Dear Sir, Madam
API 521 recommends to use High-integrity safety instrumented system (HISIS) to relax relief load process plan? I hear that in parallel to HISIS, a psv should be installed to protect the equipment against fire case? is there any backup for this assumption?
Regards
A.Bashiri
Ghasem.Bashiri@gmail.com
Full Version: Hisis And Psv
API Standard 521 does NOT recommend the use of HIPS, it only presents this as a an option. Also, if you read through the entire discussion in Appendix E of the new API Standard 521, there are implied pitfalls all over the place and I could easily interpret fire as being one of them.
Think about it, how is a HIPS going to prevent a fire? Perhaps it can be used to minimize the chances and to aid in reducing the effects but I can't see how it can prevent one.
Process safety system evaluation and design also requires the use of common sense and good engineering judgement. If you're looking for back-up for what you've heard (and by the way, where or from whom did you exactly hear this from?), just apply some good old engineering judgement and also re-read the API standard, slowly and real carefully.
Think about it, how is a HIPS going to prevent a fire? Perhaps it can be used to minimize the chances and to aid in reducing the effects but I can't see how it can prevent one.
Process safety system evaluation and design also requires the use of common sense and good engineering judgement. If you're looking for back-up for what you've heard (and by the way, where or from whom did you exactly hear this from?), just apply some good old engineering judgement and also re-read the API standard, slowly and real carefully.
QUOTE (pleckner @ Oct 18 2007, 05:54 AM) 
API Standard 521 does NOT recommend the use of HIPS, it only presents this as a an option. Also, if you read through the entire discussion in Appendix E of the new API Standard 521, there are implied pitfalls all over the place and I could easily interpret fire as being one of them.
Think about it, how is a HIPS going to prevent a fire? Perhaps it can be used to minimize the chances and to aid in reducing the effects but I can't see how it can prevent one.
Process safety system evaluation and design also requires the use of common sense and good engineering judgement. If you're looking for back-up for what you've heard (and by the way, where or from whom did you exactly hear this from?), just apply some good old engineering judgement and also re-read the API standard, slowly and real carefully.
Think about it, how is a HIPS going to prevent a fire? Perhaps it can be used to minimize the chances and to aid in reducing the effects but I can't see how it can prevent one.
Process safety system evaluation and design also requires the use of common sense and good engineering judgement. If you're looking for back-up for what you've heard (and by the way, where or from whom did you exactly hear this from?), just apply some good old engineering judgement and also re-read the API standard, slowly and real carefully.
As designer, we are trying our best to avoid using HIPS due to reliability, availability and maintainability of the HIPS system. However, certain scenario will really push us to use HIPS.
Let take an example. A HP separator designed for 50 barg with separated liquid feeding a LP separator designed for 15 barg. Obviously there is a High pressure (HP) - Low Pressure (LP) interface here. Pressure Relief Device is generally required to protect the LP system. However, sometime the HP separator contain a very large liquid inventory as compare to LP separator. In the event, liquid control valve failure (HP separator liquid control valve) will leads to large amount of liquid from HP separator occupy the LP separator. Sudden large amount of liquid filling LP separator may leads to sudden large liquid surging to the LP separator. It is very difficult to quantify the impact of this liquid surge. Experience indicated that surging pressure could be few time higher than the LP separator design pressure. Under this scenario, HIPS may be required to be provided at the Liquid line.
Provision of HIPS on the liquid line will not protect the LP separator from other overpressure scenario e.g. external fire attack, backflow, etc. Those Pressure relief device still required to be provided on the LP separator for overpressure protection.
I do agree with Phil last paragraph "Process safety system evaluation and design also requires the use of common sense and good engineering judgement. If you're looking for back-up for what you've heard (and by the way, where or from whom did you exactly hear this from?), just apply some good old engineering judgement and also re-read the API standard, slowly and real carefully.". Proper engineering analysis and judgment is absolutely required.
JoeWong
Dear JoeWong,
Why do not you recommend the usage of HIPS:
"As designer, we are trying our best to avoid using HIPS due to reliability, availability and maintainability of the HIPS system."
And what do you mean by backflow in your post?
"povision of HIPS on the liquid line will not protect the LP separatr from other overpressure scenario e.g. external fire attack, backflow, etc. Those Pressure relief device still required to be provided on the LP separator for overpressure protection."
Why do not you recommend the usage of HIPS:
"As designer, we are trying our best to avoid using HIPS due to reliability, availability and maintainability of the HIPS system."
And what do you mean by backflow in your post?
"povision of HIPS on the liquid line will not protect the LP separatr from other overpressure scenario e.g. external fire attack, backflow, etc. Those Pressure relief device still required to be provided on the LP separator for overpressure protection."
QUOTE (jprocess @ Nov 12 2007, 10:05 AM)
Why do not you recommend the usage of HIPS:
"As designer, we are trying our best to avoid using HIPS due to reliability, availability and maintainability of the HIPS system."
"As designer, we are trying our best to avoid using HIPS due to reliability, availability and maintainability of the HIPS system."
HIPS required SIL4. The CAPEX is high. Of course, this can be compensated by low capacity disposal system. HIPS system demand high reliability & availability and frequent testing of this facilities to maintain/enhance it reliability & availability. To maintain frequent quality testing could be a difficult task for certain operator. It also subject to the awareness and education level of operator which is rather subjective, unpredictable and human oriented. Thus from management perspective, HIPS should be avoided if possible.
QUOTE
And what do you mean by backflow in your post?
"povision of HIPS on the liquid line will not protect the LP separatr from other overpressure scenario e.g. external fire attack, backflow, etc. Those Pressure relief device still required to be provided on the LP separator for overpressure protection."
"povision of HIPS on the liquid line will not protect the LP separatr from other overpressure scenario e.g. external fire attack, backflow, etc. Those Pressure relief device still required to be provided on the LP separator for overpressure protection."
Assuming there is a pump transferring liquid from LP separator to a high pressure (HP) system, HIPS provided on LP separator inlet to avoid overpressure from HP system at feed will not protect LP separator from HP system backflow to LP separator in case of pump discharge check valve failure. On the other hand, providing a PSV on the LP separator will protect LP separator for both overpressure scenarios.
JoeWong
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