Wall Thickness Calculation is a document that aims to ensure that the selected wall thickness value meets international standard code rules by attaching the calculation results in the form of a table. Code type used must be in accordance with the type of service passed by piping line. On this occasion, Dad Engineer chose ASME B31.3 as the basis of reference formula to calculate Wall Thickness on pipe. In addition to ASME B31.3, there is also another reference which is ASME B31.8 which is used for service pipeline.
Here is the formula used in ASME B31.3 2010:
t = thickness value according to design pressure
P = internal design pressure value
D = Outside Diameter (OD) pipe according to standard table
S = Stress value material from table A-1
E = Quality factor of tables A-1A and A-1B
W = Factor reduction of welding strength according to para. 302.3.5(e)
Y = Coefficient value of table 304.1.1
Once known t value, then it is necessary to add corrosion allowance value to get Tm value (min. thickness required). From tm value, added again mill tolerance of 12.50% (+ mechanical allowance if required), then this is what we call actual min. Thickness, T.
Need to be explained in advance, the report above is compiled based on each piping line in the line list document in a project / plant and grouped by Piping Class. To be more detailed, there are several parameters that must be considered, namely:
- Piping Class ⇒ Piping Class / Piping Spec will determine the design pressure value used, example Piping Class / Spec “X” according to the table above
- NPS (Nominal Pipe Size) ⇒ In accordance with ASME standard B36.10M for Carbon Steel material, can be seen Outside Diameter (OD) based on NPS. OD values will always be the same regardless of schedule
- Design Code ⇒ Code that determines the type of formula to get wall thickness
- Sch (Schedule / Wall Thickness) ⇒ this Schedule value already exists from Piping Class according to NPS
- Material ⇒ Pipe Material according to Piping Class, as one of the parameters of value S and E
- Pipe Design Pressure (psig) ⇒ Pressure value that we take according to Piping Class / Spec, for example for class “X” above, the rating is 150 # with a temperature value of 100∘F, then the design pressure is 285 psig. Actually the pressure-temperature rating diagram of piping class/spec has been given by ASME code B16.5 which is classified based on material type.