Desin Pressure on line list

[silkroute]

Hi All,

I have little confusion while making 'line list' for a project.

What should be design pressure of particular line which is attached to a vessel? 'A design pressure of vessel' or 'design pressure as per piping class'?

silkroute

 

[gerhardl]

A line should be specified after two main criteria:
a) have a pressure class suited to the maximum pressure the line could be exposed to under working conditions (with relief if excessive pressure could occur accidently)
b) be commercial available and best cost/lifetime choice.

The rest is then up to you: if the vessel have a very low pressure, it may be better to choice a higher, commercial normal pressure class. If the vessel have a high pressure class, but the processes only require lower pressures you could use lower pressures for the pipelines. In the latter case the effective pressure class of the whole system will be the lowest.

 

[silkroute]

gerhard,

what should be design pressure / design temperature , if I want to specify on manual valve / actuated valve / pressure-temp transmitter / pressure-temp gauge data sheet on the same line ? as per piping class or equipment design pressure-temp ????

silkroute.

 

[gerhardl]

Any chain is as weak as the weakest link! You disqualify the whole line if any component is weaker than the others: allowed temperature and pressure is equal to the lowest classed component.

 

[advsign22]

What is the pressure rating of the flanges? Hopefully nobody designs less than the flange ratings.

 

[europipe]

advsign,
I hope everybody designs the press/temp less then the flange rating,
although it is a strange remark of you. (acc. EN/ASME?)

 

[SeanB]

I have seen it done both ways. However, my experience has been that the design pressure as shown in the line list is maxiumum pressure that the line can actually see. For example, if the line is connected to a vessel that is protected by a PSV then the maximum pressure the line can see is the PSV set pressure. Thus the design pressure of the line is equal to the PSV set pressure. Another example....the piping downstream of a pump. We would calculate the maximum discharge pressure from the pump. The design pressure of the piping is then set as the pump maximum discharge pressure. The hydrotest pressure minimum is then shown in the line list as 1.5 times the specified design pressure. The maximum hydrotest pressure in the line list is specified as the flange limit.

 

[BENSMIL]

I generally go by the piping class as it is easier to specify and gives a conservative value, quickly.

regards,
Benoy