Theory

Instrument Hook Up Diagram is also called Installation drawing, specifies the scope of work between Mechanical and Instrumentation departments. Hook up diagram is generally referred at the time of procurement of consumables required at the time of installation and while actually installation work on site is carried out. Instrument Hook Up Diagrams detail the accessory and tubing hookup for both process and field instruments based on the tag number. Generally included are:

• Tag number

• Numbers of the loop drawing

• Layout & routing drawing and isometric piping drawing containing the particular control loop component

• Elevations of both the primary control loop component and process connection

• Tagging of mechanical (piping or equipment) to instrumentation interface

• Tagging of all elements/fittings & valves with item numbers

• Direction of slopes in hook-up lines

• Elevation of Instrument

• Maximum allowable lengths of hook-up lines

• Accessories often detailed include Mono-flanges, Double Block and Bleed Valves and Fittings etc

• Material take off with part numbers, number of particular fittings, size, connection, material type, mounting type

• Weather shield and tubing specification

Before installing the field instrument the site engineer need to pay attention towards following points:

• Check Tag No of particular instrument or list of instruments

• Scope of work between mechanical and instrumentation

• Bill of material such as SS fittings, Tubing, Isolation valves, plugs, manifold block, Transmitter bracket mounting type (Vertical or Horizontal) mounting bracket type

• Check for bulk material for each installation

• Type of material to use to measure based on fluid and its parameters

• Position of instrument in reference to process tapping point

• The tubing slopes need to be paid attention