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Instrument Air Supply QAQC Questionnaires

Instrument Air Supply

4. Designs (J‐901)

4.1 General

4.1.1 Instrument air supply systems shall provide dry, oil‐free air to pneumatic

instrumentation, valve actuators, and other services requiring instrument‐quality

air.

4.8 Instrument Air Distribution System

4.8.1 General Requirements

4.8.1.1 Piping material shall be selected in accordance with SAES‐ L‐032. The

selection of alternative piping material requires the approval of the

Coordinator, Mechanical and Civil Engineering Division/CSD.

4.8.1.2 All main and branch headers shall be sloped {minimum 64 mm per 30 m

(2.5 inches per 100 feet)} and provided with low point drains.

4.8.1.3 All headers shall terminate with a line‐size valve, blind, or plug to

facilitate cleaning and plant expansions.

4.8.1.4 Each branch header shall connect to the top of the main header through

a branch‐line‐size, full‐bore isolation valve.

4.8.1.5 Where there is a general distribution system for more than one

plant, the piping shall be connected in a loop to provide two directions of

supply to each plant. Isolation valves shall be provided to enable

isolation of each plant.

4.8.1.6 Supply takeoffs to individual instruments (a line serving up to a maximum

of four devices) shall connect to the top of the branch header through a

takeoff‐line‐size, full‐bore isolation valve.

4.8.1.6.1 The minimum size of supply takeoffs is ½‐inch.

4.8.1.6.2 Twenty percent (20%) spare takeoff fittings and block

valves shall be installed on the branch header.

4.8.1.7 Instrument air piping shall not be pocketed (i.e., shall not contain, Usections).

Instrument air piping shall not be installed underground.

Exception:

Instrument air branch connections may be buried to cross beneath roadways or

fences where there is no existing overhead rack and where the aboveground

support would interfere with crane or emergency vehicle movement. Prior

approval from the General Supervisor, Process Instrumentation Division, P&CSD

is required. Buried branch lines shall have low point drains, stainless steel

construction and external coating per SAES‐H‐002.

4.8.2 Header and Takeoff Sizing

4.8.2.1 The pressure drop for piping between the dryer after filter outlet and the

most remotely located user shall not exceed 35 kPa (5 psi) under

maximum service flow rate.

4.8.2.2 For installations in which the instrument air consumers are located more

than 600 m (2000 ft) from the instrument air compressor; pipe sizes

should be calculated to keep pressure drops within the above limit.

Below 600 m (2000 ft) instrument air header pipe size should be

selected from Table 2. (J‐901) 

5 Testing (J-901)

Pressure testing of supply system and distribution system per SAES‐L‐056, using

dry instrument air or inert gas is required. Hydrostatic testing of instrument air

piping is not permitted.

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