Fig. 3 — An arc strike a few inches to the side of a fillet weld. Fig. 4 — Arc strike coupon without grinding after bend Inspection Trends / Summer 2013 23 that is not intended to be fused into the weld metal. A small volume of base metal may melt momentarily when the arc is initiated. The molten metal may crack from quenching, or a small surface pore may form in the solidified metal. Microscopic examination of the surface and resulting microstructure typically reveals a martensitic structure with a carbon content that is usually higher than expected. These discontinuities may lead to extensive cracking in service. With respect to repair procedures, cracks or blemishes caused by arc strikes should be ground to a smooth contour and reinspected for soundness.” More information about arc strikes is found in Section C-5.29 of the Commentary for AWS D1.1, Structural Welding Code — Steel: “Arc strikes result in heating and very rapid cooling. When located outside the intended weld area, they may result in hardening or localized cracking, and may serve as potential sites for initiating fracture.” D1.1 Section 5.29 includes the following statement: “Arc strikes outside the area of permanent welds should be avoided on any base metal. Cracks or blemishes caused by arc strikes shall be ground to a smooth contour and checked to ensure soundness.” The message in these texts, especially when considered together, appears to be clear. Arc strikes are • Blemishes • Discontinuities • Changes to surface profiles • Not meant to be in the intended weld joint • Potential sites for initiating fracture • To be carefully avoided. Every arc strike needs to be taken as a serious condition and receive proper repair procedures followed by reinspection. This reinspection — the intent of which is to ensure soundness — is generally accomplished by magnetic particle testing (MT). Prior to the repair by grinding, and even after, porosity and/or cracks are often visible thus requiring further attention. What Arc Strikes Are Not To better understand arc strikes, let’s look at the converse to see what testing. Fig. 5 — Arc strike after grinding when run through a bend test. Fig. 6 — Notice the small cracks on left side of ground edge of arc strike.
Inspection Trends | Summer 2013
To see the actual publication please follow the link above