Pipelines and valves:Pipeline material,Hygiene and Hoses

Pipeline material

Although steel is the most commonly used pipeline material, many other materials are available to suit the conveyed material and the conveying duty. It was mentioned above that thin walled pipe would be easier to handle and erect because it is lighter. Aluminium pipe is often used for this purpose.

Hygiene

Due to the problems of moisture and condensation in pipelines there is always the possibility of steel rusting, and contaminating the conveyed material. In cases where hygiene is important, such as with many food and pharmaceutical products, the pipeline will need to be made from stainless steel.

Hoses

Where flexibility is required in a pipeline, and this cannot be conveniently achieved with a combination of straight pipe and bends, flexible hose can be used. Where a single line needs to feed into a number of alternative lines, and a flow diverter is not wanted to be used, a section of flexible hose of the steel braided type can be used to provide the link.

Where road and rail vehicles and boats need to be off-loaded, flexible rubber hose is ideal. It is available in natural rubber and a variety of synthetic materials come in a wide range of sizes. The author has conveyed various drilling mud powders through hoses at pressures of up to 6 bar gauge to obtain data for transferring these materials from boats to oil rig platforms in the North Sea. The author has also tested flexible hose compounded from steel and rated at 250 atm, for erosive wear resistance.

Flexibility is generally needed in ship off-loading applications with vacuum sys- tems, and hoses provide the necessary flexibility here. Care must be taken if the mater- ial is abrasive and has a large particle size, because the wear rate of rubbers can be excessive with such materials. Rubber hose is considered further in Section 5.4.

Erosive wear

If an abrasive material is to be conveyed in a pipeline, consideration must be given to the use of schedule 80 pipeline or higher. For very abrasive materials conventional mild steel pipeline is unlikely to be suitable, and spun alloy cast iron pipeline would be preferred. An alternative to this, which is commonly adopted, is to line a conventional steel pipeline with basalt.

If a more wear resistant material is required, then alumina ceramics can be used, but this is likely to be very much more expensive. A usual combination is to line the straight pipeline with basalt and to use alumina for the bends. Erosive wear of bends tends to be more severe than straight pipeline and so a much higher degree of protection needs to be given to them.

Material degradation

Friable materials need to be conveyed ‘gently’ and this is best achieved by controlling the conveying conditions. In terms of pipeline influences most of the problems of material degradation occur at the bends in the pipeline. It is the deceleration of particles on impact with bends that causes much of the damage. Decelerating forces are significantly lower with materials such as urethane and rubber, because of their resilience. It is generally a matter of compatibility with the conveyed product as to whether these materials can be incorporated into the pipeline. The subject of particle degradation is considered in some detail in Chapter 24.

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