2 replies to this topic

[CPChem]

Dear Process Experts,

 

​I am reviewing waste heat steam generator system. The relief device ASME VIII on this system is designed for stream relief during blocked vapor outlet. However, there are control valve failure scenarios that leads to overfilling of steam generator. Fill time in this case is less than operator response time and upstream pressure is twice the design pressure. Credit of overhead steam line is not available as line designed for vapor service & possible hammering. Since, upstream pressure is twice the design pressure credit of basic instrumentation is not available and requires a SIL-3 instrumentation. Sizing PSV would not prevent BFW going to steam header. Hence, not trying to size the relief device for this cases. What are mitigations being followed in industry for such system.

 

Please advice.

 

 

[Pilesar]

SIL-3 is a tough standard to meet. Here are a couple of resources from internet search.

https://www.heatinga...ocess.com/sil3/

https://control.com/...3-system.45626/

It sounds to me like you need expert on-site help with this one.

[Halflight]

 Add pressure regulator valve front of control valve to make sure BFW would not come into the steam header with higher pressure than design pressure. It will prevent control valve failure case. And it's just based on your control valve doesn't make flash.