Over pressure protection for pressure vessels - ASME UG -125 standard

Pressure vessel protection standard UG-125:

All pressure vessels within the scope of this Division, irrespective of size or pressure, shall be provided with overpressure protection in accordance with the requirements of UG-125 or with overpressure protection by system design in accordance with the requirements of UG-140.


It is the responsibility of the user or his / her designated agent to identify all possible overpressure scenarios and the overpressure protection method used to mitigate each scenario

Ensure that the required overpressure protection system is properly installed prior to initial operation If a pressure relief device(s) is to be installed, the size and selection of the pressure relief device(s) on the basis of its planned service is the duty of the customer or his / her appointed officer. The purpose of the service shall include, but not necessarily, the following

•(-a) normal operating and upset conditions

•(-b) fluids

•(-c) fluid phases

The overpressure protection system need not be supplied by the vessel Manufacturer.

If a pressure relief unit is supplied, other than unfired steam boilers, it prevents pressure from increasing by more than 10% or 3 psi (20 kPa).

Overprotection protection by system design:

A pressure vessel does not require a pressure relief device if the pressure is self‐limiting and this pressure is less than or equal to the MAWP of the vessel at the coincident temperature and the following conditions are met:

User UG-140 is responsible for the choice to restrict the stress by system design In order to recognize and examine all prospective overpressure situations, the user will perform a thorough assessment. (MAWP cannot be exceeded by pressure)

If the pressure is not self-limiting, the system layout or the mixture of overpressure can protect a pressure vessel from overpressure.