17 replies to this topic

[Ramesh-29]

Dear All,

 

As per the API, Tube Rupture scenario is not considered for Shell side of the exchanger if shell side design pressure is equal or higher than the 10/13 time of tube side design pressure (10/13 rule).

Could we apply the same rule for blocked outlet scenario? where the lower pressure vessel design pressure is higher than the 10/13 time of higher pressure side.

 

I want to know whether the rule is only applicable for shell and tube exchanger or applicable all places?

 

Thanks

Ramesh

[fallah]

 

As per the API, Tube Rupture scenario is not considered for Shell side of the exchanger if shell side design pressure is equal or higher than the 10/13 time of tube side design pressure (10/13 rule).

Could we apply the same rule for blocked outlet scenario? where the lower pressure vessel design pressure is higher than the 10/13 time of higher pressure side.

 

I want to know whether the rule is only applicable for shell and tube exchanger or applicable all places?

 

 

Ramesh,

 

Good point....!

 

At first be informed in new editions of API 521 the 10/13 rule is changed to corrected hydrotest pressure i.e. "Tube Rupture scenario is not considered for Shell side of the exchanger if shell side design pressure is equal to or higher than the corrected hydrotest pressure of tube side.

 

In my opinion, although there is no similar criteria in API 521 or other relevant standards clearly mentions this rule is applicable for blocked outlet case, it can be applied to this case too; i.e. where the lower pressure vessel design pressure is higher than the corrected hydrotest pressure of the higher pressure side.

[ankur2061]

Ramesh,

 

If the corrected hydrotest pressure for the shell side is lower than the design pressure of the tube side then a PSV would be required considering a tube rupture case for the shell-and-tube exchanger.

 

 

Corrected hydrotest pressure is defined as follows:

P_corrected = P_hydrotest x (σ_scenario / σ_hydrotest)

 

Where:

P_corrected = Corrected hydrotest pressure, kPag

P_hydrotest = Hydrotest pressure, kPag (Current ASME Code for pressure vessels defines as 1.3*MAWP)

σ_scenario= Material stress at the overpressure scenario temperature, MPa

σ_hydrotest = Material stress at the hydrotest temperature, MPa

​

​Hope this helps.

 

​Regards,

​Ankur.

[Ramesh-29]

 

 

As per the API, Tube Rupture scenario is not considered for Shell side of the exchanger if shell side design pressure is equal or higher than the 10/13 time of tube side design pressure (10/13 rule).

Could we apply the same rule for blocked outlet scenario? where the lower pressure vessel design pressure is higher than the 10/13 time of higher pressure side.

 

I want to know whether the rule is only applicable for shell and tube exchanger or applicable all places?

 

 

Ramesh,

 

Good point....!

 

At first be informed in new editions of API 521 the 10/13 rule is changed to corrected hydrotest pressure i.e. "Tube Rupture scenario is not considered for Shell side of the exchanger if shell side design pressure is equal to or higher than the corrected hydrotest pressure of tube side.

 

In my opinion, although there is no similar criteria in API 521 or other relevant standards clearly mentions this rule is applicable for blocked outlet case, it can be applied to this case too; i.e. where the lower pressure vessel design pressure is higher than the corrected hydrotest pressure of the higher pressure side.

 

Mr.Fallah,

Thank you for your response, I am little bit not clear on your statement, as per latest API 521, if shell side corrected hydro test pressure is equal or greater than the tube side design pressure then tube rupture case is not considered. Please correct me if I am wrong.

As per your reply, shell side design pressure should be equal or higher than the corrected hydro test pressure of tube side which may not be possible.

 

Regards,

Ramesh

[Ramesh-29]

Ramesh,

 

If the corrected hydrotest pressure for the shell side is lower than the design pressure of the tube side then a PSV would be required considering a tube rupture case for the shell-and-tube exchanger.

 

 

Corrected hydrotest pressure is defined as follows:

P_corrected = P_hydrotest x (σ_scenario / σ_hydrotest)

 

Where:

P_corrected = Corrected hydrotest pressure, kPag

P_hydrotest = Hydrotest pressure, kPag (Current ASME Code for pressure vessels defines as 1.3*MAWP)

σ_scenario= Material stress at the overpressure scenario temperature, MPa

σ_hydrotest = Material stress at the hydrotest temperature, MPa

​

​Hope this helps.

 

​Regards,

​Ankur.

 

 

Mr.Ankur,

 

Thank you for your response.

 

I am now clear about the rule to consider tube rupture PSV for shell and tube exchanger.

My query is the same rule can be applied to other places. For example, If Low Pressure Separator Hydro test pressure is greater than the High Pressure Separator design pressure then blocked outlet scenario will not be considered as credible scenario. Please share your view.

 

Regards,

R.Ramesh

 

[fallah]

 

 

Mr.Fallah,

Thank you for your response, I am little bit not clear on your statement, as per latest API 521, if shell side corrected hydro test pressure is equal or greater than the tube side design pressure then tube rupture case is not considered. Please correct me if I am wrong.

As per your reply, shell side design pressure should be equal or higher than the corrected hydro test pressure of tube side which may not be possible.

 

Regards,

Ramesh

 

Ramesh,

 

To be not confused; please note that in general the tube rupture case isn't applicable for a S&T exchanger if: "The corrected hydrotest pressure of the lower pressure side to be equal to or higher than the design pressure of the higher pressure side."

Edited by fallah, 26 April 2018 - 01:57 AM.

[Ramesh-29]

 

 

 

Mr.Fallah,

Thank you for your response, I am little bit not clear on your statement, as per latest API 521, if shell side corrected hydro test pressure is equal or greater than the tube side design pressure then tube rupture case is not considered. Please correct me if I am wrong.

As per your reply, shell side design pressure should be equal or higher than the corrected hydro test pressure of tube side which may not be possible.

 

Regards,

Ramesh

 

Ramesh,

 

To be not confused; please note that in general the tube rupture case isn't applicable for a S&T exchanger if: "The corrected hydrotest pressure of the lower pressure side to be equal to or higher than the design pressure of the higher pressure side."

 

Mr.Fallah,

So can we apply the same rule to other places? For example, If Low Pressure Separator corrected Hydro test pressure is greater than the High Pressure Separator design pressure then blocked outlet scenario will not be considered as credible scenario. Please share your view.

 

Thanks & Regards,

R.Ramesh

 

[fallah]

 

 

Mr.Fallah,

So can we apply the same rule to other places? For example, If Low Pressure Separator corrected Hydro test pressure is greater than the High Pressure Separator design pressure then blocked outlet scenario will not be considered as credible scenario. Please share your view.

 

Thanks & Regards,

R.Ramesh

 

 

Ramesh,

 

If you had read my first post precisely, you had seen i mentioned there: it can be applicable for blocked outlet case...

Edited by fallah, 26 April 2018 - 02:51 AM.

[Ramesh-29]

 

 

 

Mr.Fallah,

So can we apply the same rule to other places? For example, If Low Pressure Separator corrected Hydro test pressure is greater than the High Pressure Separator design pressure then blocked outlet scenario will not be considered as credible scenario. Please share your view.

 

Thanks & Regards,

R.Ramesh

 

 

Ramesh,

 

If you had read my first post precisely, you had seen i mentioned there: it can be applicable for blocked outlet case...

 

Mr.Fallah,

 

Thanks for your reply.

 

Regards,

R.Ramesh

[Technical Bard]

Explain how a blocked outlet case cares about the other side of the exchanger?    

 

If the maximum source pressure of the blocked outlet is higher than the design pressure of the exchanger side through which the fluid flows, then a PSV is needed for blocked discharge.  If the maximum source pressure of the fluid flowing into a pressure vessel is higher than the design pressure, then you need a PSV for the blocked discharge case. 

 

The only time the 10/13 rule applies is if the tubes FAIL in the exchanger.

[fallah]

Explain how a blocked outlet case cares about the other side of the exchanger?    

 

If the maximum source pressure of the blocked outlet is higher than the design pressure of the exchanger side through which the fluid flows, then a PSV is needed for blocked discharge.  If the maximum source pressure of the fluid flowing into a pressure vessel is higher than the design pressure, then you need a PSV for the blocked discharge case. 

 

The only time the 10/13 rule applies is if the tubes FAIL in the exchanger.

 

Appears the OP query hasn't been well understood...

 

In fact, OP wants to know if the criteria for applying a pressure relieving device on the exchanger's shell or tube side for tube rupture case due to different design pressure could also be applicable for two sequential pressure vessels with different design pressure but for blocked outlet case...?

[Bobby Strain]

 

Nowhere does the API practice mention 10/13. That's because there is no such definition. The text conveys the proper criteria.

 

Bobby

[Technical Bard]

 

Explain how a blocked outlet case cares about the other side of the exchanger?    

 

If the maximum source pressure of the blocked outlet is higher than the design pressure of the exchanger side through which the fluid flows, then a PSV is needed for blocked discharge.  If the maximum source pressure of the fluid flowing into a pressure vessel is higher than the design pressure, then you need a PSV for the blocked discharge case. 

 

The only time the 10/13 rule applies is if the tubes FAIL in the exchanger.

 

Appears the OP query hasn't been well understood...

 

In fact, OP wants to know if the criteria for applying a pressure relieving device on the exchanger's shell or tube side for tube rupture case due to different design pressure could also be applicable for two sequential pressure vessels with different design pressure but for blocked outlet case...?

 

 

That would most definitely NOT be allowed under ASME or PED

[fallah]

Technical Bard,

 

The matter is other than you are supposing to be...!

 

The OP are trying to know if the criteria for removing the over pressure scenario due to tube rupture in S&T heat exchangers among all other credible scenarios is also applicable for over pressure scenario due to blocked outlet in sequential pressure vessels with different design pressure.

 

Hence deletion of any required pressure relieving device isn't the matter of this thread at all and yes, even if there would be no credible over pressure scenario for a pressure vessel, it should be equipped with a pressure relieving device for code, say ASME, compliance...

[Technical Bard]

If you have two pressure vessels in series, and the second one has a lower MAWP than the first, it needs a PSV that can handle the flow that can happen between the two in the blocked discharge scenario, or in a control valve failure scenario (for a CV between the vessels).  While I have seen some companies try to claim that if the downstream vessel test pressure is above the upstream design you can ignore it, this is foolish.  Hydrotest is done cold and slowly.  Blocked discharge or CV failure will happen at operating temperatures and generally be very quick in how the increased pressure is applied.  Even if the downstream vessel survived such an event, it would have been seriously overpressured and most jurisdictions would not allow it to be placed back into service without significant re-inspection (including radiography, dye penetrant, ultrasonic) to ensure it was still in as-built condition.    The ASME code is clear that vessels must be protected against overpressure.

[fallah]

The hydrotest is done at ambient temperature but the corrected hydrotest pressure (Hydrostatic test pressure multiplied by the ratio of stress value at design temperature to the stress value at test temperature) should be considered for evaluation.

 

The attached phrase from API 521 included the credibility of relying on "corrected hydrotest pressure" as a matter based on which we can take credit on administrative controls to prevent overpressure in closed outlet scenario.

 

If your mentioned evaluation for blocked outlet case (...Even if the downstream vessel survived such as event, it would have been seriously overpressured and most jurisdications would not allow it to be placed back into service without significant re-inspection...) is being correct why the same scenario such as tube rupture case isn't covered and supervised by this evaluation at all in any relevant codes and standards?

 

Bottom line, is that as I mentioned in my first post: the criteria of removing overpressure scenario for low pressure side of an exchanger due to tube rupture CAN be applied for blocked outlet case and you might not find this criteria as clear as for tube rupture in relevant codes and standards.

Attached Files

•  Tube Rupture criteria for Blocked Outlet.pdf   55.04KB   201 downloads

[Technical Bard]

That phrase is advising the administrative controls should not be trusted alone if the corrected hydrotest pressure might be exceeded in an event.  I have yet to find a Client who would accept an administrative control in that scenario.  The recommendation clearly is towards a pressure relief valve set at the MAWP.  ASME does not have the allowance API appears to grant, and in many jurisdictions would not be allowed.

 

Heat exchangers that have a tube rupture event and were designed for 10/13ths (or the old 2/3rds) rule should ALWAYS be inspected before being placed back into service.  The Energy Institute (IP) did a Joint Industry Project in 2000 that flagged the problem of shock waves in exchangers than undergo tube rupture, with the advice that PSVs may not open fast enough (rupture discs are recommended, especially for smaller exchangers).  This was updated more recently (https://www.energyin...ar-may-2016.pdf) if your organization is an EI member.

[fallah]

 

Heat exchangers that have a tube rupture event and were designed for 10/13ths (or the old 2/3rds) rule should ALWAYS be inspected before being placed back into service.  

 

The above mentioned practice, if is to be followed by some engineering companies for S&T heat exchangers (or a pressure vessel) due to subjecting to a pressure equal to their corrected hydrotest pressure, doesn't cause having credibility of tube rupture scenario and still it can be removed from credible overpressure scenarios for mentioned exchangers.

 

As i mentioned several times ASME clearly mandates protection of all pressure vessels by pressure relieving devices against credible overpressure scenarios but the discussion here is about the credible relieving cases based on which the relevant PSV should be sized.