I should have also compared this same example using the 1.3DP basis:
Shop stress during test = 0.2/0.5 x 1.3 = 52%
Operating stress (corroded) = 0.2/0.3 = 67%
This is a very undesirable situation and thats why we always insist on new and cold testing.
Sorry metengr but I agree with codeeng. In our refinery we specify new and cold testing for all new construction. A rough example using the original 15 psig design:
Calculated thickness: 0.2"
Corrosion allowance: 0.2"
Since we can't get 0.4" thickness we round up to 0.5"
Test pressure =...