100 System Design

AbstractThis section discusses the major phases of the design of instrumentation and control systems. It references other sections of the manual for detailed information on each aspect of the design process. It presents the overall picture of how the many components of an instrumentation design develop, from job scope to turnover to Operations.

Contents Page

110 Introduction 100-2120 Preliminary Design Considerations 100-2121 Getting Off on the Right Foot

122 Designing the Better Control System

123 Choosing a Control System

124 Evaluating Viable Alternatives

125 Life Cycle Costs130 Instrumentation Design Engineering 100-7131 Detailed Design Development

132 Design Specifications

133 Specification of Instrumentation

134 Documentation

135 Instrumentation Database140 Construction and Startup 100-10141 Documenting Field Changes

142 Commissioning

143 System Startup

144 Closing DocumentationChevron Corporation 100-1 July 1999

100 System Design Instrumentation and Control Manual110 IntroductionThe Instrumentation and Control Manual is intended to help engineers and designers design, construct, start up, and maintain typical Company instrumentation systems. It is intended to be used as a guide, with the understanding that no guide can replace sound engineering judgement.This section introduces the many aspects and procedures involved in designing an instrumentation system. Whether designing a small field job or a large facility, the elements of system design are similar.

Protecting People and the Environment is a cornerstone of how Chevron does busi-ness, and must become an integral part of the design of any Chevron facility.

With this commitment firmly in mind, a structured approach to defining, designing, and implementing a control system must be used to ensure success.

120 Preliminary Design Considerations

121 Getting Off on the Right FootFor the Control Systems Engineer, this first step is defining the objectives of the system he/she intends to install. This is a function embedded in the Chevron Project Development and Execution Process (CPDEP), and the analyses described below form an integral part of Chevrons Policy 530.

The Control Objectives Analysis (COA) is a facilitating process for defining what a control system does. The process consists of plant operators, process engineers, and control engineers reviewing plant process flow diagrams and defining the objective of each regulating device (control valve, damper, variable speed drive, etc.) on the drawing. The format of the objective is a single-sentence statement, defining what the regulating device always does to a process variable. (Example: CV-1002 main-tains overhead pressure between limits.)In the case of a new process on which plant engineers and operators do not have hands-on experience, the Control Objectives Analysis should be done with the assis-tance of engineers and operators from other facilities presently operating the process. Finally, experience operating similar processes should serve as a basis for the COA.

Similar facilitating processes define the objectives of safety shutdown systems (Shutdown Objectives Analysis, or SOA) and alarm systems (Alarm Objectives Analysis, or AOA).Only after these objectives have been defined and agreed to by Operations and Engineering, can the design of the control, safety, and alarm systems begin.July 1999 100-2 Chevron Corporation

Instrumentation and Control Manual 100 System Design122 Designing the Better Control SystemWith Objectives firmly in hand, the Control Systems Engineer needs to define the HOW of the control system.

Items which are defined in the Control Design Analysis process include:

System Geography - is control hardware in the field, in remote instrument enclosures or in a rack room in the control center? Will there be multiple sites where the operator can access the control system? Will multiple sites be peer or hierarchical?

System Architecture - what will be the defined and potential data transfer links to other control systems? To control and/or monitoring computers? To a Management Information system?

Control Architecture - how much of the control will be done by the systems front end? Will there be advanced control such as DMC? Will there be a sepa-rate computer for advanced control?

Environmental - what is the Area Classification for the plant and for field sites where controls will be located? For the area where operator interfaces will be located? What are the measurable airborne contaminants for these locations?

Operator Interface - does the operator see the process via a CRT, an array of controller faceplates, or field indicating controllers? Or via a combination of two or three of these methods?

Operability - can the process be manually controlled in the field using a manual bypass around the regulating valve? Will there be field operators to perform this function when required?

Reliability - what is the minimum acceptable operating factor for the control system? What is the economic incentive for increasing reliability by a defined percentage?

Failure Modes - what will be the status of the control system if individual instruments fail? Do all failures result in the control system going to (or tending to) the defined Fail-Safe condition of control valves and drives?

Expandability - if the control system intended for a mature, well-defined process with little potential for expansion, or is this a pioneering process or first step in a multiphase project?

Cutover Plans - for reinstrumentation projects, the plan for cutting over from existing to new instrumentation should be a part of the control design process.

Hot cutovers are typically more labor intensive than conversion en masse during a planned shutdown; however, most plants opt for the hot cutover, since it allows a more gradual conversion, and results in one less unknown during a plant startup.

Urban Renewal - the amount of re-engineering of existing facilities (reverifi-cation of the suitability of reused field instrumentation such as orifice plates Chevron Corporation 100-3 July 1999

100 System Design Instrumentation and Control Manualand control valves) needs to be determined at the initial design phase. This process is labor intensive if done properly - process conditions need to be field verified.

123 Choosing a Control SystemDigital technology now dominates the control hardware market. Electronic analog controls have all but vanished from the scene, and pneumatic controls are viable only in specialized applications where reliable electric power is not available, or where the Area Classification prevents installation of electronic controls without using elaborate cabinet or control room purging.

Note current environmental regulations in California virtually prohibit the exist-ence of Class 1 Division I areas.

Control & Operator InterfaceDigital electronic control should be considered as the default selection for all control systems installed in strategic facilities. With the exception of projects adding to existing control systems, solid justification must be given for deviating to elec-tronic analog or pneumatic controls.

Digital electronic control is available on a broad spectrum of platforms, from Single Loop Digital Controllers (SLDCs) through Programmable Logic Controllers (PLC) to multi-plant Distributed Control Systems (DCS).Note most SLDCs currently offered are in fact multi-loop digital controllers, with the capacity to control up to four valves from a 3-inch x 6-inch panel mounted face-plate.

Operator interfaces range from panel mounted faceplates (which emulate traditional panel-mounted controllers) to color CRTs using interactive graphics for display and control of operating parameters. The industry trend is toward the use of generic color CRTs running system-specific display and control software.

TransmittersSmart process variable transmitters should also be considered as the default stan-dard. These instruments offer higher accuracy and reliability than their electronic or pneumatic analog counterparts, and add the bonus of remote diagnostic data acquisi-tion and calibration checking.

Control ValvesSmart control valves are an emerging technology which offers extensive valve and process diagnostics, using the valve positioner - actuator as a sensor, or using pres-sure and temperature sensors embedded in the control valve body, or a combination of both. This technology should be considered on installations where maintenance access to control valves and drives is restricted.July 1999 100-4 Chevron Corporation

Instrumentation and Control Manual 100 System DesignField CommunicationsCommunications between Smart field instrumentation (transmitters and/or valves) and the control room are typically done over the same twisted pair of wires carrying the transmitter output or valve positioner input signal. Communications protocols range from vendor proprietary systems such as Honeywell DE- 6 Byte to multi-vendor open systems such as HART.

The Fieldbus communications protocol, which is being developed by an interna-tional consortium of instrument manufacturers, will offer the ability to link field instrumentation (transmitters, controllers, field indicators, valve positioners, and auxiliaries) on a multidrop power - communications wire pair. Control functions (algorithm execution) will be downloaded to the lowest possible tier of the system architecture, freeing up higher level computation capacity for running advanced control strategies.

Intrinsic SafetyIntrinsically Safe (I. S.) construction is intended to prevent sources of ignition (elec-tric sparks) in Hazardous Areas by limiting the transmission of power from non-Hazardous areas and by limiting the storage of energy in field devices.

Use of I.S. construction permits opening field enclosures (including transmitter and valve positioner housings) without first powering down circuits or sniffing the area to verify the absence of flammable mixtures.

There is no necessary correlation between I. S. construction and Hazardous Area Classification ratings nor between I. S. construction and Explosion-proof housing construction.

Because Intrinsically Safe construction severely limits the voltage and current which can be transmitted into Hazardous Areas, special attention must be given to limiting the number and type of field devices which cause voltage drops, and to the quality of field terminations. (Corrosion on field terminals can cause indeterminate voltage drops on current loops.)Final determination of whether this level of protection is appropriate for an installa-tion should be made only after an extensive review of local Electrical and Safety Codes.

The use of Smart field instrumentation, which permits communications from a non-Hazardous area, has diminished the use of Intrinsically Safe instrumentation systems in domestic petrochemical installations.

124 Evaluating Viable AlternativesOnce the scope and function of the control system is defined, the control systems engineer can focus on selecting hardware.

In all likelihood, more than one commercially available system will meet the requirements of the project. Consider the following factors in evaluating viable, competing systems:Chevron Corporation 100-5 July 1999

100 System Design Instrumentation and Control Manual System Integration - determine how well a system integrates:

horizontal integration, or the breadth of control hardware (regulatory and discrete control algorithms; continuous, batch, or state control operation) from a single manufacturer.

vertical integration, or the depth of control hardware (transmitters and valve positioners, controllers, network interfaces, operator consoles, advanced control computers, MIS links) and software to tie the pieces together.

Avoid the entanglements of multiple sources of interface software.

Uniformity - avoid putting one of everything in a control center. A strategic objective should be to have a single type of operator interface for all controls in a center; an absolute requirement should be a single operator interface for each group of plants under the control of a single board operator.

System Maturity - reject sunset technology unless youre fitting in the last piece of a multi-phase control replacement project. Recognize that even though a manufacturer is legally bound to provide spare parts support for a limited period of time following obsolescence of a product, he has limited control over keeping competent engineers in a support function on an obsolete system.

Product Stability - avoid the control system which appears to be in a constant state of evolution. (These are typically a maintenance nightmare.)

Technical Support - investigate the communications paths available for connecting plant support personnel to technical resources at the Factory. Consider also the level of local support you can expect, especially during the first years of system operation.

Configurability - evaluate the magnitude of the configuration task. A system requiring special-skills programmers for initial set-up will require these same specialists, a significant expense to the plant, for every future modification. By contrast, systems which configure with a higher level Operating System can be set up and modified by plant control or process engineers, maintenance techni-cians, or selected operators.

Track Record - past performance is a valid indicator of future actions. Be wary of born again control systems companies with a trail of dissatisfied clients but a promise that all is changed. Check out recent references on a potential vendors Happy Camper list; be prepared for candid dialog.

125 Life Cycle CostsThe quoted cost of a control system is the tip of a financial iceberg. Determine the Life Cycle cost of a system by reviewing the other cost components:

Training - engineers, maintenance technicians, trainers, and operators will all need training on a new system. Significant cost sub-components are tuition, time, travel, and frequency of refresher training courses.July 1999 100-6 Chevron Corporation

Instrumentation and Control Manual 100 System Design System Engineering - include an estimate of the cost of documentation, config-uration, and commissioning services.

Acceptance Testing - this procedure persists in a quality-conscious world. Determine where the system will be staged, how completely application soft-ware can be loaded, and how many User representatives will be needed to give the system a thorough Factory Acceptance Test.

Spare Parts - request a realistic list of recommended spare parts/components from the system vendor; advise him that the cost of these spares will be factored into the cost evaluation of the overall system. (The magnitude of the Recommended Spare Parts List increases once the basic system order is placed.)

Redocumentation - how readily does the system adapt to self-documentation for changes in field instrumentation, control strategy definition, or configura-tion? Does the system use a fill in the blanks configuration format, or does it require proficiency in a high-level computer language?

Maintenance - how much maintenance effort is required to keep the system in reliable operation? Can reliability be increased (and the cost of ownership decreased?) through minor adjustments to system architecture?

130 Instrumentation Design Engineering

131 Detailed Design DevelopmentDetailed design fleshes out the control system skeleton defined in the Preliminary Design phase of the Project. Successful installationsand thus successful projectsare rooted in the patient attention to an almost limitless number of details.

Designs Engineering ContractorsThe detailed design of a system is labor- and document-intensive. For this reason, detailed design work is frequently done by engineering contractors. They offer the advantage of being able to supply skilled technical personnel at short notice, and only for the duration of the project. The downside is that any technical expertise paid for by the Client and acquired by the contractor vanishes at the completion of the Project.Engineering contractors must be provided with current Chevron or plant Standards, Specifications, Drawings, and Forms, if the goals of Uniformity and Quality are to be realized.

Systems IntegratorsIn a similar fashion, systems integrators and packaged systems suppliers must be provided with Chevron or plant specifications stating minimum requirements for controls which they provide, integration with other systems, documentation and all other information normally supplied by vendors of non-packaged instrumentation.Chevron Corporation 100-7 July 1999

100 System Design Instrumentation and Control Manual132 Design SpecificationsDesign specifications are used to guide system designers. The application and the type of contract are important factors in determining the extent of design specifica-tion needed.

A typical design specification (Model Design and Construction Specification, Section J, Instrumentation and Controls) is available from the Projects and Engi-neering Technology Group (P&ET) of CRTC. This specification is modeled to allow for a number of options and is adaptable to fit specific jobs.The design phase of a job produces the construction specification, which usually comes in two parts: a written specification and a construction drawing package. These two parts fully define how an instrumentation system is supposed to be built.

Changes in specifications after a bid has been awarded can be very costly. It is therefore important to form an accurate bid package (specifications and drawings). Because an instrumentation system has many inter-related components, a thorough end-of-job review is recommended.

133 Specification of InstrumentationThe specification of individual instrumentation is usually done on ISA (Instrumen-tation Society of America) specification forms. These forms are widely used throughout the industry, and most contractors and vendors are familiar with them. These forms are found in ISA S20 which is included in Volume 2 of this manual. The ISA form is used during design and construction and startup and by the mainte-nance group after startup.

The ISA instrumentation specification forms include brief instructions for filling in the form. For additional guidance, this manual includes data sheet guides. Various sections of this manual also discuss instrumentation selection and specification.

Consult with the Monitoring and Controls Unit of CRTC for the latest information on computer generated ISA data sheets.

134 DocumentationA system designed in-house by Chevron, or designed by an engineering contractor, or designed and built by a system integrator/packaged systems supplier generally includes complete documentation for design, construction, operation and mainte-nance. These documents will usually satisfy the Federal and/or local safety and health legal compliance requirements for critical instrumentation.

The following should be considered as minimum documentation requirements for control systems installations:

Area Electrical Classification maps

Plot Plans & Elevations, showing location of and access to major equipment and critical instrumentation.July 1999 100-8 Chevron Corporation

Instrumentation and Control Manual 100 System Design Piping & Instrumentation Diagrams (P&IDs) - refer to Section 200. Process Flow Diagrams, showing flow rates and conditions of pressure, temper-

ature and chemical composition for all streams in the plant.

Process Control Diagrams, showing the configuration of front-end control strat-egies, as determined by the Control Objectives Analysis (COA), and verified by the Control Designs Analysis (CDA).

Advanced Control Strategy documents, including Control Narratives, describing Strategies for optimizing the Process. These would include complete DMC documentation.)

Logic Diagrams, defining the functionality of Safety Interlock Systems, as defined by the Safety Objectives Analysis.

Vessel Drawings, showing the elevation and orientation of nozzles and the maximum, normal, and minimum levels of product and/or interfaces within the vessel. (These are required for designing instrumentation bridles and ordering level instruments.)The vessel drawing shall also tabulate the following data for each level instru-ment connected to the vessel.

Type of instrument

Alarm setpoints

Specific gravity of process fluid(s)Specific gravity of seal or capillary fluid

Instrument span with calculations

Zero suppression or elevation

Instrument Data Sheets, describing the physical construction of the instrument hardware items procured for the project. (These Data Sheets must be complete enough to permit ordering instruments without additional descriptive documen-tation.)

Orifice Data Sheets, detailing flowing conditions for all orifice flowmeters. These data should be supplied by Process Engineers familiar with the plant of similar processes. Inaccurate process data will come back to haunt ALL engi-neering disciplines.

Loop Diagrams, showing the interconnections among all hardware specific components in a control loop.

Junction Box Wiring Diagrams, showing the layout of termination strips and their connection to Main or Branch cables or to field wiring.

Cable Schedules, listing the cables and pairs (or conductors) used for intercon-nection of instrumentation components. (In some cases, these may be combined with Junction Box drawings described above.)Chevron Corporation 100-9 July 1999

100 System Design Instrumentation and Control Manual Installation Details, showing the relative position of process connections, instruments, and Utilities (power, heat tracing, vents, drains, etc.), and listing the materials used for installation.

Configuration Forms, describing the software or firmware (or both) used for creating Control Strategies, Operator Displays, and Reports.

Critical Alarm, Instrumentation, & Emergency Shutdown testing programs (procedures and frequencies for testing).

Indexes, for cross-referencing all of the above.

Documentation may be developed and maintained using paper or electronic media, or a combination of both. In all instances, current documentation must be available to plant Operations, Maintenance, and Technical organizations.

Use of electronic documentation systems with relational data bases increases the speed and accuracy of the documentation effort, since a single data entry event generates (or edits) parameters on multiple, related data files.

Design ReviewsPeriodic reviews of project design documentation ensures that costly rework or reor-dering of material is eliminated. The frequency of these design reviews is best deter-mined by the Project Management team, to which the Control Engineer reports.

135 Instrumentation DatabaseThe efficient handling of the vast array of instrumentation information for a project is a key issue in any instrumentation design. It is desirable to create a Master instrumentation database. Data need only to be entered once and changes are auto-matically updated for all sub-databases.

Software tools are available to control instrumentation information and generate reports and schedules. An instrumentation schedule can be used to document most of the instrumentation information.

140 Construction and Startup

141 Documenting Field ChangesA well-planned and designed control project minimizes the number and nature of field engineering changes.

These field changes should be documented on a master markup set of Drawings maintained in the Project Engineering Office, and should include all necessary supporting documentation.

Field changes must be signed off by the same level of authority as original draw-ings or formal revisions thereto. Prior to issuing Field Change Orders, all appro-priate Management of Change (MOC) requirements must be satisfied.July 1999 100-10 Chevron Corporation

Instrumentation and Control Manual 100 System Design142 CommissioningThe commissioning process consists of verifying the proper installation, connec-tion, and calibration of all instrumentation items on the Project.Specification ICM-MS-1586, Instrument Commissioning, is a guide for preparing newly installed instrumentation prior to plant startup. It describes the contractors responsibility for inspecting, checking, adjusting, and calibrating the instrumenta-tion and documenting all of the work for approval by the Company.

Recent trends in instrumentation have eased the burden of the Commissioning process:

Most Smart process transmitters can be interrogated from the control console or from termination panels in the rack room, to verify that the right trans-mitter is connected to the right terminations. (Forcing the transmitter to iden-tify itself by Tag Number is a technique for electronically ringing out a transmitter installation.)

The accuracy of digital electronic transmitters far exceeds that of field test equipment, and digital transmitters show no tendency to drift. Therefore, shop or field calibration of transmitters becomes superfluous. Instruments can move directly from the Tally Room to the installation site.

The increasing use of Smart valve actuators or positioners permits calibration checks and recalibration of control valves from the rack room or marshaling panel. This minimizes the requirement for cycling control valves through the valve or instrument shop prior to installation.

All instrument installations should be signed off by the installer, the instrument inspector, and an Operator. OSHA regulations (29 CFR 1910) require that Critical instrumentation be installed and inspected by qualified workers.

143 System StartupAt the system startup phase, operation of final control elements is switched over to the new control system.

A major effort is required to tune control loops, especially on a grass-roots project, or loops on a reinstrumentation project which did not previously exist.Prior to attempting to tune control loops, verify that any control configurations which inhibit controller response on changes in set point have been disabled. (These features will need to be re-enabled following controller tuning.)The use of a high speed data recorder (with chart speed selectable up to 6 in. / min.) will aid in the capture of process response to changes in set point or changes in controller tuning constants. Use of high speed trending on a CRT display is accept-able, especially if the set point, process variable, and controller output can be trended on the same display.Chevron Corporation 100-11 July 1999

100 System Design Instrumentation and Control ManualA moderate amount of process variable damping is required for flow loops on digital controllers, to prevent the control algorithm from chasing noise on the PV signal. (The magnitude of this noise is not apparent on analog instrumentation, due to the inherent damping of inputs from volumetric capacity (pneumatic controls) or input R-C filters (electronic analog controls).When tuning Cascade Controllers, tune the slave controller first, then the master controller.

At the conclusion of controller tuning, note tuning constants in a secure logbook, which can be used for future reference to determine is controller tuning constants have been altered.

144 Closing DocumentationAll field changes must be transferred to permanent documentation following turn-over of the control system to the Proprietor of the project.Final, As-Built drawing revisions must be provided to plant Operations, Mainte-nance, and Engineering offices as part of the projects documentation. In addition to the documentation described on Section 134, this final documentation project must include operating instructions, maintenance manuals, and spare parts lists for all equipment installed.July 1999 100-12 Chevron Corporation

Manual Contents100 Contents110 Introduction120 Preliminary Design Considerations121 Getting Off on the Right Foot122 Designing the Better Control System123 Choosing a Control System124 Evaluating Viable Alternatives125 Life Cycle Costs

130 Instrumentation Design Engineering131 Detailed Design Development132 Design Specifications133 Specification of Instrumentation134 Documentation135 Instrumentation Database

140 Construction and Startup141 Documenting Field Changes142 Commissioning143 System Startup144 Closing Documentation

Engineering SpecificationsStandard Drawings & Forms