Step 3: Compare the calculated fillet weld leg size to the smallest practical size.

Regardless of the application, there is a practical limit to how small a fillet weld can reasonably be made.

D1.1 Table 5.8 provides specific minimum sizes. For work not controlled by D1.1, or other codes that might have similar limits, simple test welds can be made to determine practical lower limits on fillet weld sizes.

To illustrate, assume that the calculation of step 2 indicated that a 3/16 in. fillet weld leg size is sufficient to transfer the load. However, if the weld is to be applied to, say, ¾ in. material, a 3/16 in. fillet may be impractical.

Step 4: If the comparison made in step 3 indicates that the calculated weld size is practical to make, a continuous fillet weld should be used. If the comparison indicates the opposite, go to step 5.

Step 5: Determine if the weldment is subject to cyclic loading.

If so, determine the applied stress range in the base metal — not in the weld — and compare that to the allowable stress range for Category E. If the applied stress range is greater than the allowable range, compare the applied range to the allowable range for Category B.

If the weldment is not subject to fatigue, go to step 6.

The applied stress range may be low enough that a Category E detail is acceptable.

When the stress range is too high for intermittent fillet welds, sometimes the added fatigue capacity associated with continuous fillet welds is acceptable.

If the applied stress range is too high for the continuous fillet weld, then the stress range must be reduced.

Step 6: Consider the manufacturing implications of intermittent versus continuous fillet welds.

The manufacturing implications were discussed in Part I. To summarize: If the manufacturing department would prefer to make continuous welds, it is typically wise for the designer to yield on this point.

Step 7: If intermittent fillet welds are still a viable option, then determine the appropriate combination of fillet weld leg size, segment length and spacing.

The intermittent fillet weld leg size should be the minimum practical size.

The minimum length should be at least four times (4X) the leg size.

Finally, proper spacing of the segments must be calculated.

In conclusion, there are indeed times when intermittent fillets should be specified. Using the information presented in Part I and the checklist provided here will help to you to determine when they are the right choice.

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Omer W. Blodgett, Sc.D., P.E., senior design consultant with The Lincoln Electric Co., struck his first arc on his grandfather's welder at the age of ten. He is the author of Design of Welded Structures and Design of Weldments, and an internationally recognized expert in the field of weld design. In 1999, Blodgett was named one of the “Top 125 People of the Past 125 Years” by Engineering News Record. Blodgett may be reached at (216) 383-2225.