A hook-up drawing is a detailed drawing showing typical installation of instruments in the correct manner so that the instrument operates properly (gives accurate indication and prevents any issues which could potentially affect the measurement such as liquid trap in a gas impulse line).
Hook-up drawings indicate tubing slopes, position of instrument in reference to process tapping point, and scope break between instrument vs piping.
Hook-up drawings also provide information of bulk material required for each installation. It also details its specification (size, type and material) and quantity.
There are two types of hook-up drawing:
- Process Hook-Up: drawing contains typical installations for instruments which connect to the process
- Pneumatic Hook-Up: drawing contains typical installations for instruments which require instrument air such as a control valve or an actuated valve
P&IDs tell the designer which instruments require a hook-up drawing. A good designer can also read whether the instrument is tapped in a gas service or liquid service. Battery limit between instrument and piping shall be made clear. This is stated in P&ID symbols and typical sheet or piping documents. Installation detail specification will also specify items that should be utilized and factors that should be considered during installation.
The Purpose of an Instrument Hook-Up Drawing
Information on the bulk material required for a project is stated on each sheet hence providing the bulk material required for the entire project can be summarized and tabulated in a document called Material Take Off.
During the project construction phase, hook-up drawings are used as a guide to demonstrate proper installation procedures.