7 replies to this topic

[shahidulislam48]

Hi,

I have a PSV to size according to API 520. Fire Case consideration.

 

Required relief capacity = 2086.67 kg/hr (fluid = water vapor)

Set P = 3.5 Barg

Relieving T = 153.6 deg C

 

I have found the sizing to be 3K4.

 

I have got quotation from Emerson (formerly Crosby) for same tag which is similar to my sizing 3K4.

On the other hand, I also have got quotation from LESER for same tag but the sizing refers to 2J3 valve.

 

Is it possible by using same API 520 sizing but having this huge deviation in valve size?

Please provide your valuable judgements.

 

Many Thanks

Shahidul Islam

Edited by shahidulislam48, 17 January 2018 - 12:18 AM.

[fallah]

Hi,

 

Without the adequate info in hand it's hard providing proper judgments about your query. The difference in PSV size might be attributed to the fire case if the PSV is sized just to handle the fire case. 

Second vendor has sized the PSV lower probably due to just pressure vessel code compliance as the PSV wouldn't no longer protect the relevant vessel in fire case and the vessel would mostly fail before PSV opening at the set pressure. 

Anyway, you can send the vendors calculation sheets to be evaluated, if you are interested to get much proper response.

Edited by fallah, 17 January 2018 - 02:45 AM.

[shahidulislam48]

Hi,

 

Without the adequate info in hand it's hard providing proper judgments about your query. The difference in PSV size might be attributed to the fire case if the PSV is sized just to handle the fire case. 

Second vendor has sized the PSV lower probably due to just pressure vessel code compliance as the PSV wouldn't no longer protect the relevant vessel in fire case and the vessel would mostly fail before PSV opening at the set pressure. 

Anyway, you can send the vendors calculation sheets to be evaluated, if you are interested to get much proper response.

Hi,

 

Please have a look on the uploaded data sheet and sizing sheet.

 New Microsoft Excel Worksheet.xlsx   14.24KB   78 downloads

 sizing sheet.pdf   95.67KB   74 downloads

 

Thanks.

[fallah]

Hi,

 

In your first post about the fluid state you mentioned it's "Water Vapor" while appears the LESER has used "API 520 sizing for liquid" according to his sizing sheet but getting reasonable density (2.745 kg/m3).

Hence the difference in sizing result may be due to using different coefficient of discharge by two vendors. Please recheck and inform...

Edited by fallah, 17 January 2018 - 05:19 AM.

[shahidulislam48]

Hi,

 

In your first post about the fluid state you mentioned it's "Water Vapor" while appears the LESER has used "API 520 sizing for liquid" according to his sizing sheet but getting reasonable density (2.745 kg/m3).

Hence the difference in sizing result may be due to using different coefficient of discharge by two vendors. Please recheck and inform...

Hi,

 

During fire case the relieving fluid's phase is vapor. That is also mentioned in the data sheet. The sizing is usually carried out by using vapor phase condition.

But I don't get how LESER could do such mistake by considering liquid phase despite having mentioned vapor phase on the data sheet.

 

But by considering liquid phase relief it is not possible to have a 2J3 valve.

 

Many thanks for you concern Sir Fallah.

 

It is better for me to consult with LESER regarding this issue.

[latexman]

The sizing (water vapor) is very near the edge between 2J3 and 3K4.  Using your numbers in my software shows Crosby can use a 2J3 too.  Sharpen the pencil and question every factor that is off even slightly!  What PSV/RD combination factor was used?  API uses 0.975.  What PSV flow coefficient was used?  What actual flow area was used?

[shahidulislam48]

The sizing (water vapor) is very near the edge between 2J3 and 3K4.  Using your numbers in my software shows Crosby can use a 2J3 too.  Sharpen the pencil and question every factor that is off even slightly!  What PSV/RD combination factor was used?  API uses 0.975.  What PSV flow coefficient was used?  What actual flow area was used?

What is PSV/RD combination factor was used?

-0.9.

What PSV flow coefficient was used?

-EMERSON, Kd=0.866 (derated) & LESER, Kd=0.801

What actual/ selected flow area was used?

-EMERSON=2.076 sq.in (ASME) & LESER=10.179 sq.cm (ASME)

 

Shahidul Islam

[latexman]

It's not really a "huge deviation".  It's the next size nozzle that is commercially available where the sizing is near the edge.  I would question the choice of combination factor, unless an inferior quality rupture disk is being used.  API suggests 0.975.  Then, a re-quote to a 2J3 will probably be forthcoming and you'll have an apples-to-apples comparison.