5 replies to this topic

[JP2078]

I have ordered a diaphragm pump for injecting a chemical in the discharge line of the HP water pump. The discharge pressure of the pump is 165 barg where as its PSV is set at 181 barg. The HP water pump discharge pipe is designed for 140 barg and normal operating pressure at 124 barg.

Consider the normal operation that the chemical injection to HP water pipe is in progress, suddenly HP water pump tripped and discharge system gets isolated, the pressure inside HP water system will be at 125 barg while chemical injection is still on, and continued to push the chemical. As water is incompressible, with a fraction of minutes the biocide injection will generate a pressure of 140 barg (design pressure of existing system). 

There is no any protection on existing HP water system except design pressure (140 barg) of the system.

As this scenario will be occasional, shall I take credit for hydrotest pressure of 186.2 barg [As per ASME31.3, 302.2.4(f)]?  Also note that the existing HP water piping is already considered for excursion of 154 barg for surge scenario for 50 hrs per year.

               Hence can I still use the hydrotest pressure for this additional over pressure scenario?

[fallah]

JP2078,

 

If i well understood. the chemical injection pump can apply a permanent pressure around 181 barg i.e. the set pressure of relevant PSV, when HP water pump tripped and discharge system isolated. Then, why did you declare that the scenario is occasional?

 

Indeed, please upload a simplified sketch of the system and additional info to get more proper response...

[curious_cat]

In the setup, as described, isn't there the risk of the discharge piping being subject to a  182 barg or at least 165 bar under the trip scenario? 

 

Before this new chemical injection pump was installed how was the discharge piping of the HP Water Pump protected from overpressure?

[JP2078]

Hello Fallah

Thanks for reply

The pumps are water injection pump (centrifugal), and piping is designed for its shutoff head. These pumps are injecting water into multiple wells through choke valve. Hence the pump trip will lead to close choke valve manually, which may be rare scenario that whole piping network in getting isolated. Refer attached scheme. Also I have minimum recycle valve.

 

Shall I take advantage of  hydrotest pressure in this case for scenario described in first post ?

 

Hello curious_cat

It is water injection pump (centrifugal) hence line is designed for pump shutoff head that is 140 barg, it has got 2 oo 3 voted pressure trip to trip pump upon pressure surge in line. Recycle line is also provided which drain water back to sea.

 

 

 

Attached Files

•  Scheme.jpg   42.94KB   3 downloads

[fallah]

JP2078,

 

If the pressure variation is occasional and falls within the conditions described in clause (f) of B31.3 302.2.4, then it would be ok...

Edited by fallah, 15 April 2015 - 04:37 AM.

[JP2078]

Thanks fallah