Piping Design (part 02)

Monday, June 29, 2009

While piping designer generate the routing in a plant, some aspect which effect to the piping performance have to be considered. A piping designer should have strong imagination about the condition in the plant while in operating process. For that, complete data as the predecessor should be available to support the designer start to create the routing.

The following items are what the piping designer should be use as their checklist.

1. Pipe specification, such as nominal pipe size (NPS), pipe's schedule, design temperature, and also the material specification.
2. Connection type for the opposite piping, is that weld connection, flange connection, or threaded connection. If weld connection, NPS under 2.5" should be in socket weld connection. For NPS above 2.5" should be in butt weld connection.
3. Still related with item#2 above, the designer should consider while there is a discrepancies with the pipe's wall thickness. ASME B16.25 should be refered to design how should the end of pipe to be machined.
4. Field weld connection should be considered due to the accessible of the spool of pipe to be installed in site. For example while the pipe penetrate a structural wall and fitted with expansion bellows. Then, a field weld connection should be provided to allow the expansion bellows installed in the penetration section.
5. Field weld connection also important to be provided, to allow adjusting the alignment of a very long spool of pipe in field.
6. To do the routing, the piping designer has to make sure that there isn't any clashes with other objects in field. The insulation thickness should be considered also as the outer size of pipes.
7. For piping with high thermal movement, it should be provided with expansion path. Although there are pipe supports that will guide the movement.
8. The designer has to make sure for the availability space for maintenance process. For example, the space to dismantle a strainer cover, as a strainer ussually installed to face the ground.
9. If there are valves or instruments those are installed on the piping, they should be accessible for operating and maintenance.
10. The routing should be placed much closer with any structural steel, to allow the pipe supports can be attached on the structural.
11. A transition material for a connection between high alloy pipe (P91 grade) with carbon steel pipe (SA-106) should be added, ussualy by using low alloy pipe (P22 grade).
12. Any welded attachment as a guidance of part of the supports should be shown in the isometric drawing clearly, completed with the coordinate location.

By considering the above items, any problem that usually comes while in erection stage can be avoided. The next part of this article will discuss about mechanically aspect in design process.