How to Design Instrumentation System in an Oil & Gas Industry?

What are the Design Basis Guidelines for an Oil & Gas Industrial Instrumentation Project 

Part-3

Instrumentation Specifications:

 

Field Transmitters:

All transmitters must be smart type operating on 4-20mA, 24V DC, 2-wire loop powered configuration, with analog signal superimposed with HART protocol.

Output Commands:

All output commands must be powered by 24V DC.

Signal Termination:

All electronic signals must terminate at the battery limit of the skid in separate Junction Boxes (JBs). Multi-pair cables must be used to connect these signals with DCS/ESD Marshalling in the Equipment room.

Feed Through Terminals:

Use "Wiedmuller" or equivalent feed through terminals in Marshalling cabinets.

Instrument Design:

 All instruments are designed for sweet gas service. No NACE compliance for MR 0175 is applicable.

Remote I/O Concept:

 No remote I/O concept is considered.

System Design:

 Separate systems with Marshallingcabinets will be used. Similarly, separate Junction boxes for ESD & DCS Systems will be designed.

Emergency & Fire Shutdown:

 In case of emergency & fire, all ESDV & BDV valves must operate with manual initiation by operator or automatically through combined control & ESD system for process shutdown etc. Shutdown activating devices (level, pressure, temperature) must be electric type. All ESDV & BDV must be provided with 24VDC solenoid coil for shutdown purpose.

Critical Control Panel:

 Critical Control Panel is being supplied for all Level Shutdown Button with Protection Hood. MOS enable switches and MOS Enable Pilot Light.

Instrument Air Supply:

 Instruments must operate on instrument air supply, which must be supplied through Instrument Air Header along the skid.

 Instrument Installation:

 Instruments must be installed on instrument stands where direct mounting is not possible.

Cabling:

 Underground/above-ground cabling must be used as per requirement. The above-ground cable must run through Cable tray/Ladder and conduit.

Zone-2 Hazardous Area:

 Use Exe JB’s (SS material-316) for cable termination in Zone-2 hazardous area.

Temperature Gauges:

 Temperature gauges must be bi-metallic every angle gauges for local indication.

Temperature Instruments:

 All temperature instruments must be provided with thermowells and must be 3 wire RTD, Pt100 & integral to the transmitter.

Fiber Optic Cable:

 Fiber optic cable must be single mode, multi-tube construction, loose fill, gel-filled, armoured cable as per ITU-T G.652. It must have resistance to pest attack, sandstorm and be impervious to sunlight.

Cable Signal Separation:

 

Fire and Gas, ESD and DCS signals must not be combined in the same multi-core cable.

Signal Separation:

 Following signals must not be combined in the same multi-core cable:

  • Analog inputs and outputs
  • Digital inputs and outputs
  • RTD
  • Thermocouple/mv
  • Machine Monitoring signals
  • Special signals such as pulse outputs.

Conductor Specifications:

 Stranded conductors must be annealed copper wire. The minimum size of instrument conductor must be:

  • 1.0 mm² for Analog & digital field signals and 
  • 2.5 mm² for SOV, Sirens and Beacons operation. 
  • Cabinet internal cables conductor must be a minimum 1.0 mm².

Cable Construction Standards:

 Construction of cable must be, in general, as per BS 5308 part-I.

Fire Resistant Cable:

 Fire resistant cable must have mica tape or other suitable material to meet the resistance criteria defined in IEC 331 & BS 6387.

Cable Screening Philosophy:

 Screening philosophy of cable must apply as following:

All single pair cables for Analog, RTD, Thermocouple, Digital (5 – 20 VDC) and low voltage signals (<5 VDC) must be provided with screen;

Multipair cables for Analog and digital (5-50 VDC) signals must have collective overall screen;

Multipair/multitriad cables for RTD analog Thermocouple & low voltage (<5 VDC) signals must have individual and collective overall screens.

Cable Armouring:

 Outdoor above-ground and underground cabling must be provided with steel wire armour (SWA). Indoor cables need not be provided with armor.

Flame Retardant Cable:

 Cable for normal application must be Flame Retardant per IEC 332-3 –C.

Fire Resistant Cable for Special Applications:

 Cable for ESD, Fire and Gas application must be Fire Resistant by IEC 331 and BS 6287.

Control Room Cable Entry:

 At control room cable entry, MCT frame and blocks must be used. The cable below the control room cabinets must be routed in cable trays.

Fiber Optic Cable Installation:

 Fiber optic cable must be laid in a separate trench from the pipeline. 

Underground Fiber Optic Cable Installation:

 Fiber optic cable must be laid underground in a 4” GI steel conduit. At all crossings e.g. roads and railways, cable must be laid in PVC pipe sub-ducted into GI pipe.

Fiber Optic Communication Equipment:

 Fiber optic communication equipment to be used for establishing communication of well pads to the centralized processing locations.

Zone-2 Cable Gland:

 Cable gland must be EEx(e) type for Zone-2 hazard.

Cable Gland Specifications:

 Cable glands must be made of brass nickel-plated, double compression type, IP66, metric thread (ISO), earth tag, lock nut, sealing washers and PCP shroud as per BS6121.

Junction Box Specifications:

 In general, the junction boxes must have the specifications like, Hazardous Class: EEx (e)

Enclosure Class: IP65, enclosure Material: Stainless Steel,  Terminal Block Color: Gray for signals, Green/Yellow for Screen Earth system.

Terminal block size suitable for wire size of 2.5mm² and screen earth 0.5mm². Gland plate thickness must be 2mm. Junction boxes must be provided with sufficient 2.5mm² terminals, end plates, stoppers and earthing terminals.

Cabinet Dimensions:

 Dimensions of the cabinet must be as per the manufacturer’s standard. However, the minimum size must be 1200mm W x 2000mm H x 800mm D, with 100mm including the plinth. Empty enclosures must be sourced from standard manufacturers like Rittal, Hoffman, Weidmuller, B-line, or equivalent.

Cabinet Features:

 The cabinet must have a bottom cable entry and a removable gland plate must be provided at the bottom for field cable entry with 20 % spare capacity.

Cabinet Material & IP Rating:

 The material of construction for control cabinets must be a minimum 2mm (14 or 16 gauge) sheet steel. The cabinet color must be RAL 7035. The complete enclosure must be of a minimum IP 54 design suitable for indoor installation.

Wiring Cross-Section:

 Connected wiring must have an adequate cross-section (not less than 0.2 mm²).

Spare Capacity:

 All Junction Boxes (JBs) and Cabinet must be designed with at least 25% spare terminals and also 25% spare space in addition to 20% installed I/O capacity.

Trunking/Wire Ways Capacity:

 Trunking/wire ways must have 40% spare capacity.

Cable Spare Capacity:

 All Junction Boxes (JBs) and multicore cables must have at least 25% spare capacity.

Mounting Heights:

 No equipment or terminal block/rail in the system cabinets must be mounted less than 400mm above the floor. No equipment or terminal block/rail in the marshaling cabinets must be mounted less than 200mm above the floor.

Terminal Spacing:

 A minimum of 50mm must be allowed between each terminal row and any plastic slotted.

Terminal Mounting:

 Terminals must be mounted on rails that are attached to a back pan/support and not directly to the surface of the enclosure.

Wiring Separation:

 Wiring of voltages greater than 24V (AC or DC) must be separated from instrument signal wiring.

ESD System Cabinet Reserve Space:

 ESD system cabinets in the DCS/ESD equipment room must have reserved space for at least two additional I/O racks.

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