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PRESENTATION

INSTRUMENT HOOK-UP

(PROCESS & ANALYZER)

Prepared By : M. Asim Ashraf

Date : 16-10-2000

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CONTENTS INTRODUCTION GENERAL CONSIDRATION CONSIDERATION REGARDING

ROUTING SYSTEMS OF PROCESS HOOK-UP SEALING PURGING HEATING ANALYZER HOOK-UP

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INTRODUCTION

PROCESS HOOK-UP (IMPULSE LINE)Process hook-up conveys the process fluid to the relevant instrumentation for measurement of the process variable.

TYPES OF PROCESS HOOK-UP

1. SHORT PROCESS HOOK-UP

2. LONG PROCESS HOOK-UP

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SHORT PROCESS HOOK-UP When the instrument is mounted close to the process

connection (such as a transmitter, or a local pressure gauge) the impulse line is short and is usually made from tubing with compression fittings.

LONG PROCESS HOOK-UP when the instrument is mounted in a panel, the impulse

line is much longer.Steel piping may then be required because it has better mechanical strength and allows greater distance between supports.NOTE :Except for very light instruments, example locally mounted pressure gauges, the instrument should not be supported from the impulse line, unless direct mounting requested using short nipple pipes.

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THE ACCESSORIES REQUIRED IN PROCESS HOOK-UP:

Vent plugs or valves on high points in liquid-filled lines.

Drain plugs or valves on low point in gas or vapour filled lines.

Filling plugs or valves where the line needs sealing liquid.

Purging and neutralizing connection for lines and instruments in toxic and/or noxious applications and for low pour point fluid.

ACCESSORIES

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GENERAL CONSIDRATION

Line length shall be short as possible ;

For fast response and less inaccuracy. To avoid possible blockage. To avoid mechanical damage (rupture proceed potential

danger situation). To save material cost. To save required installation space. For all impulse lines the pressure rating under operating

temperature should be verified.

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CONSIDRATIONS REGARDING ROUTING

Impulse line should not obstruct passage the process plant.

Not interfere with accessibility to removal of process

equipment (pumps, motors & heat exchanger).

They should be routed away from hot / freezing

environment

Should be routed away from potential fire risk

Should be routed away from mechanical abuse

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The lines and their supports should be kept free from

vibrating structures or equipment.

Impulse line should be laid in the open on angle iron

brackets connected to the plant structure, or on existing

supporting beams, etc., where possible. Where necessary

impulse lines should slope continuously upwards or

downwards, with drain or vent facilities at the lowest or

highest points, respectively, depending on service.

Consider thermal expansion loop/bend for high

temperature and cryogenic services as the process tapping

points move lot.

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SYSTEMS OF PROCESS HOOK-UP

TUBING AND COMPRESSION FITTINGS

PIPING

CAPILLARY TUBINGS

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TUBING & COMPRESSION FITTINGS

The maximum allowable working pressure and

temperature for tubing (and fittings) should be verified.

Tubing can not be used to carry the weight of pressure

gauges, seal pots, etc. These items should be supported

by steel piping, nipples, fittings, or dedicated support.

The tubing should be carbon steel or stainless steel, cold

drawn, annealed. For non-flammable fluids other

materials such as copper tubing may be considered, with

approval of the client.

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Tubing with 12 mm overall diameter is suitable for most

application (10 mm may be selected for clean service or

client request). Wall thickness should be selected for

working pressure. The body material for the compression fittings should be

compatible with process conditions, the compression

ring should be compatible with the tubing material. For applications subject to serious vibration,

compression fittings having an additional O-ring of

resilient material should be considered.

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Flow transmitter with compression fitting and tubing

(Line Mount Case)

Flow transmitter with compression fittings and tubing

(stainless steel)

Equalizingvalve assembly

steel tube10mm stainless

Screwed valve

(Compression type)Stud coupling

clamped to pipe

line pipe50 mm

Welded or

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PIPING Line-pipe, (1/2” nominal size) and screwed or socket-

weld fittings should be used for long process hook-up, or where operating conditions are above the maximum values, for tubing and compression fittings.

For dirty gases and /or low pressure measurements for example furnace pressures, 3/4” to 2” diameter pipe may be necessary.

Material for piping and fittings should be carbon steel except where corrosive conditions require other materials such as stainless steel, monel etc.

Piping with PTFE or other lining may be required for applications for which no suitable metallic material can be found.

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Flow transmitter with socket weld fitting and line pipe(Line Mount Case)

Flow transmitter with socket weld fitting and line pipe

Flange

clamped to pipe

line pipe50 mm

Welded or

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CAPILLARY TUBING Instrument having long lengths of capillary tubing

between the detector head and the measuring instrument are not recommended as a general practice, but where they are used, the following precautions should be observed:-

(i) The capillary tubing should not pierced, stretched or twisted, otherwise permanent damage to the instrument is caused.

(ii) Bends should be to a minimum radius of 0.1 m. Any excess length of capillary should be neatly coiled at the measuring instrument and clipped in coil not less than 0.2 m diameter.

(iii) Capillary runs should be protected e.g., clipped to a cable tray or suitable light gauge angle.

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SEALING Process fluids which solidify or are highly viscous at the

lowest ambient temperature, should be prevented from entering impulse lines and instruments.

For high elevation nozzle side tubing of differential pressure type level instrument may be filled by seal liquid (wet leg) to prevent ready error during start-up.

In the situation, impulse lines and instruments should be filled with a suitable seal-liquid, which

(i) Will not solidify.

(ii) Will not mix or react with the process fluid.

(iii) Will not evaporate under process conditions.

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PURGING Purging by means of a suitable gas or liquid is

sometimes required to prevent corrosive process fluids from entering process hook-up and instruments, or to prevent blockage of process connections and process hook-up arising from solid particles, choking or polymerization of the process fluid. Care should be taken to ensure that the purge lines are connected to a maintained supply which is always at a pressure above that of the process fluid keep by constant flow, and that the purging medium does not react with the process fluid or affect its specification.

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Each purge line should be provided with a check valve and a constant flow regulator,(preferably with a small variable area meter). These are necessary to keep the purge flow constant under the following conditions:

(i) Variations in purge supply pressure,

(ii) variations in process pressure,

(iii) Increase in resistance to purge flow, due to partial plugging of lines or connection.

Where constant flow regulators are not possible, fixed restrictions (e.g. Restriction orifice plates) should be applied

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Stainer

Orifice

SupplyPurge Liquid

Restriction

Check Valve

Union

Flow transmitter with liquid purge

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HEATING The heating of impulse lines and instruments should only

be considered when other possibilities such as seal liquids cannot be applied. In any case, overheating of the instruments should be avoided.

Where heating is necessary, full use should be made of process-heat, e.g. by including the first part of the process hook-up (up to seal) inside the lagging, or by installing protective covers over the process-pipe, the process hook-up and measurement chamber of the instruments.

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Where the above is not possible, external heat sources should be considered. Stream is most commonly used, but hot water or hot oil heating systems should be considered when present for other purposes, e.g., for tank heating or tracing of process piping. Electric heating should only be used where compatible with the safety requirements for the specific application or precised temperature control is required.

Under very adverse climatic conditions it may be necessary to install the entire instrument in a heated housing. This would consideration increase the installation cost, and should only be considered when absolutely necessary. If fitted the housing should not interfere with free access to instruments and impulse lines. Thermostatically controlled electric heating should be preferred to prevent overheating of the instrument.

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ANALYZER HOOK-UP Almost all requirements considerations for process hook-

up are applicable, however following point shall be taken into account for the design.

1. Follow vendors requirements for piping/tubing of process fluid (sample line) and utilities:

2. Sample line size shall be selected considering sample transportation time delay and required measuring cycle.(sometime 1/8” tubing may be required)

3. Sample is flowing in sample line where as no flow in process hook-up tubing. Material selection shall be made based on the process temperature & pressure.

Heat tracing may be required to keep sample temperature.