A diver inspection has detected a through$-$thickness circumferential crack, $70$mm long, in

the leg of an offshore production platform operating in the UK sector of the North Sea. The

crack is situated at the toe of a full penetration transverse girth weld, remote from the

bracing members but beneath the water line. The leg has a circular cylindrical geometry of

$4$m in diameter and a wall thickness of $25$mm$.$ Wave action causes fatigue loading

equivalent to $10$ cycles per minute at a constant amplitude axial stress in the range of

$15$N$/$mm$2$ at this location.

A previous defect assessment gave a maximum allowable length for a through$-$thickness

crack as $150$mm$.$ The fatigue crack growth is governed by the equation

da $31011($ K$)3\mathrm{.}5$

dN

$=$

where da $/$ dN is expressed in m$/$cycle and stress intensity factor range $$K

in MPa m $.$