ASME Code Rated PRV for Protection of Positive Displacement Pump

[Hydroxide01]

We are installing a new internal gear positive displacement pump for conveying slightly viscous, non hazardous liquids (100-500 cSt). Flow required will vary from 100-200 gpm, depending on demand, and will be modulated through a downstream control valve (a pump VFD to modulate flow will not work for this application). Due to the nature of a PD pump, if the process is only calling for 100 gpm, the PD pump will continue to build system pressure as it is designed to output 200 gpm.

We use a non ASME code, external pressure relief valve to limit pump discharge pressure that works quite well. I'm wondering if we need to be using a coded ASME valve in conjunction with this non code valve. B31.3 does not cover over pressure protection of pumps. B31.3 does say to reference Section VIII (pressure vessels) for selection of a pressure relief valve if one is required. However, in this case, I'm not worried about the piping over pressurizing. If an over pressure event were to occur somehow, the pump couplings and/or seal would fail before any pipe or piping component would fail.

Thoughts on this?

 

[NovaStark]

The PRV may form part of the pumping local circuit, so you'd most likely need to check the design code for the PD pump which may reference you to API 521 or similar. Then based on that it may be certified to ASME VIII or I or whatever code it specifies.

 

[RVAmeche]

Technically the PRV should be ASME Stamped. Paragraph 322.6.3 says all pressure relief devices required...shall be in accordance with BPV Section VIII, Division 1.

 

[JJPellin]

I would disagree with two points you make. Generally, a VFD is a better option to control the flow. If the pump puts out 200 gpm at full speed, it will put out about 100 gpm at half speed. And the energy consumption would be much lower at the lower speed. If the pump were blocked on the outlet, the piping could very easily fail before the motor overloads or the coupling fails.

Johnny Pellin

 

[EngrPaper]

Why not use a bypass to divert the remaining flow above the demand? Assuming of course, as you say, you cannot use a VFD. You could use a control valve on either the bypass or the flow demand to modulate. Similarly, you could use a diverting valve to control supply/bypass flow simultaneously.

 

[RVAmeche]

Since it's a PD pump you'd still want pressure relief regardless of the control scheme/VFD, unless it was maybe a SIL rated interlock and the PHA/hazop has determined it's adequate.

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