"memoria de calculo" might translate exactly as calculation memory, but it's meaning is much more like
Calculation Report (or notes or log).
Given that you're designing to ASME B 31.4, you simply write a mechanical design report for this item following the calculations required in 31.4 for a pressurized piece of pipe.
so start with the data, Pressure, temp, size, design factor, type and grade of steel etc then calculate the wall thickness for the two barrels.
You might need to do a quick stress check as the trap will be supported on two legs so has some small bending moments.
Job done.
Or ask the vendor to produce one.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.