Question regarding welds

[oengineer]

I have HSS 12x12x1/4 & HSS 8x8x1/4 members. I am welding a 3/8" gusset plate to both members using a 1/4" size continuous fillet weld. The 1/4" weld is strong enough for the load, but is it okay, construction and fabrication wise, to use the 1/4" fillet weld for the 1/4" thick members? The reason I ask is because the actual thickness of HSS 12x12x1/4 & HSS 8x8x1/4 members are 0.233". Will there be any problems using the weld size? Any suggestions/comments are appreciated.

 

[JedClampett]

I don't think that it's automatic for welds of the same size to burn through the base metal. It all depends on the welder. A good one won't have a problem.

 

[TLHS]

The maximum fillet weld sizes that people normally quote are for when you're welding along the thin edge of something.

You can generally build up a fillet weld as large as you need to if you need the strength. Large sizes can get uneconomical, because they take ridiculous numbers of passes compared to penetration welds, but they're generally feasible. Economics obviously aren't a problem if you're talking about a quarter inch weld.

Weld leg lengths that are thicker than the HSS wall are pretty typical. You need to do that if you want to develop the full strength of the tube in a truss, for instance. The table of minimum suggested weld leg sizes for trusses in the Welding For Design Engineers book put out by the Canadian Welding Bureau only shows fillet welds that have longer legs than the member wall size. The Canadian welding code also lists a leg size to develop full HSS strength, which is larger than the wall thickness.

Basically, make sure you have a load path out of the weld and have checked the base metal, but there's no reason you can't use a fillet weld that has a larger leg than the thickness of the materials you're attaching.

 

[racookpe1978]

On the other hand, you can specify a 1/4 fillet all the time - and you have.
You will never, ever GET a 1/4 fillet weld, because the actual wall thickness - of the steel you are purchasing (and apparently have measured!) - is only 0.233 thick.

SO, is 0.233 wall thickness adequate for your loads and your (previously assumed) safety factors? That is the important question.

 

[desertfox]

Hi

I wouldn't specify a fillet weld any bigger than the thickness of the smallest component to be welded, this link might help:-

http://www.twi-global.com/technical-knowledge/job-knowledge/design-part-2-091/

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[TLHS]

racookpe,

I'm not sure what you're saying. The leg thickness of a fillet weld isn't the throat thickness. A compatible weld material won't generally develop the full strength of a member if you pick a matching leg size on only one side of the plate.

desertfox,

"The maximum size of fillet weld is generally that of the thickness of the thinner of the two items being joined but very large fillet welds may cause unacceptable distortion and/or extremely high residual stresses."

The above quote from your source appears to be pulling requirements from the lap splice weld maximums where you're welding to the edge of a plate. This doesn't necessarily hold for other scenarios.

 

[canwesteng]

No issue - and you will get a 1/4" fillet weld, not a 0.233" like racoope suggests. Like TLHS said, this isn't uncommon.

 

[dhengr]

Oengineer:
Generally, you select over-matched (higher strength) weld metal w.r.t. the base metal. When you make a weld, you remelt some of the base metal into the weld metal, such that the weld is not quite as strong as the max. spec’ed. strength of the weld metal. Thus, you have the throat of the fillet, that is, (.707)(leg size), +/- any lack of penetration or added penetration due to the weld process; times an allowable weld stress slightly lower than the max. weld metal used, due to the mixing of the lesser base metal. Then, you also have the base metal, at a lower allowable stress level, right adjacent to the welded joint taking the same stress, and it has to pass the stress test.

For most welds, I will over-match the weld metal; that is, 70ksi welding rods and process for 50 or 60ksi base metal, and of course it is a low hydrogen process. Then, I design the welds to the base metal specs., that is 50 or 60ksi, so I don’t have to check the actual weld and the base metal adjacent to the joint on every weld. This seldom increases the size or length appreciable, once the welder is there doing the weld in the first place. Then, I well finesse the actual weld joint design or the base metal stress analysis, if needs-be in some instances.

 

[desertfox]

Hi TLHS

From the description given in the OP's post I cant tell whether he is making a lap joint or not, so I assumed that the gusset we be welded to each section based on edge thickness.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein