ASME Code Standards for Pressure Vessels and Piping Engineering Practice Test

The key idea is that hydrostatic testing in this code section uses a safety margin above the actual operating design pressure. The required test pressure is 1.3 times the MAWP, and if the MAWP has been adjusted (for example, due to corrosion allowance or other design changes), that adjusted MAWP is the value you use. So the test pressure becomes 1.3 times the MAWP Adjusted. This ensures the vessel is tested well above the pressure it is permitted to operate under, even after any reductions reflected by the adjustment.

Using the unadjusted MAWP would ignore those reductions, and using a plain 1.3 × MAWP without accounting for adjustment could misstate the actual test level. The 1.3 multiplier is the standard factor, but it is applied to the MAWP as it stands after any necessary adjustments.