I've used in the past 110mm of marine growth within of a depth of 0 to 30m. Density of 1400kg/m3 in air and 373kg/m3 in water.
This was project specific, reference from the DBM... but it appears to be inline with the Norsok referenc.
I have a concrete deadman reference using the following formula for area of steel:
As = M / 1.44 d
M = moment(ft-k)
d = section depth(inch)
Where the 1.44 comes from is not explained. Not being familiar with ultimate design, is this a common coefficient?
Thanks.