Table of Contents
1. General Design Basis
2. Units of Measurement, Scales, Charts, and Nameplates
3. Measurements
4. Centralized Controls
5. Instrument Piping and Connections
6. Instrument Field Installation
7. Heat Tracing, Sealing and Purging
8. Power Supply, Alarm and Shutdown Systems
9. Control Valves
10. Safety and Relief Valves
11. Reference Specifications and Standards
12. Typical Drawings
Symbol explanation
(*) Feature Required
(o) Feature Not Required or Applicable
(x) To Be Specified by Detailed Engineering Contractor
1. General Design Basis
1.1 Scope
1.1.1 This specification covers the requirements for basic design, selection, testing, inspection and installation of instrument equipment.
Only generally significant features are included.
1.1.2 The guidelines established in this specification and the specification and standards mentioned herein are considered to be minimum requirements.
All instrumentation shall conform to good engineering practice and procedures.
1.1.3 Instrumentation will be shown on appropriate engineering flow diagrams. The symbols used will be in accordance with (*) ISA S5.1 & S5.3.
1.1.4 All instrumentation shall be specified on the instrument schedule.
1.1.5 For instrumentation supplied as part of package units refer to the “engineering and design specificartion for package units”.
1.1.6 Electrical instrumentation, installation, materials and area classification shall be in accordance with local codes and other standards, agreed for the project.
1.2 Basic Instrument Selection
1.2.1 The main instrument control system will be:
| (o)
|
Pneumatic
|
| (o)
|
Electronic (Analog)
|
| (*)
|
Electronic (Digital) control system
|
| (o)
|
Distributed using sattelite station (s)
|
| (*)
|
Centralized in the control building (s)
|
| (o)
|
1.2.2 Local control loops shall be:
| (*)
|
Integrated with the main instrumentation system
|
| (o)
|
Pneumatic
|
| (o)
|
1.2.3 Transmission of analog measurement and control signals will be:
For pneumatic instrumentation:
(*) 0.2 - 1 bar g
(o) 0.2 - 1 kg/cm2g
For electronic instrumentation:
(*) 4 - 20 mA (two wirte system)
(o)
1.3 Instrumentation Protection
1.3.1 Electrical Protection
All electronic instrumentation located in hazardous areas shall be designed and installed in accordance with the approved area classification drawings.
Applicable standards are:
| Cenels
|
Others
|
||||
| General
|
(*)
|
EN 50 014
|
(o)
|
||
| Flameproof
|
(Eex-d)
|
(*)
|
EN 50 018
|
(o)
|
|
| Intrinsic safe
|
(Eex-i)
|
(*)
|
EN 50 020
|
(o)
|
|
| Increased safety
|
(Eex-e)
|
(*)
|
EN 50 019
|
(o)
|
|
| Pressurized
|
(Eex-p)
|
(*)
|
EN 50 016
|
(o)
|
|
| Nonsparking
|
(Ex-dn
|
(*)
|
(x)
|
per local
|
|
| standards
|
|||||
The following philosophy is adopted:
| (*)
|
All instrumentation as far as possible in non hazardous and zone 2 areas: Ex-n, Zone 1 areas: Ex-d
|
| (o)
|
All instruments as far as possible Ex-i
|
| (o)
|
1.3.2 Environmental Protection
Instrument enclosures for outside installation shall be in accordance with:
(*) IP-55
(o)
2. Units of Measurement, Scales, Charts, and Nameplates
2.1 Units of Measurement
Units of measurement shall conform to the following list unless otherwise specified:
| Flow
|
-
|
Liquid
|
kg/hr
|
(kilograms per hour)
|
| Flow
|
-
|
Steam
|
kg/hr
|
(kilograms per hour)
|
| Flow
|
-
|
Gas
|
kg/hr
|
(kilograms per hour)
|
| Level
|
%
|
(percent of range)
|
||
| Pressure
|
-
|
Gauge
|
bar g
|
(100 kPa gauge)
|
| Pressure
|
-
|
Absolute
|
bar a
|
(100 kPa)
|
| Pressure
|
-
|
Compound
|
-1-0-
|
bar g (100 kPa gauge)
|
| Temperature
|
-
|
°C
|
(Degrees centigrade)
|
|
| Analyzers
|
-
|
Determined per individual
|
||
| application.
|
||||
| Viscosity
|
mPa.s (sP)
|
|||
| Density
|
kg/m3
|
|||
| Velocity
|
m/s
|
2.2 Graduation
Graduation of indicating scales shall be as follows:
| Oriffice meters
|
:
|
0-10 square root
|
| Rotameters
|
:
|
0-100 uniform
|
| Pressure
|
:
|
direct reading
|
| Level
|
:
|
0-100% uniform
|
| Temperature
|
:
|
direct reading
|
Appropriate chart and/or scale factor will be shown on integral name-plates.
Reading on the digital control system are as follows:
| Flow meters
|
:
|
direct reading, linearized
|
| Pressure
|
:
|
direct reading
|
| Level
|
:
|
0-100 uniform
|
| Temperature
|
:
|
direct reading
|
| Analyzers
|
:
|
direct reading
|
2.3 Metrological Data
| -
|
Design Rainfall Intensity
|
:
|
6.35 cm/h
|
| -
|
Design Dry bulb temperature
|
:
|
|
| -
|
Minimum
|
:
|
-20°C
|
| -
|
Maximum
|
:
|
38°C
|
2.4 Nameplates
Nameplates shall be in the English language.
Instrument nameplates on the panel shall read instrument tagnumber, service and chart/scale factor.
Instrument nameplates on back of panel and field mounted instruments or Instruments components shall read the instrument tagnumbers only.
3. Measurements
3.1 General
The range of transmitters, controllers and indicators shall be selected such that the operating condition will be in the middle third of the scale where practicable.
Blind flow transmitters forming part of a control loop will have a receiver gauge connected to the output of the transmitter. The receiver gauge will be located such that it is readable from the control valve.
3.2 Flow Instruments
Flow instruments in general shall use:
(*) Orifice flow meters
(o) Vortex flow meters
(o)
Where this method is not satisfactory other devices may be used, such as integral oriffice meters, Pitot tubes, Venturi tubes, positive displacement meters, etc.
Glass tube rotameters shall only be used for nonhazardous services (low pressure air, nitrogen, water, etc.).
3.2.1 Orifice Flow Meters, Flow Nozzles and Venturi Tubes
Orifice,fFlow nozzles and Venturi shall be designed in accordance with
(*) ISO 5167, latest edition.
The primary element calculation shall be made available (normally, flange taps shall be used).
The ratio of the orifice bore to inside pipe diameter (B=d/D) shall be between the limits as alid down by ISO 5167.
If d/D ratio exceeds 0.75 for a 5000 mm H2O differential range, the process line shall be increased for the meter run.
Normal flow shall be approximately 70% of maximum flow meter capacity, which is rounded-off to give a suitable multiplying factor.
If static pressure measurement for pressure compensation is required for a compressible fluid, it is taken upstream of the measuring element.
3.2.2 Design of Oriffice Meter Runs and Venturi Tubes
(Refer to Sketch 12.1). The design of oriffice meter runs shall be in accordance with
(*) ISO 5167
(o)
Oriffice flanges shell be per
(*) ANSI B16.36 and the following:
(o)
a. Flanges shall be welding neck type.
b. The raised face of raised face flanges shall not be less than 0.06 in (1.6 mm).
c. Pressure taps shall be equipped with butt welded connections, screwed, seal welded connections are not allowed.
3.2.3 Piping Requirements for Meter Run
Minimum straight piping upstream and down stream of orifice shall be minimum as specified in
(*)ISO 5167
(o)
Straightening vanes will not be used. Straigh runs for other flow meters types will be as per manufactuere’s instructions.
For lines sizes smaller than 2 inch orifice plates will be installed in special prefabriceted meter runs. In this case the purchaser will provide further details.
3.2.4 Orifice Tap Orientation
An orifice assembly shall be positioned with pressure connections located as shown in the typical details. The same rule for orientation of pressure connections applies for corner taps. Orientation of other types of taps shall be agreed per individual case.
3.2.5 Flow Transmitters
Standard differential pressure ranges for flow transmitters:
| (*)
|
0-250
|
mm H2O
|
(*)
|
0-2500
|
mm H2O
|
| (*)
|
0-500
|
mm H2O
|
(*)
|
0-5000
|
mm H2O
|
| (*)
|
0-1250
|
mm H2O
|
Instrument spans lower than 250 H2O are not preffered.
3.2.6 Alternative Type Flow Meters
For fluids containing solids the following flow meter shall be considered:
a. Magic flow meters, for liquid service where the fluid is conductive.
b. Wedge type flow elements. In this case the transmitters shall be equiped with double diaphragm capillary seals, flush mounted to the flow element.
If these elements are installed in a horizontal lines, it shall be installed in the same plane as the process line to avoid accumulation of dirt.
For custody transfer measurements the following flow elements should also be considered:
a. Magnetic flow meters
b. Turbine flow meters
c. Vortex flow meters
d. Positive displacement meters.
3.3 Level Instruments
For general applications the following types will be used:
- Standard differential type transmitters (“dp cell”)
Where impractical, other principles may be used.
In general gauge glasses will be provided which cover the range of the level transmitters.
3.3.1 Differential Type Level Measurements
Reference Connections.
Wet reference legs will occur where the condensable process fluid temperature is always higher than the maximum ambient temperature.
Dry reference legs will occur when the vapour pressure is lower than the working pressure. Generally, where the process fluid temperature is always lower than the minimum ambient temperature.
For other cases, where condensable fluids are involved, i.e. the process fluid temperature within minimum and maximum ambient temperature, the reference shall be either electrically traced or instruments with double diaphragm seal and capillaries shall be used.
Maximum capillary length shall not exceed 2 x 3 meters.
3.3.2 Diaphragm Seals
For corrosive services, or when (suspended) solids are present in the process fluid, flange type (minimum 3” ANSI 33 lbs RF) transmitters or double diaphragm type and capillaries shall be considered (see also clause 5.1).
Flange type or diaphragm seal type instruments shall use drip rings as indicated on the typical details.
3.3.3 Displacer Type Instruments
External displacer type level instruments are preffered for ranges up to 1524 mm (60 inch).
Where impracticable due to solidification, viscous service, or severe level fluctuations (due to boiling) other measurement principles will be applied.
Displacer type level instruments will have a rotatable head.
Internal displacer level instrument with stilling tubes will only be used in special cases.
The internal type shall not be used in vessels with spargers.
For installation see typical details.
3.3.4 Float Switches
Ball float actuated switches may be used only for alarm applications on lube oil tanks.
3.3.5 Tank Level Indicators
Float and external scale (board) type level instruments will be used for open tanks of moderate height and where precise level indication is not required.
Servomotor driven displacement type level instruments will be used for accurate measurements and for level measurements and for level measurements in pressure vessels and spheres.
3.3.6 Gauge Glasses
Gauge glasses shall be reflex type for all services except the following, where through-vision type will be used:
- Interface between two liquid
- Viscous fluids or fluids containing gum or sediment.
- Liquids requiring protecting shields.
- C3 and lighter hydrocarbons.
Protective shields shall be used on gauge glasses if the liquid will attack glass, e.g. in steam condensate ands caustic services.
Frost shields shall be used if the operating temperature is below 0°C.
The four section size (glass size no.9) will be the maximum normally used. Where more than four glasses are necesarry to cover the full range, multiple gauges shall be used.
Gauge glasses will not be illuminated.
Large number gauge glasses will be used for cold services with liquids that boil at ambient temperature. Tubular type gauge glasses shall not be used. For installation of gauge glasses see typical details.
For hazardous services double window type or magnetic type shall be considered. All level gauge types shall be welded, flanged design.
Screwed/seal welded construction is not acceptable.
3.3.7 Mounting of Level Instruments
Level instruments shall be mounted externally to the vessel with valved connections.
3.3.8 Standpipes Design
Standpipes will be applied for following cases:
- Where a concentration of several level instruments around a standpipe will provide a better piping hook-up.
- On horizontal drums, where top and bottom vessel connections are required to obtain visibility of the complete vessel.
Standpipes will be 3 inch, they will not be separated from the vessel by block valves. Vessel connections will be 2 inch.
3.4 Pressure Instruments
Measuring elements in general will be Bourdon tubes, bellows or diaphragm elements. Other measuring principles may be utilized.
Measuring element material will be ANSI 316 stainless steel, except where process conditions require other materials. Pressure instruments shall have overrange protection to the maximum operating pressure to avoid a shift in calibration. Instruments which can be exposed to vacuum shall have underrage protection. For viscous or corrosive services diaphragm seals will be used.
3.4.1 Pressure Transmitters and Pressure Switches
Blind pressure transmitters shall have a pressure gauge connected to the process line or same pressure tapping.
Pressure switches for pneumatic signals shall preferably have brass bellow measuring elements.
Connection shall be NPT female preferably 1/4 inch.
3.4.2 Pressure Gauges
1. Local Process Indicators
Pressure Gauges will conform to ANSI B 40.1 grade A accuracy 1% of full range.
On pulsating services glycerine filled gauges will be used if available, otherwise pulsation dampers shall be installed.
Nominal dial size shall be 100 mm.
Stainless steel case with blow-out protection will be used.
Red markings at safety valve relief pressure are required for applications as outlined in local safety codes.
2. Pneumatic signal receiver gauges
The requirements for pressure elements shall be identical to process gauges except:
- Pressure elements shall be phosphor bronze.
- Connection shall be 1/4 inch NPT male.
Scale graduations over 0.2 - 1.0 bar g range shall be consistent with graduations as given in paragraph 2.2.
3.5 Temperature Instruments
Thermocouples are normally used for remote indication are recording.
Thermocouple EMF is generally measured by nul-balance (potentiometric) or electronic feed-back circuits. For high accuracy, narrow span and application upto 500°C, resistance elements, Pt 100 ohm may be utilized.
Transmission of electric temperature measurement signals will be:
4÷20 mADC (two wire system) using head mounted transmitters for control and shutdown signals.
Temperature indication only, within the DCS system, will use multiplexers.
All temperature sensing devices shall have a nominal outer diameter of 6.0 ± 0.1 mm be installed in protecting sockets or thermowells with a bore of 6.5 mm, drilled from solid stainless stell or other material as determinated by corrosive conditions.
Carbon steel shall not be used.
For installation of thermowells refer to typical details.
3.5.1 Thermocouple Instrument
1. Thermocouples
Thermocouple elements will be chromel-alumel (type K) for temperatures from 500°C to 1100°C and for skin-point measurement.
Temperature/EMF curves shall be in accordance with the latest ANSI standards. Thermocouple elements shall be of the mineral insulated metal sheathed execution with insulated tip, unless otherwise indicated. Thermocouple heads will be cast iron, zinc plated. Heads shall be fitted with screw covers with retaining chain.
2. Resistance Elements
Resistance elements shall be of the vibration resistance type.
For field wiring a 4-wire system shall be provided.
Depending on the actual selected instrumentation a 3-wire or a 4-wire configuration will be selected. Heads for resistance elements will have the same basic design as those for thermocouples.
3. Thermocouples Extension Wire
Temperature/EMF curves, general construction and colour coding shall be as per latest ANSI standards. Thermocouple extension cable for chromel-alumel couples will be copper-constantan with matching characeristics.
3.5.2 Local Indicators
For local indication, dial thermometers with Bi-metal actuators shall be used. Local indicators shall be heavy duty, industrial type.
Nominal dial size shall be 100 mm. Case to be stainless steel, weatherproof construction (IP 55).
Case to have back connection with adjustable gland to permit horizontal and vertical adjustment of the indicator in the well and rotation of dial.
3.6 Analyzers
Analyzers systems shall be in accordance with design requirements applicable for the project.
Fast loop circuit shall be calculated for the application involved considering the speed of response required under actual prcess conditions and location of the analyzers/sample take-off points.
Delicate/complex analyzers will be centralized in prefabricated analyzer houses.
Simple analyzers (e.g. pH, conductivity redox, etc.) will be installed “on line”.
4. Centralized Controls
The engineering flow digrams will indicate which instruments are located in conditioned enclosed spaces as, the control room, auxiliary room or sattelite house(s).
No hydrocarbons, chemicals or other process fluids shall enter these conditioned enclosed spaces, nor local panels containing electrical instruments.
The enviromental conditions for process measurement and control system shall comply with ISA-S71.04 by latest edition.
4.1 Transmission Signals
4.1.1 Routing
Routing of cables will be selected to minimize possible damage to the cables due to contamination or fire hazard.
Cabling between the instrument and the junction box shall be supported by open tray or open conduit.
The field junction box will in general be located in the unit.
Multicore cabling between the field junction box and the main control room will be rounted underground.
Signal cables, in general, will be laid together in common trenches or trays for instrument signal lines. Refer to typical layout sketch.
Trenches will be kept away from power cables, transformers and electric motors whenever possible.
The distance of instrument cable trenches relative to power cables will be 0.6 m minimum when run in parallel. Segregation of instrument cables in trenches will be executed per typical drawing. Multicore cables will be used to the maximum possible extend.
High and low voltages will not be combined in one multicore cable.
In general, spare wires in multicore cables will be connected to terminals.
Cabling shall include for approximately 20% overall spares.
4.1.2 Pneumatic Signals
Pneumatic signals will be transmitters via 6 mm OD annealed single copper tubing.
4.1.3 Electric Signals
Electric signals will be transmitted via cables with stranded 0.5 mm2 or 0.8 mm OD conductors, with polyvinyl insulation, and armoring consisting of steel wire, steel wire, steel braid or steel taps.
T/C signals will be transmitted via solid 1.2 mm OD conductors, with polyvinyl insulation.
Multicore cables will be steel wire armored with PVC outer jacket, suitable for underground installation.
Conductors will be stranded 0.5 sq.mm for electronic signals and solid 0.8 mm OD for the T/C signals.
Conductor size for power supply cable will be as required by the load of the individual user.
Electric signal cables will be twisted a 5 cm lay and be provided with an overall mylar tape screen.
T/C cables and digital pulse cables will be twisted and be provided with mylar tape screen, per individual signal.
Date highways will use coaxial tables, specifications as per vendors recommendation.
4.2 Control Center
The centralized measurement and control system will be located in this center. The operator interface will concentrated on the operator console(s) and systems cabinets housing the in/outputs, function hardware/software are normally located in an auxiliary room.
4.2.1 Operator Console
The operator console shall present all relevant information and control facilities for the operator’s particular area of responsibility.
These basic functions shall provide:
- Indication of control and noncontrol variables
- Manipulation of control loops, including set point, mode and output
- Alarm annunciation and display
- Process variable, tabular log display
- Pulsating alarm outputs to drive hard wired alarm lamps having external lamp test button
- Start/Stop pushbutton station motor operation
- Shut down functions
- Customs Displays
4.2.2 Auxiliary Room
The equipment installed in the auxiliary room such as alarm, relay systems, power supply and distribution systems, includes process interface cabinets and controller cabinets. These are connected through a redundant data hiway branch to the operator console in the control room.
Where feasible multicore cables will terminate in the auxiliary room on rearrangement boards for easy distribution of signals in the control center.
4.3 Local Panels and Junction Boxes
4.3.1 General
Local panels, where specified shall take into account protective requirements for weatherproofing and hazardous areas.
Local panels that only contain signal lights and/or pushbuttons and electric switches may use standard junction boxes (Eex-e design).
Local panels containing other instrument equipment will be specifically designed such equipment and shall be constructed from sheet steel which is at least 3 mm thick.
All local panels will be suitably protected for use outdoors in a potentially corrosive atmosphere.
Process fluids, including water, seal tube and lube oil shall not be piped into local panel units containing electrical circuitry.
Panels shall be installed complete with all equipment and accessories for system operation, and fully wired.
4.3.2 Accesibility
Panel design shall permit satisfactory access to all components, instruments, terminal boxes, etc., for operational and maintenance procedures but nevertheless comply with area classification requirements.
4.3.3 Wiring and Tubing
Terminal inside local panels/junction boxes shall be of screwed type. No more than one (1) conductor may be connected to one side of a terminal. Jumper bars shall be used when two or more terminals have to be interconnected.
All wire and tubing terminations shall be properly identified and tagged both on the wiring and at terminal blocks, or on the tubing and at the bulkheads.
All cabling shall enter at the bottom of the junction boxes.
4.3.4 Segregation
Instrument signal wiring and cabling shall not be shared with power supply cabling in the same junction box.
To permit easy routing of field cabling and control/auxiliary room interconnecting cabling between the various systems, a false floor will be considered. The minimum distance, for access, between cabinets shall be 700 mm, or as required by local codes.
Panel and cabinet shall include for approximately 10% overall spare space.
4.4 Grounding and Screening
4.4.1 Grounding
There are two distinctly different grounding systems:
- Control systems dedicated signal ground in the control center
- General (electric) safety ground.
.1 The basic priciple of the control systems dedicated ground is that isolated ground bars are provided in all control systems cabinets and that these are in a “star” configuration connected to the dedicated (clean) signal ground provided in the control center.
.2 The general (electric) safety ground system shall be used to positively ground all metal cabinet structures, junction boxes and metal cable armouring.
4.4.2 Screening
A consistent priciple of interconnection of the cable screens is of paramount importance to minimize interference.
The basic priciple is to have screens isolated at instrument/field junction box and interconnected at the control center only to the dedicated signal ground.
5. Instrument Piping and Connections
5.1 Instrument Process Piping
Instrument piping up to and including the first block valve and in line instrument equipment shall confirm to the line class or vessel rating concerned.
The first block valve will be installed as close as possible to the process tapping. Unions between the process tapping and the first block valve are not permitted.
Instrument piping after the first block valve may use alternante materials or type of connections, but selection will be made considering the line class concerned.
All process connections shall be flanged, with a screwwd connection at the transmitter only. Bends will be used instead of elbows, where practical.
5.1.1 Tubing
Seamless carbon steel, soft annealed or type ANSI 316 of European equivalent stainless steel where required.
Tubing shall be 12 mm OD x 10 mm ID, sample lines for analyzers may be executed in 6 mm OD x 4 mm ID.
5.1.2 Fittings
Carbon steel or stainless steel tube fittings, compression type.
5.1.3 Valves 1/2 Inch and Smaller
Forged carbon steel of forged AISI 316 stainless steel, barstock, union gland.
Connections to be compression type, suitable for tubing as selected. (Only to be used after the first block valve).
5.1.4 Manifold Blocks for Transmitters
Manifold block design shall allow close coupled mounting on the transmitter with the following characteristics:
| Service | Type |
| Flow | Block/equalizing valves and drain/vent valve (4 or 5 valve manifold) |
| Pressure | Block, drain/vent valves (2 valve manifold) |
| Diff. pressure and level equalizing valve | Block, drain/vent valves (4 valve manifold), no equalizing valve |
5.2 Instrument Connections
5.2.1 Instrument Connections on Piping
For instrument connections on piping refer to table per paragraph 12.2.1.
5.2.2 Instrument Connections on Vessels
For instrument connections on vessels refer to table per paragraph 12.2.2.
5.3 Instrument Air Piping
Piping material for instrument main and branch air headers shall conform to the pipe specification.
Take-off shall be made from the top of the header.
Spare take-offs without block valves will be provided.
Instrument air supply piping to the local individual users will be 6 mm OD x 4 mm ID, annealed copper tubing. Each user will be provided with an airset with indicator.
Instrument air supply to centralized controls will be as required by the specific system configuration.
Instrument air distribution system shall have block valves at the following points:
5.3.1 At each take-off from main or branch header.
5.3.2 At each user.
6. Instrument Field Installation
6.1 Mounting of Field Instruments
Transmitters and local controllers will be mounted on 2 inch pipe stands where practical.
Flow and pressure transmitters will generally be line mounted, supported from the process line, to keep the impulse lines short.
Delicate instruments will be protected against adverse weather conditions.
Where centralization of local instruments is required to facilitate local operation of (packaged) equipment, simple open rack type panels will be used. Delicate instruments, however, will be housed in closed cubicle type local panels.
6.2 Mounting of Analyzers
Simple analyzers such as pH, conductivity etc. will be installed on line. More complicated analyzers (e.g. chromatographs) will be installed in local sheds or in artificially ventilated analyzer buildings.
6.3 Accesibility of Instruments
The requirements for the accesibility of field instruments and block valves are specified in the “general design specification for accesibility of instrument connections”, BN-SP-K2.
7. Heat Tracing, Sealing and Purging
7.1 Heat Tracing
Heat tracing will be foressen when the high pour on freezing point of liquids or condensed vapour would render an instrument inaccurate or inoperative.
Instruments are to be heat traced separately from the main process tracing, except pressure gauges which may be protected by the pipe line or equipment tracer.
Isolators, allowing heat to tracing system of instruments will be grouped as much as possible.
Each isolator will be tagged with the instrument tag number. Heat traced instruments will be provided with protective isulation cover.
Heat traced lines will be insulated. Instruments and lines containing liquid which would tend to boil due to heat tracing, shall be separated from direct contact of the heat tracer by means of spacers.
7.2 Sealing
Sealing will be foressen when heat tracing is not possible or not economical, such as in case of:
- Extremely high viscosity
- Solidification at zero flow
- Different liquid phases in the process fluid
- When entrapping vapour may occur in the meter piping due to overheating
Sealing shall be avoided on flow instruments.
7.3 Purging
Purging will be foressen when heat tracing and sealing are not possible, such as in case of:
- To prevent plugging of instrument and instrument piping when polymerization may occur
- To avoid damage to the instrument by corrosive liquid and or gasses
- When solids are present in process liquids.
A check valve will be installed in all instrument purge applications, provided by the instrument department.
Purge flow will be reguleted to ensure a sufficient low flow, to insure that there is no pressure drop fluctuation effecting the read-out.
8. Power Supply, Alarm and Shutdown Systems
General design requirements for power supply, alarm and shutdown systems shall be according general specification BN-SP-K4/ BN-SP-K5.
8.1 Power Supply
The power supply and distribution system will be as shown on the typical drawing. Each feeder panel will have its own fuse to protect the phase, and an isolating switch in both phase and neutral.
8.2 Alarm
The annunciator system will be:
(o) Dedicated annunciator system(s)
(o) Integrated in the shutdown system
(*) Integrated in the main control system
(o)
Alarm system shall be fail safe, utilizing normally closed alarm contacts, which open on fault.
Where one “off normal” signal causes a chain reaction of “off normal” signals in an interrelated alarm system (for example compressor systems), only the first alarm shall give a visual and audible alarm.
An acknowledge button and (lamp) test switch will be provided for each operating station.
Alarm signals will generally be actuated from the control loop transmission signal except when vital (safety) for the process or when no transmission signal is available, in which case direct measuring switching devices will be used. Vital process alarm will have separate process tappings and separate activating deviced.
8.3 Shutdown System
The shutdown/interlock system will be:
(*) Segregated from the main control system
(o) Shutdown interlocks segregated from sequential controls included in the main control system
(o)
(x) Relay type
(x) Solid state type
(x) Ferrite core type
(o) PLC type
(*) Installed in the auxiliary room of the control center.
The following shutdown signals will be obtained from dedicated transmitters and take-off points which are independent from the control loop, unless when actuation from the control loop transmission signal is justified.
This main be acceptable in case of clean, none corrosive services, system selection criteria will be considered:
a. System complexity
b. System reliability
c. Process safety requirements
d. Space requirements
e. Maintenance aspects and spare parts
f. Price
Shutdown and safety interlock system will be fail safe and have solenoid operated emergency devices energized under normal conditions.
Shutdown actions will be displayed by an alarm signal obtained from the monitor switch (DPDT contacts).
These monitor switches will be installed in 19 inch racks located in system cabinets.
The system cabinets are generally installed inside the auxiliary room of the control center.
8.4 Radio Frequency Interference (RFI)
Electrical/electronic equipment for shutdown applications shall conform with the requirement of: SAMA Standard PMC 33.1, latest edition.
- Electromagnetic susceptibility of process control instrumentation.
Such equipment shall be RFI immune to this standard, class 2 (10 V/m), bands a, b and c (10-1000 Mhz). The output shall not deviate more than 0.1% span.
9. Control Valves
9.1 General
9.1.1 Diaphragm Operated Valves
Control valves shall generally be diaphragm motor operated type, air actuated with flow characteristics to suit application.
Valve body material shalll be in accordance with the piping classification.
Trim material will be stainless steel for normal applications. Control valves in throtting services will generally have solid-V-port cage type trims.
Hard-facing trim materials will be used for differential pressure above 10 bar, all steam applications for erosive services and where cavitation and flashing may occur.
The extend of hard-facing will be as specified in BN-SP-K6. Control valves with process temperature in excess of 250°C require radiating fins. For process temperatures below 0°C, extension-bonnets shall be provided.
Valves in which considerable expansion takes place, or substantial quantities of liquid flash to vapor, shall have a body one size larger than the trim.
9.1.2 Butterfly Valves
Butterfly valves shall be heavy duty design with powerful (piston) operators to permit precise positioning of vane.
9.1.3 Special Valves
For unusual applications control valves with Saunders patent body, split-body, angle-body, etc., may be used.
9.1.4 Application of Positioners or Boosters
Pneumatic valve positioners shall be used based on process or mechanical conditions as follows:
| Flow control | no positioners, but use a booster when required to increase response time |
| Level control | use positioners in all cases |
| Pressure control | use positioners for all gas and vapor service and boosters for liquid pressure when required to increase response time |
| Temperature control | use positioners in all cases |
9.2 Calculations
Control valves shall be sized for the available pressure drop at normal flow (refer BN-K070, design data - general), but based on a flowing quantity equal to normal flow times an oversizing factor of 1.8.
The calculation will be checked for maximum flow with an oversizing factor of 1.1.
The system friction loss (including other dynamic losses), excluding the control valve pressure drop, shall not exceed 2/3 of the control valve pressure drop in the wide open position.
Control valve oversizing factor normal flow conditions will be as follows:
| System Friction Loss
|
Oversizing
|
|||
| 0
|
-
|
0.5
|
Control Valve DP
|
1.4
|
| 0.5
|
-
|
0.67
|
Control Valve DP
|
1.8
|
This calculation will be checked for maximum flow with an oversizing factor of 1.1.
Control valve lift at minimum flow condition shall not be below 20% for equal percentage trims and not below 10% for linear trims.
Control valve calculations shall be executed on a computer programme, which is based to latest ISA standards (ISA-S75-1).
9.3 Piping Requirements for Control Valve Manifolds
Control valve will only be fitted with block and by-pass valves for the following application:
- When control valve size is 2 inch or smaller
- For critical services.
In all other cases the valve shall be fitted with a side-mounted handwheel only, except valves in a safety shutdown service, unless specifically noted.
The control valve manifold shall be shown on the engineering flow diagram.
Control valve shall be installed in horizontal lines with diaphragm operators above the valves. Butterfly valves shall be installed with the vane-shaft in horizontal position. For control valve manifold design see paragraph 12.7.
9.4 Self Acting Regulators
Regulators for flow, pressure and temperature with integarl actuator shall be used for control where loads are reasonably constant and requirements for precision and accuracy are less demanding.
Regulators shall be installed without by-pass manifolds except where they are necessary for emergency operation. Handwheels are not required.
A local indicator shall be provided at each regulator facilitate control point adjustment.
9.5 Control Valve Noise
The maximum allowable sound pressure level of 1 meter down stream of the valve and 1 meter away from piping sur face shall not exceed 85 dBa.
The estimated noise level of a control valve and the measurements to reduce the noise level when required will be determined in the engineering phase as per specification BN-SP-K3.
9.6 Safety Shut Off Valves
Valves shall have a fire safe design.
Actuator torque shall lie between 1.8 and 2.5 times the maximum break out torque at minimum specified air pressure.
Valves shall be “Tight Shut Off” (TSC). Valve seat leakage shall be equal or better than ANSI B16.104 (latest edition) class IV unless specified otherwise.
9.7 Valve Travel Time
The maximum allowable valve travel time (in both directions) shall be as follows:
Body Size Maximum Travel Time (sec)
1/2-3 inch 3
above 4” Equal to the nominal body size in inches
Valve travel time for burner shut-off valves be as per authority requirements.
9.8 Air Supply Buffer Vessels
Buffer vessels may be required to achieve the specified valve stroking or where an “air fail static” design is prescribed.
The design of the vessel shall be in accordance with the applicable codes.
10. Safety and Relief Valves
10.1 General
Safety and relief valves shall meet requirements of the ASME Unfired Pressure Vessel Code, API RP 520, and API RP 521, and API RP 526.
In addition, local codes will also apply. The highest requirements shall goven.
Safety valves for general process servoce have high lift characteristics. Thermal relief valves will be manufacturer’s standard.
For proper operation safety valves are generally at least set at 1.7 bar g or 10% above operating pressure whichever is greater above normal operating pressure.
10.2 Rupture Disks
Rupture disks will be narrow face capsule type, to fit inside the ID of the bolt circle of standard flanges.
Where a rupture disks is installed upstream of aafety valve, a device must be installed downstream of the disk to prevent any back pressure on the disk, and to detect leakage or rupture.
Inconnel disk shall be used for temperatures above 100°C where possible.
10.3 Piping Requirements
10.3.1 Inlet Piping
Maximum pressure drop between pressure source and safety valve inlet shall not exceed 3% of safety valve set pressure or 0.2 bar whichever is greater.
10.3.2 Disposal of relieved vapors or liquids
.1 Discharge to closed system
Any safety or relief valve discharging to a closed system shall be installed so that the discharge piping slopes into the header
If this is not possible, a 3/4 inch drain line shall be installed from the lowest point in the discharge piping to a safe area.
The drain line shall have 3/4 inch valve, normally closed, to permit periodic draining of the discharge piping.
In all cases, the discharge piping enter the header in the top or side.
.2 Discharge to atmosphere
All safety valves or vents discharging to atmosphere shall discharge at least 3 m higher than the top of the highest equipment within a radius of 15 m.
A 3/4 inch drain hole shall be provided at the lowest point in the safety valve riser. Care shall be taken that a flame can not impinge on equipment or piping.
10.3.3 Location of Safety and Relief Valves
A safety valve or relief valve shall be located with reset to platforms such that it can be serviced without ladders or scaffolding.
11. Reference Specifications and Standards
11.1 Company Specifications
| BN-SP-C2
|
:
|
Piping Specification.
|
| BN-SP-K2
|
:
|
Engineering and Design Specification for the Accesibility of Instruments.
|
| BN-SP-K3
|
:
|
Engineering and Design Specification for the Limitation of Control Valve Noise.
|
| BN-SP-K4
|
:
|
General Specification for Instrument Panels, Cabinets and Wiring.
|
| BN-SP-K5
|
:
|
General Specification for Signal Processing Systems.
|
| BN-SP-K6
|
:
|
General Specification for Control Valves.
|
| BN-SP-K7
|
:
|
General Specification for Instrumentation on Package Units.
|
| BN-SP-K8
|
:
|
General Specification for Installation of Instrumentation.
|
| BN-SP-K9
|
:
|
General Specification for the Fabrication of Orifice meter runs.
|
| BN-SP-K10
|
:
|
General Specification for Instrument Testing, Calibration and Acceptance.
|
11.2 Other Specifications
| ANSI B 40.1
|
:
|
Gauges - Pressure (and Vacuum). Indicating Dial Type.
|
| API RP 550
|
:
|
Part I - Process Instrumentation and Control Part II - Process Stream Analyzers.
|
| API RP 520
|
:
|
Recommended Practice for the Design and Installation of Pressure Relieving System in Refineries.
|
| API RP 521
|
:
|
Guide for Pressure Relieving and Depressurizing System.
|
| API RP 526
|
:
|
Flanged Steel Safety Valves
|
| ISA RP 3.2
|
:
|
Flange Mounted Sharp Edge Orifice Plates for Flow Measurement.
|
| ISA S 75.03
|
:
|
Uniform Face to Face Dimensions for Flanged Globe Style Control Valve Bodies.
|
| ISA S 75.04
|
:
|
Enviromental Conditions for Centralized Control Systems.
|
| ISA RP 75.06
|
:
|
Standard Control Valve Manifold Designs (Carbon Steel Valves only).
|
| ISA S 5.1
|
:
|
Instrumentation Symbols and Identification.
|
| ISA S 5.3
|
:
|
Graphic Symbols for Distributed Control/Shared Display Instrumentation, Logic and Computer Systems
|
| ISA S 75.01
|
:
|
Control Valve Sizing Equations.
|
| ISA MC 96.1
|
:
|
Temperature Measurement Thermocouples (ANSI Standard).
|
| ISO 5167
|
:
|
Oriffice Metering of Natural Gas, Gas Measurement
|
| SAMA STD PMC 33.1
USAS B 16.5
|
Radio frequency interference.
Steel Pipe Flanges and Flanged Fittings.
|
|
| ASME
|
Unifired Pressure Vessel Code.
|
12. Typical Drawings
12.1 Straight Length Requirements for Oriffice Flow Instruments
Minimum meter run for oriffice flow meters as per ISA 5167 figures are based on b = 0.75.
|
Downstream run
Orifice Small disturbances 90° fittings in same plane, vessel outlets Reducers, increasers eccentric swages, etc. Multiple fittings in same plane, tees, crosses with multiple outlets Multiple fittings in different planes Multiple fittings in different planes, tees, crosses with multiple inlets Control valves, globe valves and other valves which are used for throttling
|
Notes:
1. Minimum length of meter runs is based on ISO 5167 practices, for a maximum b ratio of 0.75. Where long meter runs interfere with practical piping layout and correct process design the upstream run might be determined using actual b ratio. Piping designer to consult the instrument engineer.
2. Take upstream and downstream meter run from the orifice.
When pipe taps are used, increase upstream straight run with 2 diameters and downstream with 8 diameters.
3. Where two or more disturbances exist, the distance between any disturbance and primary element shall not be less than defined in paragraph 12.1.
Therefore, it is required to consider also those disturbances more upstream, and not only the one close to the orifice. Refer to examples A and B below.
4. Install thermowells, instrument connections, etc., preferably downstream of the orifice.
Example A
Refer to paragraph 12.1.
Note 3
|
TWO BENDS IN SAME PLANE
When X 12(6)D, Y must 34(17)D When X 12(6)D, Y must 44(22)D However, the control valve must always be 88(44)D from the orifice plate. This is to be accomplished by increasing X, Y or Z or any combination of those.
|
Example B
Refer to paragraph 11.1.
Note 3
|
TWO BENDS IN DIFFERENT PLANES
When X 20(10)D, Y must 56(28)D When X 20(10D, Y must 70(35)D The reducer can be installed 38(19)D from orifice.
|
12.2 Instrument Connections on Piping and Vessels
12.2.1 Instrument Connections on Piping
12.2.2 Instrument Connections on Vessels
12.3 Installation of Instruments
12.3.1 Flow Instruments
.1 Close coupled flow transmitter, liquid service, meter below taps.
.2 Close coupled flow transmitter for steam or condensable vapour service, meter below taps.
.3 Close coupled flow transmitter for gas service, meter above taps.
NOTES
1. Restrict impulse leads to minimum length.
2. Provide positive slope, at least 1 inch per foot for all leads to avoid possible pocketing and provide positive venting or draining.
3. Connect high pressure side of instrument to upstream tap.
4. For liquid service in vertical lines, up-flow is preferred to avoid vapor or trash build-up above the plate.
5. Install meters above taps for liquid, steam or condensable vapor service.
6. Install meters above taps for gas service.
7. For steam service both fill tees must be installed at same centre line elevation as upper tap.
.4 Rotameter
When rotameter has top outlet and/or bottom inlet use similar arrangement.
|
Piping arrangment for metal tube rotameters. |
Piping arrangment for glass tube rotameters. |
12.3.2 Level Instruments
.1 External displacer and ball float switches.
Installation by piping.
Flanges and valves to be in accordance with piping spec.
.2 Gauge Glasses
Installation by piping.
Flanges and valves to be in accordance with piping spec.
 |
|
|||||||||||||||||||||||||||||||||||
.3 Differential pressure transmitter for level.
NOTES
1. Install seal pots for high displacement type instruments only.
2. Install additional block valve when required.
12.3.3 Pressure Instruments.
.1 Pressure gauge for gas liquid service.
.2 Pressure gauge with chemical seal.
.3 Pressure transmitter
12.3.4 Thermowells
.1 Typical screwed thermowell installation
|
|
|
|
90° installation, use for lines 6 inch and larger |
Elbow installation, use for 4 inch and smaller. 2 inch and smaller swage-up to 3 inch, as shown dotted. |
|
|
|
|
45° installation, use for 4 inch and smaller lines 3 inch and smaller swage-up as shown dotted |
.2 Typical flanged thermowell installation.
|
|
|
|
90° installation, use for all line sizes 3 inch and smaller swage-up to 4 inch. |
Elbow installation, use for 4 inch and smaller. 2 inch and smaller swage-up to 3 inch as shown dotted. |
|
Line size |
3” |
3” |
4” |
6” |
8” |
10” |
12” and larger |
Vessel |
|
Length “L” for screwed Thermowell |
NOTE 1 |
NOTE 2 |
5” |
5” |
5” |
5” |
9” |
9” |
|
Length “L” for flanged Thermowell |
NOTE 3 |
NOTE 3 |
9” |
9” |
12” |
12" |
12” |
12” |
| NOTE
|
1.
|
:
|
For 45° installation swage-up to 4 inch.
For elbow installation swage-up to 3 inch.
|
| 2.
|
:
|
For 45° installation swage-up to 4 inch.
|
|
| 3.
|
:
|
For 90° installation swage-up to 4 inch.
|
|
| 4.
|
:
|
Threadolet/elbolet/flange etc. in accordance with pipe specification.
|
|
| 5.
|
:
|
Wells for dial thermometers shall be installed to insure good readability of thermometer from grade or platform.
For type of dial thermometer check with instrument department.
|
12.4 Segregation of Cables in Trenches
On/off signals exceeding 40 watt rating be routed in the electrical trench.
12.5 Control System Philosophy
12.6 Power Supply and Distribution System (Typical)
|
Non vital Annunciators Analyzer Others |
Vital Relay boxes Solenoid valves Signal lights |
Vital Electronic signal Processing systems, loops Central receivers, Annunciators, Electronic logic etc. |
12.7 Control Valves
 |
|
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|
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GENERAL DESIGN REQUIREMENTS
1. Reduction in line size shall take place as close to control valve as practical. Where lines sizes upstream and downstream are not the same, the upstream block valve is based on upstream size, and the by-pass and downstream block valves are based on downstream size.
NOTE: By-pass valve might be sized larger when high capacity flow is required for flexibility. When by-pass controlability is important the by-pass size may be selected for a capacity of twice the selected control valve.
2. Block valves shall be at right angles to each other.
3. A 3/4” drain is installed between the upstream block valve and the control valve, on the bottom pipe. (Only necessary when on flow sheet).
4. Block, and by-pass valves shall be easily operable from grade or platform.
|
CONTROL |
LINE SIZE IN INCHES |
|||||||||||
|
VALVE BODY SIZE |
3/4 |
1 |
1 1/2 |
2 |
3 |
4 |
6 |
8 |
10 |
12 |
14 |
16 |
|
3/4
|
3/4 |
1 |
1 1/2 |
2 |
Recommended minimum block and by-pass valve size
|
|||||||
|
1 |
1 |
1 1/2 |
2 |
2 |
||||||||
|
1 1/2 |
1 1/2 |
2 |
2 |
3 |
||||||||
|
2 |
2 |
3 / 2 |
3 |
4 |
||||||||
|
3 |
3 |
4 / 3 |
4 |
6 |
||||||||
|
4 |
4 |
6 / 4 |
6 |
8 |
||||||||
|
6 |
When two valves are shown: |
6 |
8 / 6 |
8 |
10 |
|||||||
|
8 |
8 |
10 / 8 |
10 |
12 |
||||||||
|
10 |
10 |
12 / 10 |
12 |
14 |
||||||||
|
12 |
12 |
14 / 12 |
14 |
|||||||||
|
14 |
14 |
16 / 14 |
||||||||||
|
16 |
16 |
|||||||||||
12.8 Grounding and Screening
