5 replies to this topic

[farid.k]

Hye all.

 

Can I know what is the purpose of the bypass at the control valve as picture? I sure it is not for maintenance. Is it for start-up? If yes, how it will be use? Main pipe is 10”, the bypass size is ¾” with restriction orifice. No isolation valve at the inlet and outlet of control valve. This is for LP steam header.

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[fallah]

farid.k,

 

Appears it's for warm up of downstream line at start up conditions in which the control valve is initially closed and steam will be conducted toward downstream through the by pass line. When the downstream line temperature got increased to a prespecified value; the by pass line will be closed and the control valve will be permitted to operate...The RO is there to limit the steam flow during warm up operation...

Edited by fallah, 14 May 2015 - 10:32 AM.

[shan]

To pressurize the downstream piping system for satisfaction of the pressure differential limit of control valve. 

[farid.k]

thanks fallah and shan..
during normal operation, that line should be in close position?
how to determine the pipe size and orifice? what do they practise in plant is pipe 3/4" which is for me quite small.

farid.k,

Appears it's for warm up of downstream line at start up conditions in which the control valve is initially closed and steam will be conducted toward downstream through the by pass line. When the downstream line temperature got increased to a prespecified value; the by pass line will be closed and the control valve will be permitted to operate...The RO is there to limit the steam flow during warm up operation...

[fallah]

during normal operation, that line should be in close position?
how to determine the pipe size and orifice? what do they practise in plant is pipe 3/4" which is for me quite small.

 

 

farid.k,

 

Yes, during normal operation the by pass line is in closed position...

 

And yes, 3/4" line is small, but no need to be bigger besause the amount of steam would go through this line in advance of normal operation to warm up downstream will be considered as energy waste...

 

Sizes of the by pass line and relevant valves and RO are to be considered in relevant project spec as typical and depend on the main line size...
 

[shan]

You need to consider the downstream facilities (vessels and piping) volumes and time frame of pressurization to determine the flow rate, which reflects sizes of the bypass line and RO . RO is installed because the flow through 3/4" line, which is the smallest line based on the piping integration point of view, is still too large.