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Piping

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From 01/29/2015 through 2/5/2013

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Notes

2. “Within industry, piping is a system of pipes used to convey fluids (liquids and gases) from one location to another. The engineering discipline of piping design studies the efficient transport of fluid.

Industrial process piping (and accompanying in-line components) can be manufactured from wood, fiberglass, glass, steel, aluminum, plastic, copper, and concrete. The in-line components, known as fittings, valves, and other devices, typically sense and control the pressure, flow rate and temperature of the transmitted fluid, and usually are included in the field of Piping Design (or Piping Engineering). Piping systems are documented in piping and instrumentation diagrams (P&IDs). If necessary, pipes can be cleaned by the tube cleaning process.

"Piping" sometimes refers to Piping Design, the detailed specification of the physical piping layout within a process plant or commercial building. In earlier days, this was sometimes called Drafting, Technical drawing, Engineering Drawing, and Design but is today commonly performed by Designers who have learned to use automated Computer Aided Drawing / Computer Aided Design (CAD) software.

Plumbing is a piping system that most people are familiar with, as it constitutes the form of fluid transportation that is used to provide potable water and fuels to their homes and business. Plumbing pipes also remove waste in the form of sewage, and allow venting of sewage gases to the outdoors. Fire sprinkler systems also use piping, and may transport nonpotable or potable water, or other fire-suppression fluids.

Piping also has many other industrial applications, which are crucial for moving raw and semi-processed fluids for refining into more useful products. Some of the more exotic materials of construction are Inconel, titanium, chrome-moly and various other steel alloys.”

(Wikipedia, Piping, 5/10/2012)

1. Polyethylene materials are often used for pipes in which the base resin consists of  two polyethylene fractions with different molecular weights.  Such blends are bimodal or multimodal. Such polyethylene compositions are frequently used e.g. for the production of pipes due to their favourable physical and chemical properties as e.g. mechanical strength, corrosion resistance and long-term stability.  When considering that the fluids, such as water or natural gas, transported in a pipe often are pressurized and have varying temperatures, usually within a range of 0 to 50 C., it is obvious that the polyethylene composition used for pipes must meet demanding requirements. On the other hand, to facilitate installation of the pipes in the ground requires flexibility.

Polyethylene materials for piping should have high mechanical strength, good long-term stability, notch/creep resistance and crack propagation resistance, and, at the same time high flexibility. However, at least some of these properties are contrary to each other so that it is difficult to provide a composition for pipes which excels in all of these properties simultaneously. For example, stiffness imparting mechanical strength to the pipe is known to improve with higher density but, in contrast, flexibility and notch/creep resistance is known to improve with reduced density.

Furthermore, as polymer pipes generally are manufactured by extrusion, or, to a smaller extent, by injection moulding, the polyethylene composition also must have good processability.

It is known that in order to comply with the contrary requirements for a pipe material, bimodal polyethylene compositions may be used. Such compositions are described e.g. in EP 0 739 937 and WO 02/102891. The bimodal polyethylene compositions described in these documents usually comprise two polyethylene fractions, wherein one of these two fractions has a lower molecular weight than the other fraction and is preferably a homopolymer, the other fraction with higher molecular weight preferably being an ethylene copolymer comprising one or more alpha-olefin comonomers.

(Bachman et al, US Patent 8,367,763, 2/5/2013

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Roger D. Corneliussen
Editor
www.maropolymeronline.com

Maro Polymer Links
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Copyright 2012 by Roger D. Corneliussen.
No part of this transmission is to be duplicated in any manner or forwarded by electronic mail without the express written permission of Roger D. Corneliussen
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* Date of latest addition; date of first entry is 5/10/2012.

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