Insulation Support Lug...

Friday, July 31, 2009

As a high temperature fluid transporter, piping shall be insulated. It can be a mineral fiber insulation, or ceramic fiber insulation, depend on the temperature characteristic. There are two type of pipe insulation, blanket type and preformed type. Each type has strenghtness and weakness. In this article, i'd like to explain about how the insulations attached on the pipe, regarding with their strenghtness and weakness.


The first type of pipe insulation is blanket type. Actually, this type can be directly attached to the pipe as long as the pipe orientation is horizontal. But, if the pipe orientation is vertical, then the pipe should be completed with insulation support lug to avoid the insulation will shagging.
It shall shop welded with the same material of the pipe. The thickness is around 1/16", so while the material is alloy, it is allowed to ignore the PWHT. Insulation support lug is needed only for a 6" NPS or larger and attached at every 6' elevation. The width is 2" and the length shall extend to reach 1" penetrating the 2nd layer of insulation. In every elevation, insulation support lug quantity are four at each quadrant of the pipe.
The alternative for this insulation lug is called Marman clamp that can be attached in field, without any welding work. This clamp will be discussed in the next article.
The second type of insulation is preformed type, while insulation support lug is not required.

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.

Piping Design (part 01)

First of all, i'd like to make a clear understanding in determining between pipeline and piping. Pipeline has long distance in transporting fluids, it can be a hundreds miles away from the upstream to downstream. Meanwhile, piping just to transport the fluids in a short distance within the plant area. Pipeline used to be has large bore of nominal pipe size, above 20". meanwhile piping has smaller bore of nominal pipe size, under 18".
Now we've understood the main discrepancies between pipeline and piping, since i'd like to discuss about the design process for piping only, in the next paragraph.

Many aspects should be considered while design a piping system. As we've discussed in previous article, regarding the discrepancy between pipeline and piping. So, in this article we talk about piping design consideration, instead of pipeline. Although the items to be considered are mostly same, but i'd like to focus in piping.
In design stage, there are three main aspect which cover the overall detail aspects. The first aspect is related with the piping system's performance to transport the fluids. Based on "Inspeksi Teknik-Buku3" wrote by Sri Widharto, the parameters should be considered are as follow :

* Design temperature, is the temperature of pipe's material which is simulated in the most critical condition. In this case, critical condition means a condition that demand the maximum specification of the piping's material, including it's fittings. I divide the piping for two condition, un-insulated and insulated.

1. For un-insulated piping system, if the fluid temperature <>= 100 deg F (38 deg C), then the piping system's temperature (including the valves, flat face flange, welded joint fittings, and other components which have equal rating with the pipe's wall thickness, may not less then 95% of fluid's temperature. For flange's temperature (unless flat face flange) may not less then 90% of fluid's temperature. And for the fastener's temperature may not less then 80% of fluid's temperature.
2. For an insulated piping system, the piping system's temperature is designed to be equal with the fluid's temperature. Unless, based on previous experienced operation that make the design temperature should be considered to follow the existing data.

* Design pressure, is the pressure which may not less then a combined pressure from internal and external pressure in maximum and or minimum temperature which may occur in operating condition. A design pressure have to be able to throw out an over pressure that could be occur while in operating condition. Over pressure caused by a fluctuative pressure, incorrect operating, or even failure of equipment's function. Therefore, a pressure relieving device always installed in a piping system.

That is all i can describe about design process for piping system which is related with it's performance. We are going to have a long discussion regarding with design process related with the piping routing and mechanically consideration, in the next part of this article