Maximum Operating Pressure (MOP) - The maximum pressure at which a natural gas facility can be operated without further review, facility modifications, or documented operating procedures. This pressure can be limited by customer piping, downstream piping, operating agreements, etc.
Maximum Allowable Operating Pressure (MAOP) - Maximum established pressure at which a facility can be operated without documented operating procedures.
Maximum Inlet Operating Pressure – Maximum pressure the inlet piping can experience during normal operation.
Outlet Maximum Operating Pressure – Maximum pressure the outlet piping at a facility can be operated without further review, facility modifications, or documented operating procedures. This can be limited by customer piping, downstream piping, operating agreements, etc.
Outlet Maximum Allowable Operating Pressure – Maximum pressure at which the outlet piping can be operated without documented operating procedures.
Testing and adjusting relief and safety valves is important to safe system operation. This section discusses the various methods available to perform these tests safely and accurately.
Safety valves are normally tested both for relieving and closing pressure. This requires that the boiler pressure be raised until the valve opens and relieves sufficient pressure for the valve to close. Safety valve seats are susceptible to damage caused by wet steam or grit. Cleaning of the boiler and steam lines before testing safety valves is necessary.
Testing safety valves always requires special precaution. Safety valve exhaust piping and vent piping should not exert any excessive forces on the safety valve.
When a boiler inspector is carrying out an examination of a boiler, he must, by sealing the safety valve, ensure that the safety valve is so adjusted as to prevent the boiler from being operated at a pressure greater than the maximum permissible working pressure. The maximum permissible working pressure can be obtained from the certificate of fitness.
The seal attached to the safety valve should be maintained intact and the setting of the safety valve should not be altered by a person who is not a boiler inspector.
The set-point of the valve is the system pressure at which the valve begins to open.
The following general guidelines apply to set-point testing of relief valves, safety valves, and pilot valves:
Only qualified personnel are to conduct set-point tests.
Tests are normally conducted after a valve has undergone major repairs or overhaul.
Set-point tests are conducted through use of nitrogen, natural gas, or, for compressed air systems, air.
Bench testing and in-place testing are both used as applicable. For bench testing, the guidelines outlined above in Inspection Repair/ Removal are to be followed.
Personnel in the area in which a set-point test is to be conducted are to be notified.
Personnel involved in set-point testing are to use personal protective equipment and are to make proper selection and use of tools.
Personnel involved in set-point testing are to follow applicable depressurization/pressurization procedures and also follow lockout/tagout procedure where these procedures are applicable.
During set-point testing, the following environmental protocols are to be followed:
Contamination of soil, surface waters, and ground water is to be avoided.
Any waste materials that are generated are to be collected in approved containers and are to be disposed of properly.
Testing is to be documented through use of correct forms, with the forms completed properly.