8 replies to this topic

[Bhupat]

Sir,

I have system of "Fuel Oil Closed drain drum" located in ventilated pit below grade level, which is having PSV located and vented to atmosphere.

The PSV sizing is considered for the following cases:

1. Fire Case

2. N2 Blenketing Pressure control valve failure

3. Heating LP steam coil leakeg.

 

i want to understand how to calculaate the relief rate for case-3 steam coil leakege.

 

Can anyone advise me on this...consider me as new to this subject. I have limited knowlwdge on PSV sizing.

 

Any reference document would be of great help.

 

Thanks

Bhup

 

[fallah]

 

I have system of "Fuel Oil Closed drain drum" located in ventilated pit below grade level, which is having PSV located and vented to atmosphere.

The PSV sizing is considered for the following cases:

1. Fire Case

2. N2 Blenketing Pressure control valve failure

3. Heating LP steam coil leakeg.

 

i want to understand how to calculaate the relief rate for case-3 steam coil leakege.

 

 

Bhup,

 

How much leakage would be out of the coil?

 

If there would be reliable indicative facility for coil leakage no need to estimate the relief load due to leakage because mostly couldn't be the case for PSV sizing with respect to two other cases, if there wouldn't be such facility then you can suppose the leakage will lead to coil rupture for which you can take the maximum steam flowrate passing through the coil as PSV relief load in this case...

[Bhupat]

 

 

I have system of "Fuel Oil Closed drain drum" located in ventilated pit below grade level, which is having PSV located and vented to atmosphere.

The PSV sizing is considered for the following cases:

1. Fire Case

2. N2 Blenketing Pressure control valve failure

3. Heating LP steam coil leakeg.

 

i want to understand how to calculaate the relief rate for case-3 steam coil leakege.

 

 

Bhup,

 

How much leakage would be out of the coil?

 

If there would be reliable indicative facility for coil leakage no need to estimate the relief load due to leakage because mostly couldn't be the case for PSV sizing with respect to two other cases, if there wouldn't be such facility then you can suppose the leakage will lead to coil rupture for which you can take the maximum steam flowrate passing through the coil as PSV relief load in this case...

 

Falah,

Thank for your prompt responce. But, in our project client has ask to submit the calculation for the case of steam coil leakage in drum.

 

I am not aware of how to estimate the leakage out of coil? Is there any way to calculate?

 

This is just to understand for my knowledge Can i apply "Leakage of Two orific size" for this specific case as per API 5.19.3 method? if not

 

Then, As you said maximum flowrate though steam coil would be the conservative approach.

 

-Bhup

[fallah]

Bhup,

 

My comments are in red color as follows:

 

 

 

I am not aware of how to estimate the leakage out of coil? Is there any way to calculate?

The leakage intensity can be within a spectrum from a pinhole leakage to complete coil rupture. Then it's hard to estimate, other than you suppose the worst case i.e. complete coil rupture...

This is just to understand for my knowledge Can i apply "Leakage of Two orific size" for this specific case as per API 5.19.3 method? if not

Why not, you can apply such conservative approch...

Then, As you said maximum flowrate though steam coil would be the conservative approach. 

Using "two orifices method" can be more conservative than using maximum passing flowrate because might produce a larger relief flowrate...

[kinetic123]

Bhupat,

 

I believe standard method for gas orifice calculation could also be used for calculation of LP steam release from either a pin hole or complete rupture.

 

Fallah's comment/guidance would be more useful here?

[aroon]

Bhupat,

 

What is the coil size? Is it made from process piping with size above 1.5"?

What if the MOC of the Pit?

 

Fallah,

 

If coil is made from process piping with size above 1.5", still tube leakage/rupture scenario applies?

Also about fire scenario applicability, Bhupat has mentioned that it is below the grade level (but not sure it is underground or not). If it is under ground fire scenario doesn't apply.

 

Also, as per Bhupat post#3, if Client is asking steam leakage rate then should't it be from 6 mm pin hole as generally followed?

[fallah]

aroon,

 

My brief answers to your questions are in red color as follows:

 

 

 

If coil is made from process piping with size above 1.5", still tube leakage/rupture scenario applies?

It depends on design pressures of such coil and that of the drum itself.

Also about fire scenario applicability, Bhupat has mentioned that it is below the grade level (but not sure it is underground or not). If it is under ground fire scenario doesn't apply.

The drum is inside a ventilated pit without being buried, then the fire case cannot be ignored for it.

Also, as per Bhupat post#3, if Client is asking steam leakage rate then should't it be from 6 mm pin hole as generally followed?

Why not, of course if client approval for such assumption had already been gotten.

 

 

Edited by fallah, 24 April 2014 - 11:11 AM.

[aroon]

 

 

If coil is made from process piping with size above 1.5", still tube leakage/rupture scenario applies?

It depends on design pressures of such coil and that of the drum itself.

Thanks Fallah for clarifications. The point related to applicability of tube rupture for process piping is based on API-521-5.19.6. It state that "Units that use schedule pipe for the inner conduit or tube are no  more  likely  to  rupture  the  inner  pipe  than  any  other  pipe  in  the  system.  Therefore,  it  is  not  necessary  to consider a complete tube rupture as requiring a provision for pressure relief." I myself written off many scenarios based on this fact. Please correct me if I am wrong.

 

Edited by aroon, 24 April 2014 - 07:42 PM.

[fallah]

aroon,

 

API statement generally refers to the inner pipes not to be necessarily applied for heat transfer application due to higher thickness and poor heat transfer rate. Obviously, inner process pipes covered by mentioned statement aren't subject to complete rupture and as API states there is no need to consider a provision for pressure relief of any overpressure inside the relevant surrounding shell (drum or vessel) due to inner pipe complete rupture...