PRODUCTS & EQUIPMENT
Materials used to manufacture pipes and their machinability
n an industrial setting, a material is never selected by chance. During the design phase, the characteristics of the materials must be carefully studied and determined in order to avoid subsequent complications when in use, and to avoiding incurring unnecessary costs. This is especially the case when
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choosing a material to be used in a pipe. This is because some pipes are subjected to considerable mechanical, thermal or chemical stresses, depending on the type of fluid they convey, with pressure and temperature playing a determining role. The material used to manufacture
the pipe has an influence on all the manufacturing operations, including machining. The machinability of the pipe depends directly on the material used to manufacture the pipe, and for each given material, specific precautions must be taken in order to ensure high quality machining. Machining is a common operation
when preparing a piece for welding. The pipe end has to be machined at specific angles so that the weld can penetrate the entire thickness of the pipe material.
Standard steel Standard steel pipes are the most commonly used types of pipes owing to their low cost and mechanical properties which make them suitable for a wide range of applications. Steel pipes are resistant to mechanical stresses, durable and formable. This means that they can be used for applications with significant temperature or pressure variations. Standard steel pipes are also very commonly used in situations where impacts or vibrations can affect the pipeline (underneath roads, for example). In addition, steel pipes are fairly easy to manufacture, bend and cut.
8 IMT June 2016 1. Machining a thick pipe prior to welding with a PROTEM US 150HSB beveling machine Steel pipes are, however, very
prone to corrosion if no preventive treatment is applied. Galvanization is a common corrosion-control treatment; this consists of applying a zinc coat to the steel pipe. This coating then oxidizes in the place of the steel which it protects, with the all-important difference, however, being that the zinc oxidizes very slowly.
Low-alloy steel (i.e., with a low
carbon level between 0.008% and 2.14%) can be easily machined. When the carbon rate increases, the material properties (such as hardness or mechanical resistance) tend to improve significantly. However, machining steels with a high carbon level is more difficult.
P91 Steel P91 steel is an alloy steel with a high chromium (9%) and molybdenum (1%) content. Adding chromium increases the mechanical resistance at high temperatures as well as corrosion
resistance, and adding molybdenum improves creep resistance. Small amounts of nickel and manganese are added to enhance the overall hardness of the material. P91 steel is very sensitive to changes in its microstructure that can occur during excessive heating. These microstructure variations tend to weaken the material. This is why
cold machining is often preferred for cutting this material. P91 was initially developed for
the manufacturing of pipelines in conventional or nuclear thermal power plants, where the steam leaves the superheater of a boiler in a modern conventional/thermal plant at a temperature of between 570°C to 600°C and a pressure of 170
Machining a pipe at an angle of 30° with a PROTEM US 25 beveling machine
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