Feb 21, 20213 min read

What Instrument Hook up Diagram is (Hook up Drawing)?

In the previous article, we all learn the Piping and Instrumentation Diagram(P&ID) which is the most used drawing in the process industries.

In this article, we will learn instrument hook up drawing with example. You can create hook up drawing using Autocad software.

Instrument Hook Up Diagram:

Instrument Hook Up Diagram is also called Installation drawing, specifies the scope of work between Mechanical and Instrumentation departments.

It is a detailed drawing showing typical installation of an instrument in a correct manner, from the tapping point in the process line up to the sensing instrument, so that the instrument operates properly and prevent issues that could potentially affect the measurement such as liquid trap in gas impulse.

The Hook-up drawing indicates the slopes of the tube, the position of the instrument in reference to the point of tapping of the process, the breakage of the reach between the instrument and the pipe.

It also provides information on the requirement of bulk material for each installation.

There are two types of hook-up drawing:

1) Process Hook-up:

which contains the installation of the instrument for process control.

2) Pneumatic Hook-up:

This hook-up drawing contains typical installations for instruments that require air for instruments, such as the control valve.

The instrumentation Construction Engineer has to review and verify certain important points before going for an Instrument erection. 

Check Tag No of a 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 the instrument in reference to process tapping point. The tubing slopes need to be paid attention.

Instrument Hook Up Diagrams detail the accessory and tubing hookup for both process and field instruments based on the tag number.

It should include standard specifications for the welding of hook-up piping, heat tracing & insulation and pressure testing & painting requirements.

Generally included are, 

1. Tag number 

2. Numbers of the loop drawing

3. Layout & routing drawing and isometric piping drawing containing the particular control loop component. 

4. Elevations of both the primary control loop component and process connection. 

5. Tagging of mechanical (piping or equipment) to instrumentation interface 

6. Tagging of all elements/fittings & valves with item numbers. 

7. The direction of slopes in hook-up lines. 

8. Elevation of Instrument. 

9. Maximum allowable lengths of hook-up lines. 

10. Accessories often detailed include Mono-flanges, Double Block and Bleed Valves and Fittings etc. 

11. Material take off with part numbers, a number of particular fittings, size, connection, material type, mounting type. 

12. Weather shield and tubing specification.

Difference between Hook-up and P&ID drawing:

- Piping and Instrumentation Diagram (P&ID) shows the instruments that are to be connected to a process line, the Instrument Hook-up gives detail information about how that is to be done during the actual installation.