Understanding API ICP653 Reading 7-Worksheet-04 Part1

9.3.3 Lapped patch plates may be used for thinning shells, below retirement
thickness.
9.3.3.1 Full fillet weld required on lap patch plates.
9.3.4 Lapped patch repair plates may be used to repair small shell leaks or
minimize the potential from leaks.
9.3.4.4 This repair method shall not be used if exposure of the fillet welds to
the product will produce crevice corrosion or if a corrosion cell between the
shell plate and repair plate is likely to occur.
9.3.4.5 This repair method shall not be used to repair shell leaks if the
presence of product between the shell plate and repair plate will prevent gas
freeing from the tank to perform hot work.
Charlie Chong/ Fion Zhang