For further information on this subject see ASME PTC-10, section 4.3
Piping arrangement should allow removal of temporary strainer without the need to dismantle piping, supports or affect alignments. Removable spool maybe used to facilitate this process.
Inter-stage and discharge piping should have sufficient flexibility under the thermal load resulting from the heat of compression.
A strainer should be installed in all compressor suction lines. All screens and filters should be sufficiently reinforced to prevent their failure and subsequent entry into the compressor. Strainers should be designed or selected to suit the service.
Unless otherwise specified by the compressor vendor, lines between knock-out pots and the compressor suction should be as short as practicable and preferably without pocket between the knock-out drum and compressor.
Suction lines taken from a header should preferably be connected to the top of that header. However, if the suction line is at least one pipe size smaller than the header, a center-line connection to the side of the header is accepted.
The anti-surge/recycle line should be sloped away from the anti-surge/recycle valve, which should be located at the highest point of the system.
Piping should be such arranged to not obstruct any operation, maintenance and mechanical handling requirements.
Exchangers should be arranged to facilitate operation and maintenance requirements, in particular cleaning requirements. The piping arrangements to each exchanger should generally be similar in arrangement.
Nozzles on exchangers should be positioned so that the best piping layout is obtained without affecting the design capacity of the equipment.
Piping should be arranged such that:
- On Shell & Tubes Heat Exchanger: It does not hamper removal of shell and channel covers and the withdrawal of the tube bundle.
- On Plate-Frame Heat Exchanger: It allows space to pull out the frame and replacement of the plates.
- On Printed Circuit Heat Exchanger: It allows space above the equipment for its entire replacement.
- On Air Coolers: It allows the replacement of the motor and belt without piping disconnection.
- On Electrical Heaters: It does not hamper removal of electrical head and the withdrawal of the tube bundle.
It may be necessary to provide a pipe spool, elbow, or other removable pipe piece between the block valve and the equipment nozzle.
Drain and vent nozzles on heat exchangers should be provided with valves and blind flanges.
Cooling water piping should be arranged such that coolers or condensers remain flooded in the event of loss of supply.
Piping should be arranged such that it does not does not hamper removal of WHRU bundle. It may be necessary to provide removable spools between the block valve and the WHRU connections to allow the maintenance.
Accesses to observation windows and instrument connections of the WHRU should be provided.
The piping designer should coordinate the piping requirements with the equipment designer to achieve optimum nozzles position and orientation.
For ease of operation and maintenance, vessels that are grouped together should have their platforms at the same elevation with interconnecting walkways. The number of stairways and/or ladders to the platforms should be determined in accordance with statutory regulations to meet safety requirements.
Vessels that are grouped together should, if practicable, be elevated such that their level gauges can be read from one common level.
Where possible, block valves should be located directly against the vessel nozzles. Piping should be arranged and supported such that spectacle blinds can be easily installed for maintenance purposes (vertical orientation) as shown on P&ID’s.
Elevation of manways on the top and bottom of vessels should be defined on a case by case basis. Manways should be orientated such that the manway cover opens away from access approach.
7. Vessels Trim
Vessel trim is defined as valves and piping components directly connected to a vessel, which do not form part of a piping line. Typically, vessel vents, drains, standpipes and various types of instrument connections.
Vessel trim design and materials are the responsibility of the piping section. A piping line number or numbers should be allocated for each vessel trim, and trim materials should be selected according to the designated piping class.
7.1 Level gauges
Level gauges are devices allowing visual observation of actual level through a glass plate or tube.
Depending on equipment design, level gauges can be either supplied as part of the equipment (not part of piping design) or mounted externally to the equipment and connected to the equipment (piping).
Level gauges should be placed in such a position that the level indicated will be visible from deck platform level or access ladder. The level in the gauge should be visible from the location where the same level is measured by another instrument.
Clearance should be provided for illuminators or back lighting when fitted.
7.2 Stand pipes
A stand pipe should be used when 2 or more Level gauges are requested in same area.
Stand pipes should be considered as part of the process piping and should be in accordance with the relevant piping class.
The minimum nominal size of the stand pipe should be 3” and the connection to the vessel should be 2” flanged connection.
Where level gauge standpipes are installed on equipment operating at elevated temperatures, flexibility should be provided considering differential expansion when isolation valves are closed.
8. Allowable Nozzle Loads
Forces and moments induced by piping on nozzles of equipment should not exceed the values stated in the various standards as specified in Piping Stress Analysis per Company standard.
For specific cases where such maximum allowable loads are not defined, the manufacturer’s standard requirements should be met.