10 replies to this topic

[aniljani]

Hi,

 

I am working on Distillation column PSV sizing calc. Reboiler is kettle type. One of the PSV credible scenario is reboiler tube rupture case. My lead says as per recent API amendments, no need to consider tube rupture case for kettle reboiler side.. Please clarify whether this credit can be taken??

[Bobby Strain]

Why don't you look at the amendment?

 

Bobby

[himanshu.ch]

Dear All,

 

I am unable to find the amendment which talks about exclusion of tube rupture for kettle reboilers. Can someone help me with this please?

 

Also, I was informed that the tube rupture is also not applied for vacuum service condensers due to large volume of equipment which can allow cooling water to come out without overpressurization. Kindly help me with this too.

 

Regards

Himanshu

[latexman]

I've never heard of a kettle reboiler exclusion to tube rupture scenario, maybe that's why you can't find it.  I searched API 520 I & II and 521, and saw nothing.  Has anyone else  seen/used this exclusion?

 

Can you provide the standard for this vacuum service condenser exclusion to tube rupture scenario?  Again, I've never heard of it.  Has anyone else  seen/used this exclusion?  When a credible scenario results in a design no one can afford, one usually focuses heavily on the prevention of said scenario.

 

This is all very general.  There are some situations that are RAGAGEP that preclude the tube rupture scenario, but more details are needed.  If you provide enough details to evaluate/size your tube rupture scenario, then a better answer might be possible.

[Pilesar]

Ask your lead to show you supporting documentation. If the lead is authorized by your employer to identify that exchanger tube rupture is an acceptable risk for the company, then confirm the instructions clearly in writing. There are legitimate reasons that a reboiler tube rupture might not result in overpressure. Written documentation should be standard procedure. How much trouble would it be to just include the scenario and calculate the results anyway? If it is not the controlling case, then it would be easier to just do the calcs instead of figuring out how to avoid doing them.

[breizh]

HI,

If you need to perform calculation for similar case, let you consider this link:

https://www.eng-tips....cfm?qid=487587

 

As others said check with your lead the reference of the amendment.

Breizh

[fallah]

 

I am working on Distillation column PSV sizing calc. Reboiler is kettle type. One of the PSV credible scenario is reboiler tube rupture case. My lead says as per recent API amendments, no need to consider tube rupture case for kettle reboiler side.. Please clarify whether this credit can be taken??

 

Hi,

 

For the case you mentioned, in one hand likely the design pressure of the tube and shell sides are equal or close together; hence no need to consider tube rupture case...and:

 

On the other hand, even if the design pressure of both sides are different; the distillation column plus reboiler system is normally such that due to having no obstacle (valve, inline component,...) between the reboiler and the column, the PSV on the column can handle the relief load of the probable tube rupture case hence such case can be ignored among credible ones...

[breizh]

Hi Naser,

We have no information about the steam pressure, the operating pressure and the boiling point of the products.

I've been operating columns under vacuum with a steam pressure above 11 bars where the boiling point of the product was 175 C.

More information from the OP is required.

Breizh

[fallah]

Hi Naser,

We have no information about the steam pressure, the operating pressure and the boiling point of the products.

I've been operating columns under vacuum with a steam pressure above 11 bars where the boiling point of the product was 175 C.

More information from the OP is required.

Breizh

Hi Breizh,

 

What i have provided for OP query is general and hasn't any dependence to steam/product properties and characteristics...

[shvet1]

API 521-2020

 

4.4.14.2 Shell-and-tube Heat Exchangers

4.4.14.2.1 Pressure Considerations

Complete tube rupture, in which a large quantity of high-pressure fluid flows to the lower-pressure heat exchanger side, is a remote but possible contingency. Minor leakage can seldom overpressure a heat exchanger during operation; however, such leakage occurring where the low-pressure side is closed in can result in overpressure. Loss of containment of the low-pressure side to atmosphere is unlikely to result from a tube rupture where the pressure in the low-pressure side (including upstream and downstream systems) during the tube rupture does not exceed the corrected hydrotest pressure (see 3.1.19 and 4.2.2). The user may choose a pressure other than the corrected hydrotest pressure, given that a proper detailed mechanical analysis is performed showing that a loss of containment is unlikely. The use of maximum possible system pressure instead of design pressure may be considered as the pressure of the high-pressure side on a case-by-case basis where there is a substantial difference in the design and operating pressures for the high-pressure side of the heat exchanger.

Pressure relief for tube rupture is not required where the low-pressure heat exchanger side (including upstream and downstream systems) does not exceed the criteria noted above. The tube rupture scenario can be mitigated by increasing the design pressure of the low-pressure heat exchanger side (including upstream and downstream systems), and/or ensuring that an open flow path can pass the tube rupture flow without exceeding the stipulated pressure, and/or providing pressure relief.

 

ExxonMobil's std. XVC

 

3 DEFINITIONS

Design Contingency

An abnormal condition including maloperation, equipment malfunction, or other event which is not planned, but is foreseen to the extent that the situations involved are considered in establishing equipment design conditions.

Remote Contingency

An abnormal condition which could result in exceeding design pressure at the coincident temperature, but whose probability of occurrence is so low it is not considered as a design contingency. Note that temperatures above the design temperature may also be permitted under remote contingency conditions.

...

4 SUMMARY OF SPECIFIC EXXON MOBIL REQUIREMENTS

...

9. Heat exchanger tube rupture or leakage shall be considered as a remote contingency. Overpressure protection of the low pressure side need not be provided if the proof test pressure of the low pressure side, including attached piping and interconnected equipment is equal to or greater than the design pressure of the high pressure side. If this condition is not satisfied, overpressure protection may be required unless it can be shown that the relief capacity through the piping and equipment connected to the low pressure side is sufficient to prevent the pressure in the low pressure side from exceeding the proof test pressure.

 

Shell's std. DEP 80.45.10.11

 

4.2 HEAT EXCHANGER INTERNAL FAILURE

4.2.1 General

The heat exchanger internal failure scenario involves evaluating the consequences of a tube rupture in a shell-and-tube heat exchanger or an internal failure in other types of heat exchangers such as plate and frame, printed circuit, brazed aluminium heat exchangers. This scenario also includes vessel/tank heating and cooling coils that could rupture. Regardless of the design, the consequence of a leak shall also be considered (e.g., process incompatibility, overpressure if equipment is isolated).

1. Shell-and-tube heat exchanger system (exchanger and attached equipment) SHALL [PS] have overpressure protection if exchanger tube rupture is considered viable and the hydraulic limits of the system's relief path cause the system pressure to exceed the corrected hydrotest pressure.

2. Tube rupture shall be considered a viable overpressure scenario only if the exchanger high side design pressure is greater than the corrected hydrotest pressure of the low side system. The viability of a tube rupture shall be considered for downstream systems as well. Where the system design pressures meet this criterion, the tube rupture case is no longer an overpressure scenario for the heat exchanger, but the upstream and downstream systems still need to be considered both for overpressure and for other consequences (e.g. contamination).

...

5. The internal rupture of double pipe exchangers shall not be considered viable provided the double pipe exchangers are constructed from piping components. 

NOTE: Hairpin exchangers with tube bundles are not considered double pipe exchangers.

 

JGC's std. 210-120-1-40

 

6.10 Tube Rupture of Heat Exchanger

The low pressure side of heat exchangers (including upstream and downstream systems) should be protected from the overpressure caused by the tube rupture, if the hydrotest pressure of the low pressure side is lower than the design pressure of the high pressure side.

As per ASME Sec VIII Div 1 UG-99, hydrotest pressure is at least equal to 130% of the design pressure multiplied by the lowest ratio of the stress value of the material for the test temperature to the stress value for the design temperature. However, if hydrotest pressure of the system is not yet fixed, it can be assumed that overpressure protection is not required if design pressure of the low pressure side is at least 10/13 of the design pressure of high pressure side (this can be referred to as the “10/13 rule”). 

For double pipe exchangers using schedule pipe or heavier gauge tube for the inner pipe, the overpressure due to tube rupture is not considered, since inner tube is not likely to rupture.

 

BP's std. GP 44-70

 

8.1.2. Burst tube condition

...

c. If maximum operating pressure on high pressure side is greater than corrected test pressure on low pressure side, the low pressure side of the exchanger shall have relief protection for a burst tube.

[shvet1]

Describe process side fluid