50 replies to this topic

[jprocess]

I invite you to review my previous post again. As can be seen I did not mention anything about "Control". I made a comparison between active(instrumentation which trippes some equipment at the onset of very high temperature for the main question and at the onset of very low level for the case study that I mentioned) and passive(properly setting design values for the main question or considering pressure relief for the case study that I mentioned) protective systesm.

For the case study that I mentioned based on your judgement about double jeopardy the simultaneous failure of equipment shutdown system due to very low level and failure of control valve(gas blowby) is unlikely. This case study is similar to main question(Failure of very high temperature vs. failure of very low level and cooling failure vs. gas blowby)

Now let me know who ignore about gas blowby for the mentioned case study?

Your statement about SIL verification is in line with my view. For the case study that I mentioned the designer may consider pressure relief system for downstream equipment or consider SIL rated LCV. This means that the designer is aware about the hazard and do consider (and do not ignore) about these two unrelated failures.

[shan]

Design temperature and design pressure are specified at the most serve process conditions plus safety factor. When you define design temperature and design pressure, process upset scenarios (cooling water failure, instrument malfunction, fire and etc) shall not be considered. Otherwise, all the design temperature values would be 1000+ F to stand for possible fire. Therefore, 32.5 barg design pressure and 85 C design temperature are legitimately values.

PSV is sized for the maximum flow at the relieving pressure. Although block outlet is the governing scenario for the PSV sizing, overpressure caused by cooling water failure is also protected by the PSV.

[fallah]

For the case study that I mentioned based on your judgement about double jeopardy the simultaneous failure of equipment shutdown system due to very low level and failure of control valve(gas blowby) is unlikely. This case study is similar to main question(Failure of very high temperature vs. failure of very low level and cooling failure vs. gas blowby)

Case 1:Cooling failure (cause)---->Overheating of separator (consequence)-----> HH alarm on TI-4012 as safeguard may lead to local shutdown

Case 2:LIC malfunction leading to LCV to be wide open or LL alarm failure (cause)------>Gas blowby (consequence)------>Mechanical stop at specified CV on relevant LCV or putting RO downstream of LCV as safeguard

Two above cases show a different picture compare to what you mentioned.Gas blowby,isn't a cause and is a consequence of LIC/LCV failure and should be prevented by a proper safeguard.

[jprocess]

Design temperature and design pressure are specified at the most serve process conditions plus safety factor. When you define design temperature and design pressure, process upset scenarios (cooling water failure, instrument malfunction, fire and etc) shall not be considered. Otherwise, all the design temperature values would be 1000+ F to stand for possible fire. Therefore, 32.5 barg design pressure and 85 C design temperature are legitimately values.

PSV is sized for the maximum flow at the relieving pressure. Although block outlet is the governing scenario for the PSV sizing, overpressure caused by cooling water failure is also protected by the PSV.

I disagree with you.Please be informed that from the upset contigencies only the fire case can be excluded and the others shall be considered.

[jprocess]

Case 1:Cooling failure (cause)---->Overheating of separator (consequence)-----> HH alarm on TI-4012 as safeguard may lead to local shutdown

Case 2:LIC malfunction leading to LCV to be wide open or LL alarm failure (cause)------>Gas blowby (consequence)------>Mechanical stop at specified CV on relevant LCV or putting RO downstream of LCV as safeguard

Two above cases show a different picture compare to what you mentioned.Gas blowby,isn't a cause and is a consequence of LIC/LCV failure and should be prevented by a proper safeguard.

I did not mention in this manner. I raised very low shutdown as the safeguard(active) and considering gas blowby scenario as passive protection.

This new post by you is in contrast with your previous one. You consider very low shutdown and gas blowby as double contigency.

[fallah]

I did not mention in this manner. I raised very low shutdown as the safeguard(active) and considering gas blowby scenario as passive protection.

This new post by you is in contrast with your previous one. You consider very low shutdown and gas blowby as double contigency.

"gas blowby scenario as passive protection"!!!!

Gas blowby is a CONSEQUENCE of More flow of feed from upstream vessel to downstream vessel due to malfunction of LIC to open relevant LCV more than required.This may lead to overpressurization of downstream vessel.

I didn't consider anything about "very low shutdown and gas blowby" other than what i mentioned in my previous post.Please read it accurately.

I presented Case 2 just for analyzing the gas blowby case to show it is neither a cause nor a passive protection.

[shan]

Design temperature and design pressure are specified at the most serve process conditions plus safety factor. When you define design temperature and design pressure, process upset scenarios (cooling water failure, instrument malfunction, fire and etc) shall not be considered. Otherwise, all the design temperature values would be 1000+ F to stand for possible fire. Therefore, 32.5 barg design pressure and 85 C design temperature are legitimately values.

PSV is sized for the maximum flow at the relieving pressure. Although block outlet is the governing scenario for the PSV sizing, overpressure caused by cooling water failure is also protected by the PSV.

I disagree with you.Please be informed that from the upset contigencies only the fire case can be excluded and the others shall be considered.

Then, what is your agreed design temperature for D-4002? 300 C? What is the next downstream equipment design temperature? 300 C again? How about next after that? If you have a set of go-by P&ID for reference, please check the design temperature downstream a cooler to understand what I mean here.

[Qalander (Chem)]

Design temperature and design pressure are specified at the most serve process conditions plus safety factor. When you define design temperature and design pressure, process upset scenarios (cooling water failure, instrument malfunction, fire and etc) shall not be considered. Otherwise, all the design temperature values would be 1000+ F to stand for possible fire. Therefore, 32.5 barg design pressure and 85 C design temperature are legitimately values.

PSV is sized for the maximum flow at the relieving pressure. Although block outlet is the governing scenario for the PSV sizing, overpressure caused by cooling water failure is also protected by the PSV.

I disagree with you.Please be informed that from the upset contigencies only the fire case can be excluded and the others shall be considered.

Then, what is your agreed design temperature for D-4002? 300 C? What is the next downstream equipment design temperature? 300 C again? How about next after that? If you have a set of go-by P&ID for reference, please check the design temperature downstream a cooler to understand what I mean here.

The discussion is fruitful and yielding for Process safety.
Somehow I don't exactly estimate here through calculation derived from any of the code(s) or standard(s) possibly applicable here and 'Doug' may guide us on that.

However it is envisaged that for Cooling media failure case the vessel or containment in question should have a very short exposure Max. temperature withstanding capability for 300 Celsius

Until any layer of protection ensured to act positively drops the temperature or

positively cuts off the hot stream inflow along with some emergency low temperature purge gas inflow.

This is just a wild thought right now and may be not that accurate;some other learned colleagues will correct through jumping in if Wrong.

[shan]

Dear All-

This refers to attached scheme, wherein regeneration gas is entering at 300 deg C, which is getting cooled in cooling water exchanger to 55 deg C & send to B.L. through regenaration gas separator.

The design temperature of regeneration gas separator is 85 deg (as per criteria of maximum operating +15 deg C). However, the safety valve capacity is decided based on block discharge.

A point is raised for the design temperature of regeneration gas separator in case of cooling water failure.

Can somebody guide me whether design temperature for downstream equipment of cooler shall be raised considering cooling water failure / else what shall be done to safe gaurd the down stream equipment in case of cooling water failure.

Thanks in advance.

My point is simple and clear. Design temperature and design pressure are based on max allowable working temperature and max allowable working pressure. Design temperature and design pressure have noting to do with undesired situations including (cooling water failure, instrument malfunction, fire…). The undesired situations are handled by the designated safety device including sensors, control valves, and PSV’s. Therefore, I vote for D-4002 design pressure 32.5 barg and design temperature 85 C.

[fallah]

My point is simple and clear. Design temperature and design pressure are based on max allowable working temperature and max allowable working pressure. Design temperature and design pressure have noting to do with undesired situations including (cooling water failure, instrument malfunction, fire…). The undesired situations are handled by the designated safety device including sensors, control valves, and PSV’s. Therefore, I vote for D-4002 design pressure 32.5 barg and design temperature 85 C.

Design temperature and design pressure are not based on max allowable working temperature and max allowable working pressure.

When a vessel goes into design it is assigned a coincidental design pressure and temperature based on most severe condition of coincidental internal and external pressure and temperature.These are the maximum/minimum conditions the vessel is expected to experience while in service,and what the engineers will design the vessel to handle.

MAWP/MAWT are the values can be determined only when all factual data of vessel construction is collected and entered into vessel engineering program.These values can never be less than the design pressure and design temperature.

Thus,you can consider the design temperature of downstream separator (D-4002) equal to 85 C just if in risk assessment and HAZOP study it is realized/approved that the adequate safeguard(s) is being considered to prevent that separator subject to high temperature condition may occurr in cooling failure.

[jprocess]

"gas blowby scenario as passive protection"!!!!

You dropped "considering" from my previous post. What I wrote was "I raised very low shutdown as the safeguard(active) and considering gas blowby scenario as passive protection."
So what is wrong with this?

I didn't consider anything about "very low shutdown and gas blowby" other than what i mentioned in my previous post.Please read it accurately.

I read it accurately. You meantioned "Case 2:LIC malfunction leading to LCV to be wide open or LL alarm failure (cause)------>Gas blowby (consequence)------>Mechanical stop at specified CV on relevant LCV or putting RO downstream of LCV as safeguard"
So by this explanation this can be found that you do not consider very low level shutdown in your process design. Am I right? If so, for sure this configuration will be rejected during Hazop.

And if you decide to consider very low liquid level shutdown then based on your justification failure of this shutdown and LIC should be considered as double jeopardy!

[jprocess]

Then, what is your agreed design temperature for D-4002? 300 C? What is the next downstream equipment design temperature? 300 C again? How about next after that? If you have a set of go-by P&ID for reference, please check the design temperature downstream a cooler to understand what I mean here.

As I wrote earlier by definition the Design value is the one that covers all of the normal and upset conditions of the plant. So in this case the design temperature will be 300C(as the maximum anticipated operating temperature) plus a margin based on Design Criteria of the project. The cut off point will be the first downstream ESDV.

[fallah]

You dropped "considering" from my previous post. What I wrote was "I raised very low shutdown as the safeguard(active) and considering gas blowby scenario as passive protection."
So what is wrong with this?

I read it accurately. You meantioned "Case 2:LIC malfunction leading to LCV to be wide open or LL alarm failure (cause)------>Gas blowby (consequence)------>Mechanical stop at specified CV on relevant LCV or putting RO downstream of LCV as safeguard"
So by this explanation this can be found that you do not consider very low level shutdown in your process design. Am I right? If so, for sure this configuration will be rejected during Hazop.

And if you decide to consider very low liquid level shutdown then based on your justification failure of this shutdown and LIC should be considered as double jeopardy!

With or without "considering",gas blowby can not be considered as passive protection.Please correct my understanding if it is wrong.

For your example about gas blowby and your above conclusion refer to the statement in my previous post as:

" I presented Case 2 just for analyzing the gas blowby case to show it is neither a cause nor a passive protection."

[NGL Licensor]

Dear All-

This refers to attached scheme, wherein regeneration gas is entering at 300 deg C, which is getting cooled in cooling water exchanger to 55 deg C & send to B.L. through regenaration gas separator.

The design temperature of regeneration gas separator is 85 deg (as per criteria of maximum operating +15 deg C). However, the safety valve capacity is decided based on block discharge.

A point is raised for the design temperature of regeneration gas separator in case of cooling water failure.

Can somebody guide me whether design temperature for downstream equipment of cooler shall be raised considering cooling water failure / else what shall be done to safe gaurd the down stream equipment in case of cooling water failure.

Thanks in advance.

If cooling water being failed,by TT-4012 probably there will be an action by TI-4012 on high alarm.Knowing this action make help to better clarification.

If TI-4012 on high alarm not followed by an action prevent the hot gas (due to cooling water failure) passing through separator,the design temperature of separator should be 300 C (not 85 C).

Anyway,the safeguard might be closing a SDV located at the regeneration gas inlet to exchanger by alarm high of TI-4012 and set point of 85 C (predefined design pressure of separator).

Hi,

I have much respect to the fruitful discussion on this subject.

Some points wanted to highlight:

-Normally you need to conduct a HAZOP to cover such aspects in specific nodes and with overall picture in mind (up-stream/down-stream process configuration, composition of streams, etc)

-I see that an outlet process temperature control is needed in order to normally keep the regen vessel temperature at 55 C. This will happen by regulating the cooling water flow or its by-pass or combination of both.

-You need to inspect in length the reasons for cooling water failure (normally covered in the HAZOP) and provide the safeguards accordingly

-One of the expected actions, during C.W failure, is to shut-down or by-pass the regen gas heater(depending on the heating configuration)

A.King

[jprocess]

With or without "considering",gas blowby can not be considered as passive protection.Please correct my understanding if it is wrong.

By considering I mean engineering the gas blow by case carefully and providing adequate pressure relief protection.

[jprocess]

Hi,

I have much respect to the fruitful discussion on this subject.

Some points wanted to highlight:

-Normally you need to conduct a HAZOP to cover such aspects in specific nodes and with overall picture in mind (up-stream/down-stream process configuration, composition of streams, etc)

-I see that an outlet process temperature control is needed in order to normally keep the regen vessel temperature at 55 C. This will happen by regulating the cooling water flow or its by-pass or combination of both.

-You need to inspect in length the reasons for cooling water failure (normally covered in the HAZOP) and provide the safeguards accordingly

-One of the expected actions, during C.W failure, is to shut-down or by-pass the regen gas heater(depending on the heating configuration)

A.King

Depending on the philosophy of heat exchanger control, sometimes the designer consider by pass line for heat exchanger. So this can be in line with considering hot gas temperature for setting the design temperature of downstream vessel.

[fallah]

By considering I mean engineering the gas blow by case carefully and providing adequate pressure relief protection.

If you mean as above you are correct.But complementary protection is preventing gas blowby case via line block by SDV activated on LL alarm.

[jprocess]

I am still waiting for experts like JoeWong to drop their ideas here that which design temperature they consider for this case study? The one which ignores the cooling failure or the one which consider this?

[NGL Licensor]

Hi,

I have much respect to the fruitful discussion on this subject.

Some points wanted to highlight:

-Normally you need to conduct a HAZOP to cover such aspects in specific nodes and with overall picture in mind (up-stream/down-stream process configuration, composition of streams, etc)

-I see that an outlet process temperature control is needed in order to normally keep the regen vessel temperature at 55 C. This will happen by regulating the cooling water flow or its by-pass or combination of both.

-You need to inspect in length the reasons for cooling water failure (normally covered in the HAZOP) and provide the safeguards accordingly

-One of the expected actions, during C.W failure, is to shut-down or by-pass the regen gas heater(depending on the heating configuration)

A.King

Depending on the philosophy of heat exchanger control, sometimes the designer consider by pass line for heat exchanger. So this can be in line with considering hot gas temperature for setting the design temperature of downstream vessel.

In this application hot gas by-pass is not workable. I meant a by-pass on the cooling water side to regulate the KO temperature.

[JoeWong]

I am still waiting for experts like JoeWong to drop their ideas here that which design temperature they consider for this case study? The one which ignores the cooling failure or the one which consider this?

Just dropped by and noticed a request here... just drop some opinion...

Case : Cooling water failure (or blocked in) follow by hot gas passing HX.

Two consequences :
i) Cooling water blocked in and heat/vaporise by hot gas. First thread is the overpressure of HX tubeside due to hot gas heating.
ii) Hot gas passed HX and heating downstream equipment. As downstream equipment is designed low (85 degC vs 300 degC of hot gas temp). Following API-14C, the heat source shall be removed. The way is to shut-close SDV upstream of HX (hot gas side). A high temperature trip (TAHH) is required. One shall understand that present TAH (TI-4012) is pre-alarm to alert operator to take necessary actions. Nevertheless, from safeguarding aspect, operator action may not be sufficient due to human factor. Therefore a dedicated TT (TAHH) is required for safeguarding function. This TAHH will be wired to ESD system to protect the downstream system.

Then the next thing is availability and Failure-on-demand of TAHH, consequences & risk analysis, probability derivation for failure of cooling water supply and TAHH, etc. It will be conducted in IPF studies. SIL level will be assigned and SIL level (as provided) will be calculated. 1oo2 or 2oo3 with/wo multiple closing device will be considered...

Another option is to increase of downstream design temperature. I don't see this option fly...Reason being the limit of this high design temperature. It could be excessive.

Some advices :
Don't mix control and safeguarding function
Don't mix double jeopardy with Failure on demand
Don't mix design (D) and maximum allowable working (MAW)

[NGL Licensor]

I am still waiting for experts like JoeWong to drop their ideas here that which design temperature they consider for this case study? The one which ignores the cooling failure or the one which consider this?

Just dropped by and noticed a request here... just drop some opinion...

Case : Cooling water failure (or blocked in) follow by hot gas passing HX.

Two consequences :
i) Cooling water blocked in and heat/vaporise by hot gas. First thread is the overpressure of HX tubeside due to hot gas heating.
ii) Hot gas passed HX and heating downstream equipment. As downstream equipment is designed low (85 degC vs 300 degC of hot gas temp). Following API-14C, the heat source shall be removed. The way is to shut-close SDV upstream of HX (hot gas side). A high temperature trip (TAHH) is required. One shall understand that present TAH (TI-4012) is pre-alarm to alert operator to take necessary actions. Nevertheless, from safeguarding aspect, operator action may not be sufficient due to human factor. Therefore a dedicated TT (TAHH) is required for safeguarding function. This TAHH will be wired to ESD system to protect the downstream system.

Then the next thing is availability and Failure-on-demand of TAHH, consequences & risk analysis, probability derivation for failure of cooling water supply and TAHH, etc. It will be conducted in IPF studies. SIL level will be assigned and SIL level (as provided) will be calculated. 1oo2 or 2oo3 with/wo multiple closing device will be considered...

Another option is to increase of downstream design temperature. I don't see this option fly...Reason being the limit of this high design temperature. It could be excessive.

Some advices :
Don't mix control and safeguarding function
Don't mix double jeopardy with Failure on demand
Don't mix design (D) and maximum allowable working (MAW)

Hi,

Mole sieve unit are installed worldwide. It is an open art and not a licensed technology. The regeneration system and configuration is a very industry standard type.

Knowing that mole sieve regeneration is not on a full time basis (typically 2-3 hrs) ,the high high temperature protection of the KO vessel, in case of CW failure, is normally done by switching off the regen gas heater or activate hot-oil by-pass (in case of regen hot oil heater type).

A.King

[jprocess]

Dear JoeWong

Another option is to increase of downstream design temperature. I don't see this option fly...Reason being the limit of this high design temperature. It could be excessive.

In one of the projects we had hot gas temperature values upto 160C and we used this value to set the downstream equipment design temperature specification. We also considered natural convection of 20% for cases that air cooling without bypass is considered. I agree that 300C is a high value but the other option (high SIL instrumentation) is also costly and the final decision should be made based on judgment between these two options.

How do you interpret excessive word for temprature variable?

[JoeWong]

How do you interpret excessive word for temprature variable?

What i mean was the high design temperature will be extended to many downstream equipment...

[jprocess]

How do you interpret excessive word for temprature variable?

What i mean was the high design temperature will be extended to many downstream equipment...

You mean that you ignore about hot gas temperature and instead consider very high temperature trip?

[jitendraprocess]

good & enhancing knowledge regarding process safety.

Thanks