Besides defective welds, the following named defects in welded pipes, with their causes, may be mentioned:

(1) Cracks or Seams. - These originate in the ingot as blow holes, shrinkage, cracks or other defects. An ingot defect lengthens out when the material is rolled into skelp.

(2) Blisters. - These are caused by piping in the ingot. Heat swells them above the surface of the skelp.

(3) Scale Pits and Sand Marks. - These are small indentations caused by rolling scale or sand into the surfaces of the skelp.