COMPRESSOR PIPING

TYPES OF COMPRESSOR

Specific Guidelines on Piping

These tips are general in nature. For a specific unit consult the manual and/or manufacturer.

Inlet Air Piping

Rotary compressors:

Use dry filters or pressure aspirated oil wetted if unit has modulation control
For remote filter installation, remove filter from package to be installed:

No valves or obstructions in the inlet interconnecting pipe
Can use supported flex/rubber hose to pipe outside enclosure to connect to inlet pipe
If inlet is outside, be sure to install a bird deflector
Support inlet piping, do not hang on the unit
Be sure pipe is free of dust, rust, weld beads, scale, chips, etc. before starting the compressor
If running over 50 feet (confirm with manufacturer), increase pipe size at least one size or greater over the filter housing connection size

Reciprocating compressors:

Always try to increase inlet air piping one or two sizes above compressor connection size. Never reduce inlet pipe size from connection size on the unit
Brace/clamp pipe at regular intervals — DO NOT have pipe weight on compressor connection
Be sure pipe is clean and free from rust, scale, etc., before starting the compressor
Be sure you are not in “critical length” and if you are, consult manufacturers data for proper corrective action
Use inlet pulsation bottles when possible on larger units. Be sure bottle is clean before starting the unit
Can use dry or oil bath filter. When in doubt, consult manual or manufacturer
Avoid critical lengths

Centrifugal:

If a remote inlet filter is to be used, it is necessary to work closely with the supplier/manufacturer to size the inlet pipe. Because the centrifugal compressor is a “mass flow” type compressor, its overall performance is very dependent on identifiable and predictable inlet air pressure
Install drain leg on inlet line before the air enters the compressor

Discharge Piping

Rotary:

Pipe size should always be larger than unit connection size. Determine correct pipe size based on system flow, length of pipe, number of ends/valves, acceptable pressure drop, etc.
Pipe so condensate from air line cannot run back into unit
Support pipe so there is no strain at or on the compressor connection

Reciprocating:

Pipe size should be one or two sizes larger than compressor connection size. Never reduce discharge pipe size from connection size of unit. Check the pipe size for velocity and calculate pressure loss
Brace/Clamp pipe at regular intervals. DO NOT have pipe strain on compressor connection
Be sure you are not in “critical length” and, if you are, consult manual or manufacturer for proper corrective action
Use discharge pulsation bottles when possible on larger units

Centrifugal:

Refer to the manual/manufacture for detailed location of check valves, back valves, safety valves, etc

Discharge piping should be larger than the compressor connection and should have a smooth run directly away from the unit. It should not be too large, which can possibly create a “stonewall” type effect at the discharge

All turns should be “long sweep ells” to allow a minimum of backpressure. This is always recommended in any air system but it is much more critical in a mass flow centrifugal

All piping should slope away from the compressor. All risers should have drain legs. Install a drain leg immediately after the compressor in the discharge line

General Guidelines for All Piping

All air inlet and discharge pipes to and from the inlet and discharge connection of the air compressor must take into account vibration, pulsations, temperature exposure, maximum pressure exposed to, corrosion and chemical resistance, etc. In addition, lubricated compressors will always discharge some oil into the air stream, and compatibility of the discharge piping and other accessories (such as O-rings, seals, etc.) with both petroleum and/or synthetic lubricants is critical.

General Rules for Sizing Pipe in a Compressed Air Distribution System

Pressure drop between the compressor and point of use is irrecoverable
Pipe size should be large enough that pressure drop is held to a minimum or even nonexistent. There is no reason to tolerate any pressure loss during normal operation in the header distribution
Arrange piping to avoid the following types of strains:
- Strains due to dead weight of the pipe itself
- Strains due to expansion or contraction of the piping with temperature change
- Strains due to internal pressure within the piping
Design inlet and discharge piping for smooth flow with uniform translateral velocity over the entire area of the piping
Install a safety valve between the compressor and shut-off valve at 5 to 10 psi above compressor operating pressure. Never exceed the working pressure rating of any ASME vessel in the system
Plan for future emergencies and establish a tie in point to install a temporary compressor with power and aftercooler (if required)
Consider bypass lines or valves on all items that may require future maintenance
Use a loop design system if possible, both around the plant and within each production zone
Consider a second air receiver at end of the line or loop only if you have peak demands for air near that point
Locate outlets from the main header as close as possible to point of application. This helps limit large pressure drops through the hose
Outlets should always be taken from the top of the pipeline to alleviate carryover of condensed moisture to tools
All piping should be sloped so that it drains toward a drop leg moisture trap or receiver away from the compressor and/or process

Flexible connections should be used to reduce or absorb vibration and mitigate the effect of thermal expansion. They should not be used to correct misalignments. Any flex connection used should be investigated to be sure its specification fits the operating parameters of the system.

It is important to note that improper or incorrectly applied piping and material in an air system can result in mechanical failure, damage, and serious injury or death.

Compressor Piping Layout

Suction & Discharge Piping

Compressor Suction Piping Shall be as Short as Possible.
Compressor Suction Piping should have Inlet Filter / Strainer. It can be Temporary or Permanent
Suction Piping should be sloping/free draining towards Inlet Scrubber
Suction lines require a minimum straight run of piping upstream of the suction nozzle which varies between 3 and 8 times the normal pipe size. (Vendor requirement)
All operating valves must be readily accessible, preferably from grade.
All line to Compressor shall be provided with break-up flanges for Maintenance.
Compressor Suction Line Flowmeter: Suction routing shall be such that Upstream and Downstream straight length shall be sufficient for the performance of Flowmeter
Isometrics – Both Suction and Discharge piping should have noted for “Pickling and Passivation” i.e. Chemical cleaning of Lines before commissioning.
Anti-Surge Valve Is Designed and Supplied by Compressor Vendor.
Input to Compressor Vendor for Designing / Sizing the Anti-Surge Valve is given by piping, by providing suction and discharge length.
Anti-Surge Valve is located on Anti-Surge line which is basically a by-pass / recirculation line between Compressor Suction and Discharge Piping for Surge control
Anti-Surge Valve shall be located at Highest Point and shall be free draining on both side

Lube Oil Cooler & Piping

Lube Oil Cooler Shall be Accessible from Road.
Lube Oil Cooler Shall be located as close to Compressor as Possible.
Lube Oil Cooler Piping Should Not Interfere with Access and Maintenance space.
Lube Oil Cooler line must be Free Gravity flow requirements.
Lube Oil Cooler Piping Should have Break-up Flanges for Maintenance purpose.
Lube Oil Cooler Isometric should also have noted for “Pickling and Passivation” i.e. Chemical cleaning of Lines before commissioning.

Supporting of Compressor Piping

First support from Compressor Suction and Discharge nozzle is either Spring support or Adjustable support for Alignment during Construction / Erection.
Compressor piping should never be supported by the Compressor foundation. Pipe supports must be provided with independent foundations to avoid transmission of vibration.
Compressor Suction / Discharge Piping should be routed in such a way that it has enough flexibility to accommodate Thermal Expansion and to Reduce Nozzle Load.
Compressor Suction / Discharge Piping should be adequately supported as per Stress Engineers Support requirements.
Process Should be consulted for any possibility of two-phase flow/slug flow and the line should be supported accordingly
As compressors are meant for Gaseous fluid, the Hydro-test load on supports may be very high for big bore line. Hence we can recommend Temporary supports to be erected during Hydro-testing with the help of a Stress Engineer.