PSV in the 53B seal flush plan 2

[maintennance]

A 53B seal flush system is provided with a PSV . I have come across a TRV in the cooling water system. But what is the technical reason for having a PSV in the barrier side ?
Similarly for the 53B seal system , whether the accumulator and the cooler has to be designed for the process liquid side pressure ( MAWP of the Pump) and temperature? If so , if the process liquid temp is 200 Deg C, whether the bladder material to be suitably selected? Even if the seal leaks, the barrier fluid only has to go inside the Pump. In one of the document it has been designed for the process fluid temperature and the MAWP of the Pump. Thanks to clarify

 

[flexibox]

It is always recommended to have a PSV in these systems for overprotection. Some systems isolate the accumulator from the cooling loop and if this valve is accidently shut the pressure in the cooling loop will increase due to temperature and it will act as thermal relief. If you make up system is manual then it protects the system for over pressurization. I have experienced both problems and the thermal issue was a catastrophic failure when a PSV was positioned incorrectly.

Different companies have different design philosophies on the design Pressure/Temperature of the system. You have to make that call. Sometimes designing to MAWP is an overkill but you may have a HAZOP and come to a quick conclusion if discussed as a team.

You are right if the seals leaks barrier fluid leaks into the pump so you need to check your alarm settings and trip settings. Normally the barrier fluid will never see the process temperatures but some organizations assume worst case conditions; that is select bladder materials suitable for process temperatures. But what do they do when the process temperature is above 300C? Bladder materials is most commonly available in Nitrile, High Nitrile and Viton. Normally std nitrile material is used in most applications followed by high nitrile then Viton. The latter is most expensive.

Rule of thumb if you choose a welded pipe system with Flanged connections then design to MAWP for coolers and accumulators. If the system is compression fittings (these designs can handle very high pressures too) perhaps you can relax the specification a little.

trust that this helps

 

[maintennance]

Thank you very much for your answer.

 

[FloPac]

TRV on the coolwater side is quite common, in fact it is an absolute requirement if the in- and outlet of the CW are provided with a block valve. This is to prevent severe damage due to thermal expansion of the CW if the unit is operated and the coolwater would be trapped between the two (accidentally closed) valves.

A SRV on the barrier side is far less common and not very much wanted either. The SRV is a safety device, in theory only triggered due to a pump upset condition where the 53B is charged with the hazardous pump product. Subsequently the barrier liquid should be considered as hazardous liquid as well and should not be simply discharged into the atmosphere via the SRV; typically a 53B SRV discharge should be piped to a 'safe location', often not available, therefore not practicle nor wanted.

Regards,
Flopac(r)