Welding Inspection & Metallurgy API ICP Self Study Notes

11.3 LACK OF FUSION WITH GMAW-S WELDING PROCESS
A large quantity of ASTM A 106, Grade B Pipe, 4 in. through 10 in. was found
to have lack of fusion (LOF) after being fabricated using the GMAW-S welding
process. This piping was in normal fluid service and required 5% radiographic
examination. Initially the radiographic film was read acceptable, but LOF it is
not easily interpreted by most radiographers.
During this piping project, a weld was found to have lack of fusion while
modifying a spool piece. The cut through the weld revealed the defect.
Follow-up investigation and further examination indicated the root pass was
acceptable in all cases, but subsequent weld passes exhibited LOF when a
radiographer experienced in this particular discontinuity, read the film. ASME
B31.3 considers LOF a defect.