One sound and one cracked transverse section of the weld were cut out and prepared for examination. Measurements of both cross section showed the size and shape of the weld to be the same. Therefore, the dilution and chemical composition of the weld should have been similar. Spectrographic analysis of the cracked specimen showed that the composition of the weld was: 0.11%C, 0.020%S, 0.022%P, 0.25%Si, 0.56%Mn, 0.002%Nb.
The factors controlling solidification cracking are: weld metal composition, weld solidification pattern (which depends on the shape of the weld), and the strain on the solidifying weld. A parameter has been developed to calculate cracking susceptibility using the weld metal composition:
UCS (units of cracking susceptibility) = 230C + 190S + 75P + 45Nb - 12.3Si - 5.4Mn - 1.
The UCS of the submerged-arc welds in question was 24. Research at TWI has shown that UCS levels of less than 10 indicate a high resistance to cracking and levels above 30, a low resistance.