacity. Erection stability is provided by field bolted web connections for shear. But there are exceptions, in some areas of the country qualified welders/iron workers are a premium and the fabricator may find field bolting an alternative.

With regard to providing more weld than required. This is primarily where fillet welds are required. Depending on the setup of the equipment, there is little additional time required for various sizes of single pass fillets. Welding in a vertical position, general deposits more weld metal depending on the welder's experience. In the field the welders prefer the largest diameter electrode allowed, where this may be useful in multipass welds, it is excessive when a 3/16 fillet is noted on the erection drawings. Remember welders know nothing about connection flexibility or ductility. Unless specifically instructed, they will weld till they run out of room. To the iron worker a little too much weld is better than having to come back to an area and overlay or continue a weld.

I can go on and on... Sorry

http://www.FerrellEngineering.com

 

[csd72]

I designed a few signs in New york and we used to use welding extensively for flexibility in alignment. No-one screamed about the cost.

I would say it really depends on how common it is in your area and section of the industry.

 

[PEinc]

In my experience, excessive field welding is very often a result of poor field supervision. If you ask a welder to weld something and then leave, he will still be welding the same joint when you return. Sometimes the welder hasn't even seen the welding requirement. He just keeps welding until the boss tells him to stop. I see more over welding than I do under welding.

http://www.PeirceEngineering.com

 

[Bobber1]

And keep in mind that AISC certified shops don't necessarily need full time weld inspectors, but field welding generally does require full time inspections.

 

[a2mfk]

connectegr should write an article, in all seriousness, many good points. Geography, fabricator and erector skills (maybe he has a welder that has some down time, and specifics of the jobs such as details, timelines, sequencing, weather, etc., all seem to play into this discussion. And there have been many well written articles in Modern Steel and other publications.

Frankly, its so hard to keep up with every economic consideration in steel detailing that I try to keep as many rules of thumbs as I can and then do what works and makes common sense. And good communication with your fabricator during the shop drawing process is extremely important.

OVERWELDING- keep in mind with some connections this is BAD. The one that jumps to mind is angle shear connections, bolted to the beam and welded to the supporting member. AISC places a limit on the return weld at the top of 2*weld thickness to retain flexibility, so that your simple shear connection can be modeled as a pin-pin.

Everyone else had great stories, many of which I have experienced. Having done specialty engineering for a steel fabricator for about 5 years now, we still get surprised. A couple of months ago they wanted to do all bolted connections, angles to girder webs, in the SHOP. Still not sure why, and they paid us to engineer it because it was not detailed that way by the EOR, and is not a standard AISC table either. Maybe a manpower and machine issue at the time they needed to go to production...

My one advice is on big projects with lots of steel connections, try if you can to get a steel fab on board before you do the connections, or give them as many options as economically feasible on your drawings (tables/schedules and typical details help), or defer them to the fabricator's specialty engineer.

And make friends with a good AISC certified steel fabricator. You can always pick up the phone for a second opinion and invite them to do the same. I have really enjoyed this experience...

HTH,
Andrew Kester, PE
Florida