STANDARD SPECIFICATION FOR LEVEL INSTRUMENTS DOCUMENT NO : 44-LK /J.02/0007-A4

Transcription

1 Page 1 of 8 STANDARD SPECIFICATION FOR LEVEL INSTRUMENTS DOCUMENT NO : 44-LK /J.02/0007-A4 Rev No. Issue Date Pages Rev Description Prepared A Issued for Comments / Approval By Checked By Approved By NSA SPM BSP

2 JACOBS ENGINEERING INDIA PRIVATE LTD STANDARD SPECIFICATION FOR LEVEL INSTRUMENTS Page 2 of 8 TABLE OF CONTENTS 1.0 PURPOSE 2.0 SCOPE 3.0 TECHNICAL REQUIREMENTS 3.1 LEVEL GAUGES 3.2 LEVEL TRANSMITTER 3.3 LEVEL SWITCH 3.4 TANK LEVEL INSTRUMENTS 3.5 MISCELLANEOUS 3.6 FIELDBUS DEVICES GUIDLINE 4.0 RELATED DOCUMENTATION 5.0 ATTACHMENTS

3 JACOBS ENGINEERING INDIA PRIVATE LIMITED STANDARD SPECIFICATION FOR LEVEL INSTRUMENTS Page 3 of PURPOSE 2.0 SCOPE The purpose of this specification is to define the minimum requirements of design and manufacture of Level Instruments. The scope of work shall include design, manufacture, testing and supply of Level Instruments. The inspection requirements shall be as per the inspection and test plan. 3.0 TECHNICAL REQUIREMENTS 3.1 LEVEL GAUGE Float operated magnetically coupled gauges with 2" (50 mm) flanged end connections, shall be used, for level gauging in very viscous liquids, liquids with crystals, sour services, toxic services and shall be of Bi-Colour rolling Cylinders/Balls. In general magnetically coupled level gauges shall be preferred over gauge glasses Bi-colour type level gauges shall be used on steam drums. Large chamber gauge glasses and an expansion loop between the top of the gauge and the top gauge valve shall be used. Level gauges on steam / boiler drums shall be in accordance with the latest requirements of the IBR code The Level gauge shall provide visible coverage of complete level transmitter / controller range and the alarm / trip level switches. In the case of differential pressure level transmitters where large spans are involved, a gauge located at the top, centre, and bottom of the installation with overlap in visible area shall be acceptable Magnetic coupled level gauges shall be preferred over gauge glasses. Where magnetic level gauges are not suitable for services such as high temperature etc steel armoured reflex or transparent type shall be considered. Wherever gauge glasses are considered, they shall be with body & cover material of forged steel and shall have mechanical & thermal shock resistant type toughened borosilicate glass with suitable gasket. Bolting shall be of SAE 4140 steel. Transparent type of gauges shall be provided with integral illuminators operating at 240 V 50 Hz supply and suitable for electrical area classification specified. Illuminator shall be of the plastic solid wedge type designed to give an even diffusion of light over the entire length of the gauge glass. All gauge glasses must have a rating equal to or more than the vessel design pressure and temperature and shall be provided with suitable metal guard Reflex type shall be used for clean and colourless liquids like water and hydrocarbon service, except liquids interface level. For low temperature, low boiling point service, foaming liquids, large chamber type will be used. Transparent type will be used for light fluids, acids, caustic, dirty or viscous liquids, coloured liquids and liquids interface level. Transparent type with Mica or Kel-F shields shall be used for treated water, boiler and condensate services and for corrosive liquids which will attack glass. Tubular gauge glasses shall, in general, not be used. They may be used for non-hazardous services at ambient temperature and low pressures All gauges shall have top and bottom chamber connections, unless otherwise specified. Vent and Drain valves shall be fitted, as applicable. Vent and drain valve shall be provided with nipple and end caps. Drain and vent shall be of welded construction. Level

4 JACOBS ENGINEERING INDIA PRIVATE LTD STANDARD SPECIFICATION FOR LEVEL INSTRUMENTS Page 4 of 8 gauges with side-side connections shall be avoided. Each gauge shall be provided with ball check valves & pipe union Large chamber gauges with frost shields shall be provided for cold services below 0ºC. Frost shield shall be transparent plastic type covering full width of vision slot and suitably sealed to the glass. Depth of Block Design Temperature 38 mm above 19 C 75 mm -20 C to 49 C 150 mm -50 C to 99 C 200 mm below -100 C Heating jacket shall be provided for viscous liquids The minimum readable liquid level from bottom tangent line for level gauge with top & bottom connections and when both the nozzles are from the side shall be 300mm with / without standpipe In general, the visible length of the level gauges shall be selected from the following: Visible length (mm) Centre to Centre Length (mm) The maximum visibility length shall not exceed 1500 mm for a single gauge. Multiple gauges with overlapping range shall be used for such cases. For a given section, the visible length shall not be less than 90% of the total length of section Gauge glass cocks shall be forged offset type with integral ball check and back seating stem. Primary isolation valves are normally required in addition to the gauge glass cocks, except on vented tanks containing harmless liquids. Where the process fluid tends to foul the cocks internals and create plugging or where leakage is a problem, gauge valve may be eliminated. On low temperature service with liquids having very high vapour pressure at ambient temperature safety valve shall be provided at the vent connection of the gauge glass. Gauge cocks may be deleted or ball checks omitted when the fluid is not toxic / corrosive / inflammable / at high pressure and when there is a possibility of sluggish action. If ball checks are used, it shall be checked that the process pressure is high enough to drive the ball in case of breakage. 3.2 LEVEL TRANSMITTER External displacer type instruments with side-side connections and rotatable head shall normally be used for level measurement upto 1219 mm. Side-bottom connections are preferred where RTJ flanges are required. Internal displacer type of level transmitters shall be avoided unless application necessitates its use. Stilling well shall be provided for internal displacer Conventional Electronic transmitters shall be two wire, 24 VDC, 4-20 ma output with 'HART' Protocol. Specifications for DP type level transmitters shall be as elaborated in Standard Specification for Pressure/DP Instruments A separate Hand held communicator with necessary software for communication loaded shall be provided along with displacer level transmitters.

5 JACOBS ENGINEERING INDIA PRIVATE LIMITED STANDARD SPECIFICATION FOR LEVEL INSTRUMENTS Page 5 of All displacer type level transmitters shall be of torque tube type with torque tube material of inconel, as a minimum. Accuracy of displacer type level transmitters shall be +/- 0.5%. The standard materials shall be as a minimum: - Displacer : 316 SS Torque tube : Inconel Chamber : Carbon Steel Finned torque tube extensions shall be provided as necessary for high or low temperature service conditions In general, displacer type instruments shall be used with displacer lengths of 356 mm, 813 mm and 1219 mm. For interface level measurement, displacer type instruments shall only be used Differential pressure transmitter shall be used for level measurement above 1219 mm for services requiring purge or where liquid might boil in external portion Differential pressure transmitters for use on corrosive or fouling service shall generally be diaphragm wafer with filled capillary type. Flush or extended diaphragm type differential pressure transmitter shall be considered for special applications only. Diaphragm material shall normally be stainless steel or any other special alloy. Transmitters for closed vessels shall have correction for suppression or elevation Dip Tube type level transmitters may be used on corrosive, congealing, slurry services where suitable diaphragm seal type transmitter is difficult to obtain or where accuracy is not of prime importance For Hot service applications Radr type level transmitters shall be considered when suitable. 3.3 LEVEL SWITCH In general level switches shall be avoided. However, when specified, level switches shall generally be external ball float type with flanged head. External displacer type level switches can be considered for lighter fluids where specific gravity is less than 0.5. Internal float / displacer type level switches shall only be used if external ball float / displacer type is not possible, like in viscous services and in underground tanks / vessels The low-level switch shall be mounted directly on the column when the set point is not less than 630mm. When level gauge and level switch are on the same standpipe, the minimum allowable low level set point shall be 480mm on the column Switch shall be sealed micro type with contact rating suitable for the specific application. Level switches with reed switch shall not be used Level switch shall be furnished with SPDT contacts with adjustable differential, unless otherwise specified.

6 JACOBS ENGINEERING INDIA PRIVATE LTD STANDARD SPECIFICATION FOR LEVEL INSTRUMENTS Page 6 of Tuning fork, capacitance, displacer or paddle type level switch may be used wherever application calls for such device. 3.4 TANK LEVEL INSTRUMENTS Mechanical float type gauge shall be used for atmosphere tanks and vessels where level measurement accuracy requirement is of the order of ± 2 mm. Liquid seal chamber shall be used where tank contents are toxic or tank is blanketed. The float shall be of 316 stainless steel as a minimum. Cages shall be carbon steel as standard unless service conditions demand a higher specification Servo controlled gauges shall be used for level measurement of pressurised tanks / vessels / spheres requiring remote signal transmission and better level measurement accuracies. Level / data transmission signal shall be digital only. Servo type instruments shall have 6" process connection with 12" dia still well. The accessories for servocontrolled level gauge shall include calibration chamber, operator keys for moving the displacer and isolation ball valves for pressurised tanks The tank side indicator for both types of gauges shall have hoisting facility. All tank level gauges shall have side mounted indicator - counter type for mechanical float type and solid state digital for servo controlled level gauge RADAR type tank gauges shall be used for storage tanks handling viscous fluids, pressurised tanks or as specified in job specification Hydrostatic tank gauging system can be used for high accuracy measurement if the application calls for same The wetted material like float, displacer, tape, wire etc. shall be minimum 316 SS. 3.5 MISCELLANEOUS Other special type of level instruments like RADAR, ultrasonic, hydrostatic, nucleonic, capacitance, conductivity and magnetostrictive type shall be used as necessitated by application requirements For high-pressure steam drum application, conductivity type (Hydrostatic or equivalent) level instrument shall be preferred For solid level measurement, type of instrument shall be ultrasonic / RADAR / paddle / electromechanical / capacitance / nucleonic. The actual type selection shall be carried out based on the provenness of the selected type for the similar type of application Standpipe shall be used for clean, non-viscous and non-crystallising services if more than 4 nozzles are required for level instruments, e.g. one displacer instrument and one level gauge can be mounted directly on the equipment. The maximum number of nozzles on the standpipe shall be limited to: - 8 nos. with no displacer type level instrument on it 6 nos. with displacer type level instrument on it. The size of standpipe shall be 2 NB minimum and valved at the instrument connections.

7 JACOBS ENGINEERING INDIA PRIVATE LIMITED STANDARD SPECIFICATION FOR LEVEL INSTRUMENTS Page 7 of 8 Trip level switches should be directly mounted on vessel / column and not on standpipe. Connection of standpipe from the bottom of vessel should be avoided. On horizontal vessels with boot, separate standpipe shall be used for boot interface level measurement in addition to standpipe used for horizontal vessel Level co-ordination sketches shall be produced showing all pertinent details including nozzle locations, alarm levels, shutdown levels, normal liquid levels and dimensional details All displacer and float type instruments shall have provisions for on-site calibration simulation check Differential pressure type transmitters used for level measurement shall be calibrated using wet leg. A provision shall be made for liquid filling during installation. 3.6 FIELD BUS DEVICES GUIDELINES The Field bus transmitter shall be 2 wire system and shall have minimum facility as - Foundation fieldbus output compliant to ITK 4.6 or above. - Shall employ device description to facilitate interoperability It shall not be sensitive to the polarity of the wiring connection It shall operate on 9 to 32 V dc, with current draw capacity of 17mA maximum. This low power consumption shall allow more devices to be connected to a segment The digital integral LCD display shall be capable of displaying any other variable from any device on same segment Vendor to specify Response time (including dead time, time constant and min damping) The foundation fieldbus transmitter must have the following essential facilities to facilitate complete FF functionality including control in the field as and when required. - Shall have multiple FF compliant analog input (AI) blocks (2 Nos with execution rate of 30 ms or below) and VCRs (at least 12 Nos or above) to allow control in the field Multiple AI blocks shall provide flexibility in using transmitter data for calculations and alarming, while VCR s used for communication between function block both within a device as well as amongst different devices shall be sufficient to execute all inter block data transfers. - Shall have a characterizer block for strapping tables. - Shall have a integrator block for totalisation. - Shall have a arithmetic block for functions such as level or density calculation. - Shall have a input selector block for voting or averaging applications. - Shall have a PID function block with PID. - Shall provide a back up link active scheduler ( LAS) so as to improve the reliability and security of the FF network. - Shall have software download capability for upgrades or product enhancement via fieldbus segment with the segment in operation. - Shall have guided routine (methods) for calibration and restoration of sensor defaults. - Shall have block execution times less than 45ms.

8 JACOBS ENGINEERING INDIA PRIVATE LTD STANDARD SPECIFICATION FOR LEVEL INSTRUMENTS Page 8 of Diagnostics The transmitter shall perform continuous self diagnostics, be capable of self test functions and be able to provide specific diagnostic information locally on the LCD meter and remotely via digital FF communications protocol. The diagnostic capabilities shall include the following features- - Shall detect and alert or alarm during process abnormal situations using statistical methods. - Shall provide a variety of standard statistical monitoring configuration defaults for detection such as plugged impulse line detection and flame instability. - Shall have an easy system for alerts and understanding of faults, failures and anomalies either in the sensor, electronic circuits or process. 4.0 RELATED DOCUMENTATION Nil 5.0 ATTACHMENTS Nil