Steam PSV Pipe

[freakmeout]

What are the guidelines for sizing steam PSV pipe?

Should I take same approach as for sizing steam piping (since same median will flow through) or there are some other requirements?

Thank you.

 

[JohnGP]

You also need to consider the PSV, i.e. too much back pressure on the valve will affect its performance. It is usual to limit back pressure to 10% of the PSV set pressure (depends also on what type of PSV is to be installed).

Cheers,
John

 

[DLANDISSR]

FREAKMEOUT:
REFER TO ASME B31.1 APPENDIX II NONMANDATORY RULES FOR THE DESIGN OF SAFETY VALVE INSTALLATIONS

The size and length of the discharge pipe from a steam pressure safety valve is critical.
As the steam leaves the valve it expands. As it moves down the pipe it continues to expand so the velocity increases.
If the velocity reaches Mach 1 the flow rate will be what is called "choked flow". If this flow rate is less than the capacity of the relief valve the require relief flow cannot be attained. The associated equipment could then over pressure and explode.

You must calculate the equivalent length of pipe at which the velocity reaches mach 1. The actual equivalent length of discharge pipe must be shorter than the length required to reach mach 1.


Regards,
D Landis

 

[freakmeout]

Thank you.