ARNOLD, K. (1999). Design of Gas-Handling Systems and Facilities (2nd ed.) Episode 2 Part 8 docx

Table 14-5 Safety Device SymbolsSensing and Self-Acting Devices Instrument Society of America I.S.A.Flow Safety ValveBurner Safety LowAnalyzer Safety HighFlow Safety HighFlow Safety LowL

Figure 14*6 Function chart.

Table 14-5 Safety Device Symbols

Sensing and Self-Acting Devices

Instrument Society

of America (I.S.A.)Flow Safety ValveBurner Safety LowAnalyzer Safety HighFlow Safety HighFlow Safety LowLevel Safety HighLevel Safety Low

(table continued)

or Safety HeadPressure- VacuumRelief ValvePressure- VacuumRelief Manhole Cover

VentVacuum Relief ValveRupture Disc

or Safety HeadFusible MaterialHigh Temperature SensorLow Temperature SensorFlame or StackArrestor

Pressure Safety HighPressure Safety LowPressure Safety Valve

Pressure Safety ElementPressure Safety ValvePressure Safety ValveNone

Pressure Safety ValvePressure Safety ElementTemperatureSafety ElementTemperature Safety HighTemperature Safety Low

None

(table continued on next page)

Table 14-5 (Continued) Safety Device Symbols

Sensing and Self-Acting Devices

Safety Device Designation Symbol

Infrared)Heat Dector(Thermal)Smoke Detector(lonization)FusibleMaterialCombustible GasDetector

Instrument Society

of America (I.S.A.)

TemperatureSafety High

TemperatureSafety ElementAnalyzerSafety High

Combination Device

(table continued)

Table 14-6 Component Identification

Common Code Component Modifiers Code Component _

A Atmospheric Vessel BH, BJ, BM AA Bi Directional User Assigned

(Ambient Temperature) AB Blowcase Identification Unique

B Atmospheric Vessel AP, BC, BK, BM AC Boiler to Equipment at

(Heated) AD Coalescer location

C Compressor AR, AS, BA, ZZ AE Compressor

D Enclosure AE, AN, AU, BB AF Contactor

E Fired or Exhaust AL, AW, BN AG Control Unit

Heated Component AH Departing

F Flowline A1-A9 AJ Filter

G Header AR, AS, AT, AY, AZ AK Filter-Separator

H Heat Exchanger BG AL Forced Draft

J Injection Line AR, AS, AT AM Free water Knockout

K Pipeline AA, AH, AQ AN Generator

L Platform AG AP Heater

M Pressure Vessel AB, AD, AF, AJ, AQ Incoming

(Ambient AK, AM, AV, AR Injection, Gas

Temperature) BD, BF, BH, AS Injection, Gas Lift

BJ, BL, BM AT Injection, Water

N Pressure Vessel AC, AF, AM,AP AU Meter

(Heated) BC, BD, BG, AV Metering Vessel

BJ, BK AW Natural Draft

P Pump AX, BA, BE AX Pipeline

Q Wellhead AR, AT, AY, AZ AY Production, Hydrocarbon

Z Other AZ Production, Water

A1-A9 Flo wline Segment

418 Design of GAS-HANDLING Systems and Facilities

(text continued from page 410)

HAZARDS ANALYSIS

A hazards analysis is a systematic procedure for identifying potentialhazards which could exist in a facility, evaluating the probability andconsequence associated with the hazard, and either reducing the proba-bility or mitigating the consequence so that the overall risk associatedwith the hazard is "acceptable." The different hazards analysis techniquescan be applied at various stages during the course of the project to assessand mitigate potential hazards during design, construction and operations

of the facility

Types of Hazards Analysis

Hazards analysis techniques fall in two broad categories Some niques focus on hazards control by assuring that the design is in compli-ance with a pre-existing standard practice These techniques result fromprior hazards analysis, industry standards and recommended practices,results of incident and accident evaluations or similar facilities Othertechniques are predictive in that they can be applied to new situationswhere such pre-existing standard practices do not exist

tech-The most common hazards control technique is a "checklist." tech-Thechecklist is prepared by experienced personnel who are familiar with thedesign, construction and operation of similar facilities Checklists are rel-atively easy to use and provide a guide to the evaluator of items to beconsidered in evaluating hazards API RP 14J has examples of twochecklists which can be used to evaluate facilities of different complexi-

ty Because production facilities are very similar and have been the ject of many hazard analyses, a checklist analysis to assure compliancewith standard practice is recommended for most production facilities.The actual procedure by which the checklist is considered and the man-ner in which the evaluation is documented to assure compliance variesfrom case-to-case

sub-The most common predictive technique which is used to analyze ities which contain new equipment or processes, or where there is anunusually high risk to personnel or the environment is the Hazard andOperability technique or "HAZOP." A HAZOP study requires a team offive to ten multi-discipline personnel consisting of representatives fromengineering, operations, and health, safety, and environmental staff The

facil-Safety Systems 419

facility is broken down into "nodes" (usually a major piece of equipmentand its associated piping, valves and instrumentation), and an experi-enced team leader guides the team through an analysis of each nodeusing a predetermined list of "guide words" and "process parameters."For example, the guide word "LOW" and process parameter "PRES-SURE" results in questions being asked as to potential causes for lowerthan design pressure at the node If the condition is possible, effects areanalyzed and, if necessary, methods of mitigation are added until the risk

is deemed acceptable Although this method is time consuming, it proves

to be a thorough method of analysis and is effective for a new processwhich has never been analyzed before or for a known process whichincorporates new equipment However, a checklist should be used in con-junction with a HAZOP to assure that compliance with standard practice

is not inadvertently overlooked by the HAZOP team

Problems Commonly Encountered

There are several problem areas which seem to appear often in theresults of hazards analyses The most common are:

1 Relief Valve Sizes

Relief valves are often seen to be undersized for the required ing rate, due either to poor initial design or changes in the processconditions which occurred during design The most common systemproblem is that the relief valve was adequately sized for blockeddischarge but not sized for the flowrate that could occur as a result

reliev-of a failure in the open position reliev-of an upstream control valve (i.e.,gas blowby) See Chapter 13

2 Open and Closed Drains

Another common problem area is having open and closed drain tems tied together Liquid which drains from pressure vessels

sys-"flash" at atmospheric pressures giving off gas If this liquid flows

in the same piping as open drains, the gas will seek the closest exit

to atmosphere it can find, causing a potential fire hazard at any opendrain in the system

Many accidents have occurred where gas has migrated through thedrain system to an unclassified area where welding, or other hotwork, was being performed See Chapter 15

420 Design of GAS-HANDLING Systems and Facilities

3, Piping Specification Breaks

Piping pressure ratings should be designed so that no matter whichvalve is closed, the piping is rated for any possible pressure it could

be subjected to, or is protected by a relief valve

When a spec break is taken from a higher to a lower MAWP, theremust be a relief valve on the lower pressure side to protect the pipingfrom overpressure The relief valve can be either on the piping or,more commonly, on a downstream vessel Spec break problems mostcommonly occur where a block valve exists on a vessel inlet, orwhere a bypass is installed from a high pressure system, around thepressure vessel which has a relief valve, to a lower pressure system

4 Electrical Area Classification

Another common mistake often uncovered is electrical equipmentwhich is not consistent with the design area classification SeeChapter 17

SAFETY MANAGEMENT SYSTEMS

A hazards analysis by itself cannot assure that an adequate level forsafety is provided for a facility unless the hazard analysis is included aspart of a comprehensive safety management system In the United Statesevery facility handling highly hazardous chemicals, including someonshore production facilities and most gas plants, must have a ProcessSafety Management (PSM) Plan in place Offshore operators have devel-oped a voluntary safety management system presented in API RP 75,

"Recommended Practices for Development of a Safety and tal Management Program for Outer Continental Shelf (OCS) Operationsand Facilities" (SEMP), which describes the elements which should beincluded in a safety management plan

Environmen-The requirements of both PSM and SEMP are, from a practical point, identical and thus, SEMP can easily be applied to onshore facilities

stand-as well stand-as offshore facilities The bstand-asic concepts of SEMP are stand-as follows:

Safely and Environmental Information

Safety and environmental information is needed to provide a basis forimplementation of further program components such as operating proce-dures and hazards analysis Specific guidelines as to what information isneeded are contained in API RP 14J

Safety Systems 421

Hazards Analysis

This subject is addressed in the previous section of this chapter

Specif-ic guidelines for performing hazards analysis are contained in API RP 14J

Management of Change

Management of Change is a program that helps to minimize accidentscaused by changes of equipment or process conditions due to construc-tion, demolition, or modification Procedures should be set up to identifythe various hazards associated with change All changes, although some-times minor, can result in accident and/or injury if proper steps are notimplemented to make operators aware of the differences Changes infacilities as well as changes in personnel should be managed to maintainthe safety of all personnel and the environment

Operating Procedures

The management program should include written facility operatingprocedures These procedures should provide ample instruction for soundoperation and be consistent with the safety and environmental informa-tion Procedures should be reviewed and updated periodically to reflectcurrent process operating practices Procedures provide the means foreducation of new employees about the process and provide education toall employees on new equipment and practices

Safe Work Practices

A disproportional amount of accidents occur during construction andmajor maintenance activities Safe work practices are written with this inmind and, as a minimum, should cover the following:

• Opening of equipment or piping,

• Lockout and tagout of electrical and mechanical energy sources,

« Hot work and other work involving ignition sources,

• Confined space entry, and

«Crane operations

Training

Training for new employees and contractors, and periodic training ofexisting employees is necessary to educate personnel to be able to per-

422 Design of GAS-HANDLING Systems and Facilities

form their work safely and to be aware of environmental considerations.Training should address the operating procedures, the safe work prac-tices, and the emergency response and control measures

Assurance of Quality and Mechanical Integrity of Critical Equipment

Procedures for assurance of quality in the design, fabrication, tion, maintenance, testing and inspection for critical equipment arerequired Safety requires that critical safety devices must operate asintended and process system components must be maintained to be able

installa-to contain design pressures

Pre-startup Review

A pre-startup safety and environmental review should be performed onall modified or newly constructed facilities

Emergency Response and Control

An Emergency Action Plan should be established, assigning an gency control center and appropriate personnel for emergency response.Drills should be carried out to assure all personnel are familiar with theseplans

emer-Investigation of Incidents

An investigation is required if an incident involving serious safety orenvironmental consequences or the potential for these consequencesoccurs The purpose of such investigation is to learn from mistakes madeand provide corrective action Investigations should be performed byknowledgeable personnel and should produce recommendations for saferworking conditions

Audit of Safety and Environmental Management Program Elements

Periodically, the SEMP elements should be audited to evaluate theeffectiveness of the program Auditing should be conducted by qualifiedpersonnel through interviews and inspections If audits consistently find

no deficiencies in the program, then management should conclude that

Safety Systems 423

the audit is not in itself being done properly, as there are always ments that can be made in a safety management system

improve-SAFETY CASE AND INDIVIDUAL RISK RATE

The overall system for safety described above can be called the "APISystem," It is based on a series of API Standards and RecommendedPractices which can be summarized as a four step system with each suc-ceeding step encompassing the preceding steps:

1 Design and maintain a system for process upset detection and down—RP 14C

shut-2 Design and select hardware with known reliability and mechanicalintegrity to contain pressure and mitigate failure consequences—allother API RP 14 series standards

3 Follow system design concepts, documentation needs and hazardsanalysis requirements—RP 14J

4 Develop a management of safety system—RP 75

This system has proven to provide adequate levels of safety in the Gulf

of Mexico and other similar areas where it is possible to abandon thelocation during a catastrophic event In the North Sea where harsh envi-ronmental conditions exist, a different approach to safety has evolvedwhich is based on developing a Safety Case and calculating an IndividualRisk Rate (IRR) to show that the risk to any individual working in thefacility is As Low As Reasonably Practicable (ALARP)

A Safety Case is a narrative that literally makes the case that an quate level of safety has been reached for an installation It requires look-ing at all potential hazards which could lead to a loss of the installation, aloss of life, or a major pollution event A risk analysis is performed oneach hazard evaluating the probability of the event occurring anddescribing the magnitude of the consequences A discussion is then given

ade-of the measure undertaken to lower the probability ade-of occurrence or tomitigate the consequences and a "case" is made that the risk for theinstallation meets the ALARP safety criteria

In the North Sea this is often done with detailed quantified risk ments and the calculation of an overall IRR or risk of total loss of struc-ture Mitigation measures are incorporated until it can be shown that risk

assess-levels meet a minimum criteria and the cost of further mitigation has such

high cost to benefit ratios that further mitigation is no longer "practicable."

424 Design of GAS-HANDLING Systems and Facilities

These analyses tend to be rather long and complex and can negativelyimpact both project cycle time and cost Indeed, as a check to assure thatbasic known safety concepts are not inadvertently overlooked in the pile

of documentation which is necessary for a safety case, the safety caseapproach should include within it all the elements of the "API System,"Even if a safety case is performed, it is still necessary to assure compli-ance with good practices and that all elements of a proper safety manage-ment system are included Thus a common sense approach in the absence

of government regulation would be to use the API System for roostinstallations and, in those instances where there is a large concentration

of personnel or where abandoning the location may be impossible due toweather or remoteness, to use a qualitative safety case to think throughfire fighting and escape options