dualphase,
microhardness of the autogeneous seam
weld (Fig. 16). Vickers 50 g microhardness testing
differentiated between the two phases in the
weld fusion zone; the ferrite phase was 175
HV50 (88 HRB), and the martensite phase was
251 HV50 (23 HRC). The tube base metal hardness
met the 90 HRB maximum requirement of
ASME SA-268. Hardness testing required by
this standard is performed away from the weld
seam, in accordance with SA-450, paragraph
21.7 (Ref 31). Table 9 lists hardness values for
the tube-to-header welds.
A corroded tube-to-header weld sample
removed from the leaking header after seven
months of service was also hardness tested. Its
weld and HAZs, particularly the tube HAZ,