Continuous Welds

Structural Engineering general discussion Welding, Bonding & Fasteners
#1

QUESTION
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 propagate and eventually 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 request continuous welds in the drawing mark ups before certifying.

REPLIES

Rich2001
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 shrinkage crack at the end of the weld. In Structural Steel Fabrication I probably 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.

SOURCE
https://www.eng-tips.com/viewthread.cfm?qid=81750
Above is a snippet.

#2

I always though that the minimum weld length was 1.5”…

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#3

If the governing document cites AWS D1.1, the minimum weld length is four times the weld size, or the maximum weld size is the weld length divided by four. The 1 1/2-inch length is applicable to intermittent fillet welds.

I concur that the weld starts and stops account for many welding discontinuities. But there is a minimum weld size requirement that is a function of the base metal thickness. The minimum size is to ensure slow cooling provided the proper preheat is used and is dependent on whether a low hydrogen welding process is used or not. Slow cooling is intended to mitigate the probability of developing an undesirable microstructure in the HAZ. Where the load is minor and would result in a weld smaller than the minimum size based on base metal thickness, the intermittent fillet weld is the work around.

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