Calculation of hoop stress in ASME B31.8, due to internal pressure load, it is allowed by Barlow's formula, from stress definition at par. 805.2.3 and 841.1.1.
The question is: "t" symbol in the Barlow's formula include or not the corrosion (internal external corrosion, erosion and metal loss). That it is not completely clear.
Actually CAESAR II use for hoop stress calculation the commercial thickness, without any deduction of corrosion.
If the user impose in CAESAR II - ALL CASES CORRODED then all stress (SUS, OPE, OCC...) take in account the corrosion with conservative results.
My suggestion is to permit at USER to consider the corrosion only for Hoop stress calculation and for SUS stress check but only for component Sp due to pressure, then not corroded thk remain for Sb and Sx evaluation in SL calculation and also for SE evaluation.
There are many technical articles that suggest to use wall thickness, deducting only the corrosion but not the manufacturer’s tolerance(see for example Pipe and Pipeline calculation manual second ed - J. Phillip Ellenberger - ELSEVIER-2014) to evaluate SUS and OCC stress.
In any cases when corrosion value is relevant we over estimate the margin of stress to use for Sb+Sx for SUS check or SE stresses for EXP check respect allowable stress. Considering or not the corrosion for only pressure load stress produce relevant difference in stress evaluation. Then what your opinion about this matter?