We have a vessel designed to PD5500. It has hempisherical ends which are connected to the main cylinder in a fashion identical to the bottom picture on page 3/210 (page 268 in the pdf version) of PD5500:2009, i.e. the hemispherical end is thinner than the cylinder and with the median lines of both in line with each other, and the transition between them formed by a taper or "cone" section, with a butt weld end the thin end of the taper. My question is what minimum thickness applies throughout the taper section? Common sense tells me this should be the same as the minimum required for the hemispherical end, i.e. Eqn 3.5.1-3 on page 3/8 (page 66 in pdf), but is it as simple as this? Does the minimum thickness ramp up through the taper as it nears the cylinder? The reason I am asking this is there is pitting corrosion in this region and we are wanting to carry out a fitness for service assessment on the vessel which requires the minimum thickness as a starting point. If the pits do not go beyond the minimum thickness then the assessment does not have to be carried out as such.
On a related note we are going to do a thorough thickness scan of this area from the outside,I guess this will tell us the thickness perpendicular to the outside taper face, and not the actual cross sectional thickness if you were to cut a vertical plane through the taper, is this relevant and how would we deal with this?
On a related note we are going to do a thorough thickness scan of this area from the outside,I guess this will tell us the thickness perpendicular to the outside taper face, and not the actual cross sectional thickness if you were to cut a vertical plane through the taper, is this relevant and how would we deal with this?
