1 reply to this topic

[ankur2061]

Dear All,

I have a HP Steam separator connected to a HRSG. The function of the separator is to produce dry steam (>98%) from incoming wet steam (80%). The only inflow source to the HP separator is from the HRSG.
The separator is designed according to ASME Section VIII, Div. 2. The entire connecting system is desgined for the full rated design of the HRSG (source). I am attaching a sketch for clarity.

The upstream source i.e HRSG is protected by a relief valve set at 79.6 bar(g) with the downstream system (separator + wet steam piping + saturated steam piping + condensate piping) having a design pressure of 79.6 bar(g).

There is no source of hydrocarbons or any fuel near the entire system which can cause any external fire (jet or pool). Thus there is no external fire scenario.

In view of the above we have proposed not to provide any relief valve on the separator. However, the client has stated that vessels designed as per ASME Section VIII, Div. 2 have a mandatory requirement of a relief device.

After having a very careful look at the ASME code, I found that it is not mandatory to have a relief valve on a vessel designed as per this code as per clause 9.1.1 d) of the 2007 edition of the code. This is my interpretation what is written in the code. For the benefit of the readers I am reproducing a part the section 9.1.1 verbatim:

"9.1.1 a) All pressure vessels within the scope of this Division, irrespective of size or pressure, shall be provided with protection against overpressure in accordance with the requirement of this part.

9.1.1 d) The protective devices provided in acccordance with paragraph 9.1.1 a) need not be installed directly on a pressure vessel when the source of the pressure is external to the vessel and is under such positive control that the pressure in the vessel cannot exceed the MAWP at the operating temperature except as permitted in Section VIII, Div. 1. Note that pressure reducing valves and similar mechanical or electrical control instruments, except for pilot operated pressrelief valves, are not considered as sufficiently positive in action to prevent excess presures fom being developed."

I think I am fulfilling all the conditions as mandated by clause 9.1.1 d) for getting a waiver on installing a relief valve.

Friends, I need to know what you all think about this matter and whether in your opinion can I go ahead with the design of the separator without a relief valve.

Please refer the attached sketch for clarity of the system.

Anticipating your valuable comments.

Regards,
Ankur.

Attached Files

•  HRSG_Sketch.xls   18KB   75 downloads

[marthin_was]

I do agree with your opinion with few notes :
1. Downstream equipment (pressure vessel+piping) design pressure > or = design pressure HRSG (source)
2. If you look at API14C, your condition (with note (1) ), your case already fullfilling requirement not to install safety device

Dear All,

I have a HP Steam separator connected to a HRSG. The function of the separator is to produce dry steam (>98%) from incoming wet steam (80%). The only inflow source to the HP separator is from the HRSG.
The separator is designed according to ASME Section VIII, Div. 2. The entire connecting system is desgined for the full rated design of the HRSG (source). I am attaching a sketch for clarity.

The upstream source i.e HRSG is protected by a relief valve set at 79.6 bar(g) with the downstream system (separator + wet steam piping + saturated steam piping + condensate piping) having a design pressure of 79.6 bar(g).

There is no source of hydrocarbons or any fuel near the entire system which can cause any external fire (jet or pool). Thus there is no external fire scenario.

In view of the above we have proposed not to provide any relief valve on the separator. However, the client has stated that vessels designed as per ASME Section VIII, Div. 2 have a mandatory requirement of a relief device.

After having a very careful look at the ASME code, I found that it is not mandatory to have a relief valve on a vessel designed as per this code as per clause 9.1.1 d) of the 2007 edition of the code. This is my interpretation what is written in the code. For the benefit of the readers I am reproducing a part the section 9.1.1 verbatim:

"9.1.1 a) All pressure vessels within the scope of this Division, irrespective of size or pressure, shall be provided with protection against overpressure in accordance with the requirement of this part.

9.1.1 d) The protective devices provided in acccordance with paragraph 9.1.1 a) need not be installed directly on a pressure vessel when the source of the pressure is external to the vessel and is under such positive control that the pressure in the vessel cannot exceed the MAWP at the operating temperature except as permitted in Section VIII, Div. 1. Note that pressure reducing valves and similar mechanical or electrical control instruments, except for pilot operated pressrelief valves, are not considered as sufficiently positive in action to prevent excess presures fom being developed."

I think I am fulfilling all the conditions as mandated by clause 9.1.1 d) for getting a waiver on installing a relief valve.

Friends, I need to know what you all think about this matter and whether in your opinion can I go ahead with the design of the separator without a relief valve.

Please refer the attached sketch for clarity of the system.

Anticipating your valuable comments.

Regards,
Ankur.