Pressure Vessel (Pressure & Temperature)

PRESSURE

 

A. Operating Pressure (OP)

Pressure at the top of the vessel during normal operation.

 

 

B. Maximum Operating

Hightest operating pressure foreseen for all applicable cases (normal, turndown, startup shutdown)

 

 

C. Desgin Pressure (DP)

The pressure to be considered when determining the thickness of the pressure vessel.

Maximum operating pressure plus a safety margin.

 

Maximum Operating Pressure, psig	Design Pressure, psig
Less than 25	50
25 to 250	Oper P + 25
250 to 1000	Oper P X 1.1
More than 1000	Oper P X 1.05 (*)

(*) Applicable only if pilot operated relief valves are used, otherwise use a 10 percent margin.

 

 

D. Maximum Allowable Working Pressure (MAWP)

Maximum pressure allowed at the top of the vessel during normal operation

 

 

E. Vacuum Condition (External Pressure)

- Equipment that operates under vacuum (including start up and shut down)

- Equipment is subject to vacuum during drainage

- Where loss of reboiler or other heat to a gas with a resultant cooling, even consensation, can result in a vacuum.

 

 

F. Effect of Pressure Drop on Mechanical Design

- Design pressure is at the top of the vessel in its operating position

- Mechanical design conditions at the bottom should consider"

  a. Liquid head

  b. Upflow or downflow pressure drop

  c. Hydrostatic test condition

 

 

 

 

TEMPERATURE

 

A. Operating Temperature (OP)

Temperature of Pressure Vessel during operation. (Including start and end of run)

 

 

B. Design Temperauter (DP)

The temperature to be determined whent designing pressure (Highest/ Lowest)

Normal operating temperature plus a margin.

 

- Maximum : Mean metal temperature based on highest expected operating conditions.

- Minimum : Mean metal temperature considering lowest operating, operational upsets, auto-refrigeration, atmospheric temperature, and many other sources of cooling.

(If operation is cryogenic (cold), the margin is a minus value (usually -25˚F), Alternative margins may be considered where the metallurgy is affected.

 

Normal Operating Temperature ˚F	Design Temperature ˚F
Less than 200	250 (*)
More than 200	Operating Temperature + 50

(*) 150˚F when caustic is present and the operating temperature is 100˚F, or less.

 

 

C. Minimum Design Metal Temperature (MDMT)

Standard temperature for impact test (Not considered for boilers operated at high temperature)