Dear all,

Could you help me.
tr from internal pressure = 7.8 mm
tr from external pressure = 28.2 mm

from which tr, to determine MDMT ratio = (tr*E)/(tn-ca)

Thanks before.

Regards,
Tex

PS:
Codecalc result show that it take tr from internal pressure, why?

Tex,
If you are following the ASME Code to the letter then it appears that the tr should be the largest tr calculated. This would be based upon the external pressure calculation and not the internal pressure MDMT. From a practical perspective Part UCS was developed based upon tensile membrane stress and the potential for brittle fracture (the main purpose of MDMT) is increased with increased tensile membrane stress.

Since UG-116 does not define an MDMT at MAEWP then it may not be required.

EJL

I am not a "Vessel Man", but it should surely be more economical to ADD stiffening rings to reduce the thickness required for external pressure as long as your design temp. is not excessive (say <= 800 F, thermal gradient stresses typically reasonable).

OK, thanks.

I will use tr of shell from internal pressure at MDMT since external pressure don't produce general primary membrane tensile stress. (I guess )