API 682: maximum dynamic sealing pressure (MDSP) and maximum static sealing pressure (MSSP)

[CuriousMecEng]

Can anyone provide clarity in understanding:
maximum dynamic sealing pressure (MDSP) ( Barrier over Process)
maximum dynamic sealing pressure (MDSP) (Process over Barrier)
maximum static sealing pressure (MSSP)( Barrier over Process)
maximum static sealing pressure (MSSP)(Process over Barrier)

And its relationship with seal chamber pressure, pump and seal maximum allowable working pressure (MAWP), and maximum allowable working temperature (MAWT).

Thank you in advance.

 

[SB1976]

[pre]
Hi,

Please note -

MAWP : Maximum Allowable Working Pressure is the maximum pressure that a pump can withstand under static condition, when filled with water and water pressure increased. Essentially when hydrotest is carried out, water inside of the pump casing is pressurized at 150% of the claimed MAWP figures. From a purely design perspective (as followed by pump designers and manufacturers), this pump MAWP is determined from the same basic rules of thickness for pressurized vessels, i.e. pump casing thickness in combination with material of construction (yield strength / ductile limit etc.).
Also, as in pressure vessel design, MAWP is dependent on temperature. Higher the temperature lower the MAWP and vice versa. Hence, for a range of temperature, MAWP is maximum when temperature is minimum, and MAWP is minimum when temperature is maximum. Thus, as can be seen, MAWP cannot be stated in isolation. It has to be accompanied by corresponding temperature as well. This temperature is the MAWT.

MAWT : Maximum Allowable Working Temperature is the maximum temperature which the pump can withstand, and beyond which it will fail. MAWP corresponding to MAWT is the actual way of representing MAWP.
For example : As per API 610, OH2 type pumps shall have a minimum MAWP of 40 barg@38°C.

Sealing Pressure : Sealing Pressure or Seal Chamber Pressure is the actual pressure inside of the pump sealing area due to the fluid inside.

MSSP : Maximum Static Sealing Pressure is the maximum seal chamber pressure when in static condition.

MDSP : Maximum Dynamic Sealing Pressure is the maximum seal chamber pressure when in operating condition.

Should mechanical seals be designed same as pump MAWP? No, as per API 682, only under exceptional circumstances should seals be rated for MAWP. It is generally a Purchaser requirement.

In case of seal plan 52, barrier fluid (actually buffer fluid) pressure is less than leaked process fluid pressure. Hence the term "Process over Barrier". In case of seal plan 53, barrier fluid pressure is more than leaked process fluid pressure. Hence, it is called Barrier over Pressure".

Trust above helps.
[/pre]

 

[CuriousMecEng]

@S.Barman: Thank you for the reply.