Hook up drawings for pressure transmitter
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For high pressure applications, gauges shall have a solid front design, blow-out rear and seals where application requires them. Also Hookups are required for Operation and Maintation. Con Hookup drawing is use to specify the Scope of Piping Department and Instrumentation Department. Diaphragm seals shall be ordered as an integral part of the instrument. As a good engineering practice, it is advisable to obtain confirmation on material of construction selection from metallurgy expert. Gauges shall be sincere IP 65 or IP 54 as a minimum Ingress Protection rating may change project to project. Unless specified otherwise pressure gauges shall have ½ inch NPT M bottom-connection and shall be direct mount type.
Introduction Fluid pressure is defined as the measure of force per-unit-area exerted by a fluid, acting perpendicularly to any surface it contacts. Pressures and pressure measurements can be extremely complex and complicated. However, if the proper techniques are used, it is possible to obtain accurate pressure measurements. Selection of pressure instrument for a particular application must be done carefully, taking into consideration various aspects such as process conditions including the metallurgy requirements, turndown requirements, accuracy, installation requirements etc. While selecting a pressure instrument for a particular application, the process data such as fluid phase, pressure, temperature, density and viscosity must be correctly defined for all operating conditions including start-up, emergency operations and design conditions. One typical case is that of a Compressor which has tripped without de-pressurization. Under such condition the Compressor suction pressure will be higher than the normal operating suction pressure and the transmitter should be calibrated to suit this pressure value. Another important parameter for selection is the turndown requirements, based on which we can select the pressure instrument to suit the maximum and minimum conditions within its specified accuracy limits. In addition to the above, the installation requirements of the selected pressure instrument shall be carefully addressed taking in to account visibility, accessibility, because these requirements may affect the piping layouts. Categorization of Pressure Instruments The most commonly used pressure measuring devices in industry are pressure gauges and pressure transmitters. Local Instrument Gauges can be further classified in two categories a Pressure Gauge b Differential Pressure Gauge Transmitters Transmitters can be further classified in two categories a Pressure Transmitter b Differential Pressure Transmitter DPT. DPTs are used for Differential Pressure measurement, Level measurement, Flow measurement. With rule of thumb, the selection of wetted parts to be identical to that of Valve trim mentioned in respective Piping material specification as a minimum. Special attention shall be paid to corrosion from the surrounding atmosphere for instruments and ancillary equipment. The numerous environments in which the meter can be used make it difficult to define process fluid compatibility for every possible material combination. The difference in chemical composition of most environments can be characterized by four variables. These are halogen E. The sensor diaphragm material or the diaphragm seal material shall be with Gold plating. When flanged diaphragm seal pressure instruments are used, it is important to verify the P-T rating Pressure — Temperature where diaphragm flange material is AISI 316 SS and the process connecting flange is of carbon steel. Smaller sizes may be accepted on instruments to be used for pneumatic supply. In some cases dial size may be 150 mm based on project specifications. For high pressure applications, gauges shall have a solid front design, blow-out rear and seals where application requires them. Definition of High pressure may vary project to project and this needs to verify prior to specifying this particular requirement. Unless specified otherwise pressure gauges shall have ½ inch NPT M bottom-connection and shall be direct mount type. Type of thread shall be stamped on shank. They shall be isolated from process using Double Block and Bleed valve DBB or Single Block and bleed valve SBB. Process isolation is dependent on Project Isolation philosophy. Further at pressure gauge end, mono-block assembly may be used if called upon in project instrumentation philosophy. Gauges shall be provided with an external zero adjustment mechanism. Casing material shall be either phenolic or AISI 316 stainless steel minimum, glass shall be shatterproof safety glass, retained by screwed or bayonet type bezel ring complete with a suitable gasket. Gauges shall be rated IP 65 or IP 54 as a minimum Ingress Protection rating may change project to project. Where excessive vibration is probable, liquid filled dampening devices shall be used. Typical example of excessive vibration is pressure gauge installed at pump discharge. Based on standard ranges available with reputed suppliers, following ranges are generally specified. However this is not the limitation. If pulsation is present in the process, maximum operating gauge pressure should not exceed 50% of the full-scale range. Gauges shall have accuracy equal to 1% of span, including hysteresis, linearity and repeatability. This accuracy is to be maintained after momentary overpressure and cycling up to 1. Where bourdon tube type gauges are not suitable due to corrosion, plugging, etc then pressure gauges with diaphragm seals are used. Typical Pressure Gauge 2. Also in case if the fluid temperature under any normal or abnormal operating condition exceeds the maximum allowable temperature of the sensing element Diaphragm Seal shall normally be integral with the instrument. The application of diaphragm seals with capillary extensions shall be kept to an absolute minimum. The complete diaphragm seal assembly shall be of welded construction. Screwed connections shall not be used. For transmitters, the capillary tubing shall be welded directly onto both ends of the sensor. Diaphragm seals shall be ordered as an integral part of the instrument. Wafer type Diaphragm Seal Special attention shall be paid to diaphragm seals on low differential pressure and pressure applications. For low pressure measurement good practice is to increase the size of sensing element so that minor changes are captured. When a diaphragm seal is required, the largest practical diaphragm size and minimum capillary size should be applied. Diaphragm seals shall be ordered as an integral part of the instrument. The length of the capillary tubing shall suit the application but shall be at least 1 meter. For differential pressure applications with two remote seals, the two parts of the capillary tubing shall be of the same length to nullify the inaccuracy caused by varying ambient conditions. If capillary tubing is exposed to direct sun radiation or to extreme temperature fluctuations e. Filling liquids shall be selected in consultation with the party responsible for the process design and with the Manufacturer. Filling fluids for capsules and diaphragm seals shall not present a hazard to the environment in the event of a diaphragm failure. Special attention shall be paid to diaphragm seals used in vacuum service, i. Filling liquids and connections shall be suitable for vacuum service as well special attention shall be paid to the use of diaphragm seals handling small ranges typically 50 mbar or smaller and interface level measurement. Facilities shall be provided to test and calibrate the diaphragm seal type transmitters under operating conditions. In case of wafer type or diaphragm seal with back-up flange, back-up flange is a non wetted part, possibility must be checked to use back-up flange with material of construction of Carbon steel. This arrangement is a cost effective solution and acceptable in industry. However Pressure — Temperature rating check shall be done thoroughly prior to completion of Technical evaluation ii Gauge Saver Gauge saver also known as over pressure protector and use to protect the pressure gauge from over pressure. The gauge saver has a predefined set-point at which it will not allow any media to flow. The set-point typically can be varied for a max span of 10% of set pressure. However based on application, additional features are as described. Differential pressure gauges shall be equipped with diaphragm or bellows elements, unless otherwise specified on the project data sheet. Gauges shall be capable of withstanding over-range pressure on either side of the diaphragm, without damage or calibration shift. Similar to pressure gauges the Differential Pressure gauges shall also be specified with solid front design if the line pressure is high even though the differential range may be small. Manifold is required for Differential Pressure gauge. However based on its design, the manifold may be required of external mounting type. The use of pneumatic transmitters for local loops shall be minimized. The normal pressure shall be read at no greater than 75% of the calibrated span for transmitters reading steady pressure. For fluctuating services the normal pressure shall be read at 60% of the calibrated span. Differential pressure transmitters, to be used on flow measurement, shall be configurable for square root or linear output. For low-pressure ranges between -1 barg, and +2 barg, differential pressure instruments shall be used for pressure measurement applications. The electrical signal transmission shall normally be 2-wire system, 4 to 20 mA, 24 V DC. When FF transmitters are selected, following capabilities should be addressed suitably: i Function Blocks ii Link Active Scheduler LAS iii Advance Control function Block iv Compensated mass flow block v Advance diagnostics Highway Addressable Remote Transducer HART protocol should be used for ESD system. Transmitters connected to ESD system shall be selected with minimum SIL2 certification. The pneumatic signal transmission range shall be 0. Where process pulsation exist a transmitter with inherent damping and adjustable damper shall be used. Transmitters shall have an overall accuracy, including repeatability, equal of 0. Transmitter body rating shall be 100 barg as minimum. Differential pressure transmitters shall be capable of withstanding over-range pressure on either side of the sensor element at least equal to the body rating without damage or calibration shift. For example: calibrated range 0 to 10,000 mbar, Body rating 100 barg, Line pressure max 60 barg. Enclosure shall be rated IP 66 as minimum with M20 x 1. Enclosure material shall be stainless steel for harsh environments. As an alternative, aluminum with epoxy painting, suitable for offshore marine environment, may be considered after obtaining formal approval from Client for the same. In general, All electronic transmitters shall have an integral indicator unless otherwise specified. These shall be of the Liquid Crystal Display LCD type and shall be configurable to read in percentage or engineering units. The integral indicators shall be suitable for the location and hazardous area classification. The construction of the indicator shall ensure instrument continuity in the event of indicator failure. Special attention shall be given to transmitters installed in ambient conditions where temperature is less than -20 deg. Heated enclosures or heated insulating jackets need to be provided to prevent the freezing of local LCD indicator below -20 deg. Usually, these manifolds are mounted directly on Pressure transmitter Integral mounting. Material of construction of manifolds shall be AISI 316SS as a minimum or superior based on application. Packing Material to be selected based on process temperature limits. Two Valve Manifold vii Three Valve Manifold For Differential Pressure transmitters, three valve manifolds are used. Usually, these manifolds are mounted directly on D. For Differential Pressure Gauge, integral type of manifold should not be considered. Externally mounted manifold should be used. Packing Material to be selected based on process temperature limits. Usually, these manifolds are mounted directly on D. These rings are required only when Diaphragm seals are used. In-Situ calibration is also possible if drip rings are used. Drip ring size and rating shall be suitable for selected diaphragm seal. Material of construction of drip rings shall be identical to that of vessel trim or as indicated in Piping Material Specification. As a good engineering practice, it is advisable to obtain confirmation on material of construction selection from metallurgy expert. Illustrations are typical and requirements may vary project to project.
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