Consider These Safety Instrumented System Best Practices-Books Pdf

CONSIDER THESE SAFETY INSTRUMENTED SYSTEM BEST PRACTICES
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Consider HIPS for Reactive Processes 3, Such safety instrumented systems offer advantages. over pressure relief valves, Get the Most Out of Your HART SIS 7. Several HART parameters and best practices ensure, its capabilities are fully realized. Perform Proof Tests with Confidence 14, Modern method improves efficiency reduces errors. and meets compliance requirements, Emerson Process Management 19.
www emersonprocess com, t PREVIOUS PAGE 2 NEXT PAGE u. Consider HIPS for Reactive Processes, Such safety instrumented systems offer advantages over pressure relief valves. By Angela E Summers Ph D P E president of SIS TECH Solutions. AN UNCONTROLLED reaction can cause over Reactive chemicals and their associated processes. pressure in a vessel and thus lead to significant safety present complex scenarios for PRV design Small de. hazards Industry standards from the American viations in reactant concentration or reaction condi. Petroleum Institute and the American Society of tions can put the reaction on a path that the process. Mechanical Engineers provide criteria for the design design control system and operator procedures can. and protection of vessels from rupture and damage not adequately manage Unfortunately many PRVs. caused by excess pressure are improperly sized for reactive processes because. Pressure relief valves PRVs generally are used to relief rate calculations often are based on a design. meet API Recommended Practice 521 1 and ASME and operational envelope that ignores potential reac. Boiler and Pressure Vessel Code Section VIII 2 tion paths that are not well understood. However safety instrumented systems SIS called Numerous incidents including those at Georgia. high integrity protection systems HIPS provide an Pacific Columbus Ohio 1997 Morton Inter. attractive alternative in many cases This article dis national Paterson N J 1998 Concept Sciences. cusses how to assess design and implement an HIPS Hanover Township Pa 1999 Chevron Phillips. Chemical Co Pasadena Texas 1999 and BP, USUAL PRACTICE Amoco Augusta Ga 2001 have proved that. In conventional design the primary means of protec there are reactive scenarios under which a PRV is. tion against vessel overpressure is a PRV It is a simple ineffective They point to a number of general sce. mechanical device that opens when pressure exceeds narios in which PRVs should not be considered. a set level The pressure is relieved through the PRV R eaction generates pressure at an uncontrol. to the atmosphere or to a contained collection system lable rate e g runaway reaction or decomposi. such as a flare scrubber or thermal oxidizer tion such that an impractically large vent area. PRVs boast relatively high integrity as long as they is required or in the worse case an adequately. are properly sized located inspected and maintained sized PRV is not possible. Table 1 summarizes reliability data for a single valve Reaction takes place in a localized area e g hot. relief system as published in Guidelines for Process spots propagating pressure at a rate so fast that. Equipment Reliability Data 3 It shows substantial containment is lost before PRV is able to act. uncertainty in the failure to open on demand Reaction occurs in a localized area raising. t PREVIOUS PAGE 3 NEXT PAGE u, temperature above thermal decomposition point PRV FAILURE TO OPEN ON DEMAND. and causing an internal detonation or fire, Reaction produces during normal operation PRV TYPE FAILURE TO OPEN ON DEMAND.
materials that partially or completely block Lower Mean Upper. PRVs and Spring Operated 7 90E 06 2 12E 04 7 98E 04. Polymerization reaction continues as material is, Pilot Operated 9 32E 06 4 15E 03 1 82E 02. being relieved through PRV into lateral headers, plugging the relief device or lateral header. Thus the very nature of the reactive process often to high pressure Examine all reaction paths. makes a PRV impractical For such cases HIPS including those that may require multiple errors. should be investigated as a means to supplement or failures to begin propagating Once the reac. the PRV for overpressure protection tion paths are understood HIPS can be designed. to address each reaction scenario In many cases, HAZARD ANALYSIS only one or two HIPS are required for mitigation. Successful implementation must be based on a haz of all potential reaction scenarios. ard analysis of each potential overpressure scenario. The analysis should follow a structured systematic DETAILING CRITICAL CONDITIONS. approach using a multidisciplinary team It should A safety requirement specification SRS describes. document the event propagation from the initiat how and under what conditions the HIPS will. ing cause to the final consequence also referred to mitigate each overpressure scenario it includes a. as the overpressure scenario The analysis must functional logic description with trip set points. examine operating and upset conditions that result and device fail safe state Choosing when and. in overpressure It must include a thorough review under what conditions to trip the unit is probably. of each step involved in startup and shutdown the most difficult decision to make in the design. in addition to normal operation For batch and of the HIPS For reactive processes the design is. semi batch processes scrutinize each step of the often complicated by the process dynamics and by. operation using typical deviations and batch intricate process variable interactions. oriented deviations such as skipped steps steps out HIPS design may use single process variables. of sequence steps incomplete steps at wrong time when the reaction path is relatively easy to detect For. recipe incorrect etc example on high temperature the HIPS will stop the. The analysis should include a detailed ex catalyst feed or on high pressure it will inject reaction. amination of reactive scenarios and brainstorm kill solution Single process variables also can prevent. ing on potential reaction paths that could lead the start up of the reactor under unsafe operational. t PREVIOUS PAGE 4 NEXT PAGE u, REFERENCES, 1 Guide for Pressure Relievin and Depressuring Systems. Recommended Practice 521 American Petroleum Insti, tute Washington D C 1997.
2 Boiler and Pressure Vessel Code section VIII Pressure. Vessels American Society of Mechanical Engineers, New York N Y 1999. 3 Guidelines for Process Equipment Reliability Data. Center for Chemical Process Safety American Institute. conditions For example the catalyst cannot be added of Chemical Engineers New Yor N Y 1989. until a fixed volume of solvent which serves as a heat 4 Functional Safety Electrical Electronic Programmable. sink is in the reactor Electronic Safety Related Systems Document IEC. Multiple process variables are used when the 61508 International Elecrotechnical Commission Ge. reaction path is more complex These HIPS often use neva Switzerland 1998. flow mass ratios temperature pressure relationships 5 Summers A E High Integrity Pressure Protective Sys. and kinetic calculations While it is best to try to keep tems in Instrument Engineers Handbook 3rd ed. the HIPS as simple as possible if the reaction paths CRC Press Boca Raton Fla 2002. are intricate the HIPS complexity will escalate 6 Summers A E Using Instrumented Systems For Over. When using reactor kill systems it may be pos pressure Protection Chem Eng Prog 95 p 85 Nov. sible to use preemptive interlocks to prevent the reac 1999. tion from progressing to the point where it must be. killed These interlocks may close reactor feeds open. a pressure control vent or close catalyst valves If the Integrity Level SIL and anticipated testing. temperature or pressure continues to increase after the interval At a minimum the integrity of the HIPS. preemptive interlock a reactor kill is initiated By us should equal that of a PRV The data in Table 1. ing a preemptive interlock the plant is able to recover implies that the HIPS should be designed to meet. more quickly from the process upset and suffer less either SIL 2 or SIL 3 depending upon the type of. production loss and downtime PRV However bear in mind that the failure modes. The potential rate of pressure escalation must of a PRV and the HIPS differ A PRV that fails to. be compared to the HIPS response time to ensure operate at the set pressure nevertheless may operate. that it is fast enough to prevent vessel overpres at a higher pressure whereas HIPS is more likely. sure The HIPS response time must be evaluated to fail completely The failure to open on demand. by considering the time it takes to sense that there uncertainty coupled with the difference in the fail. is an unacceptable process condition the scan rate ure modes results in the majority of users setting. and data processing time of the logic solver and an SIL 3 target for the HIPS. closure speed of the final element The valve speci. fication must include the acceptable leakage rate INTEGRITY AND ARCHITECTURE. because this affects potential downstream pressure It is important to recognize that the HIPS. and relief loading The valve actuator must provide consists of the entire instrument loop from the. sufficient driving force to close the final element field sensor through the logic solver to the final. under the worst case upset pressure condition elements along with support systems required for. The SRS also includes documentation of the successful HIPS functioning such as power air. safety integrity requirements including the Safety or gas supplies. t PREVIOUS PAGE 5 NEXT PAGE u, Process sensors The process variables commonly The HIPS must provide an installation that is as. measured in HIPS are pressure temperature and safe or safer than the PRV it replaces To document. flow Most HIPS applications require one out of that this has been achieved the complete design and. two 1oo2 or 2oo3 voting transmitters for all field operation of the HIPS should be quantitatively veri. inputs Redundant inputs enable the incorpora fied to ensure it meets the required integrity HIPS. tion of input diagnostics significantly increasing typically are SIL 3 SIS and are often the only layer. the integrity of the field inputs Separate process of protection against the overpressure event Conse. connections also are required to decrease common quently many users require an independent third. cause faults such as plugged process taps party evaluation of the appropriateness of the design. Logic solver This hardware must meet the required and the determination of the SIL. SIL which often means that it must comply with, SIL 3 performance requirements as provided in IEC AN ATTRACTIVE ALTERNATIVE. 61508 4 The logic solver can be relays solid state or HIPS can be used to safely mitigate potential reac. programmable electronic systems PES If a PES is tive overpressure scenarios As with any instru. used it must provide a high level of self diagnostics mented system good design depends upon good. and fault tolerance Redundancy of signal paths and specification For HIPS the origin of the design is. logic processing is necessary and the trip output the process hazard analysis which must identify all. function must be configured as de energize to trip overpressure scenarios Then the HIPS is designed. Final elements HIPS must use a minimum of to handle these scenarios HIPS is often the last. dual final elements in a 1oo2 configuration The line of defense so its failure during a reactive. final elements typically are either relays in the mo scenario will result in loss of containment Conse. tor control circuit for shutdown of motor operated quently ensuring the integrity of the HIPS through. valves compressors or pumps or fail safe valves proper field design device testing and maintenance. opened or closed using solenoids in the instrument is mandatory for safe operation. air supply When valves are used both valves must, be dedicated block valves ANGELA E SUMMERS Ph D P E is president of SIS TECH. Solenoid operated valves solenoids configured Solutions Houston Texas a consulting and engineering firm. as de energize to trip are used to actuate the block specializing in safety instrumented systems. valves The solenoid s should be mounted as close, to the valve actuator as possible to decrease the Acknowledgment This paper is based on a presenta.
required transfer volume for valve actuation Finally tion made at the 6th Annual Symposium of the Mary. the exhaust ports should be as large as possible to Kay O Connor Process Safety Center College Station. increase the speed of the valve response Texas Oct 28 29 2003. t PREVIOUS PAGE 6 NEXT PAGE u, Get the Most Out of Your HART SIS. Several HART parameters and best practices ensure its capabilities are fully realized. By Alan Harris Emerson Process Management, HART DIAGNOSTICS in safety instrumented sys Historization of HART alarms can be recorded. tem SIS field devices have been used for many years with the same tool as the BPCS and SIS alarms. by several different SIS vendors HART diagnostics Th. e alarm banner on the operator graphics can, provide much more information on the health of a show HART alarms which will quickly alert the. field device than can be determined from a standard operator of critical devices that are unhealthy and. 4 20 mA signal For this reason greater safety inte require greater monitoring from the operator. grated level SIL by turning Dangerous Undetected Different HART signals can be used to monitor. failures into Dangerous Detected failures and longer and alarm various conditions in the field without. Such safety instrumented systems offer advantages over pressure relief valves Get the Most Out of Your HART SIS 7 Several HART parameters and best practices ensure its capabilities are fully realized Perform Proof Tests with Confidence 14 Modern method improves efficiency reduces errors and meets compliance requirements AD INDEX Emerson Process Management 19 www emersonprocess com 3

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