Eng-Tips is the largest engineering community on the Internet

Intelligent Work Forums for Engineering Professionals

  • Congratulations waross on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!

Continuous welds or not 1

Status
Not open for further replies.

haggis

Mechanical
May 18, 2002
290
US
Hi all,

I have a question regarding welds. As an example, if I need or specify a 2" lg fillet weld, I have been in the habit of specifying (2) 1" welds spaced at say 1 1/2" crs.

My reasoning is that if a crack develops in the 2" weld, it will propogate and eventially fail. Whereas, in the event of a crack in one of the 1" welds, the other will hold and repairs can be done.

My question is, why would some PE's be adverse to this and reqeust continuous welds in the drawing mark ups before certifying.
 
Replies continue below

Recommended for you

The starts and stops of a weld are a typical location for discontinuities. By making two welds rather than one, one doubles their chances of having a discontinuity that could result in a failure.

One of the most common crack in a weld is a crater crack or shinkage crack at the end of the weld. In Structural Steel Fabrication I probally find 1500 crater cracks to any other type of welding crack on new construction. On existing structures crack when found where either crater or shrinkage cracks missed during fabrication or fatigue cracking.

The starts and stops are also a stress concentrators, look for fatigue cracking to start here.

At the starts and stops expect to find more martensite (Hard and brittle) during to rapid cooling.

 
Just to reinforce the last reply from Rich2001, BS5135 states (Appendix A) "the effective length of an open ended fillet weld should be taken as the overall length less twice the leg length, thereby discounting the stop start positions which are generally of reduced profile. In any case, the effective length should not be less than four times the leg length."

There are other statements about fillets terminating at the ends or sides of parts being reterned continously aroud the corners for a distance of not less than twice the leg length. This procedure being important for fillets on the tension side of parts carrying a bending load.

There are probably other similar statements in other structural welding codes.
 
A continuos weld is always the best route to go but sometimes a skip weld is required to minimize distortion in a fabrication. In a practical sense your logic has some merit if the stops and start are free of defects.
One thing to remember is that when someone mentions leg length they were talking the longest leg. I was just involved in philosophical dispute about this and I lost.
 
Status
Not open for further replies.

Part and Inventory Search

Sponsor

Back
Top