Liners chemical resistance

In the sheeting market, the low density polyethylenes are less important than the high density resins. The high density resins have excellent chemical resistance, stress-crack resistance, durabiUty, and low temperature properties which make them ideal for pond liners, waste treatment faciUties, and landfills. In thicker section, HMW-HDPE sheet makes good containers, trays, tmck-bed liners, disposable items, and concrete molds. The good durabiUty, abrasion resistance, and light weight are critical elements for its selection. 

The principal uses of PCTFE plastics remain in the areas of aeronautical and space, electrical/electronics, cryogenic, chemical, and medical instmmentation industries. AppHcations include chemically resistant electrical insulation and components cryogenic seals, gaskets, valve seats (56,57) and liners instmment parts for medical and chemical equipment (58), and medical packaging fiber optic appHcations (see Fiber optics) seals for the petrochemical /oil industry and electrodes, sample containers, and column packing in analytical chemistry and equipment (59). 

The thermal stabiUty of epoxy phenol—novolak resins is useful in adhesives, stmctural and electrical laminates, coatings, castings, and encapsulations for elevated temperature service (Table 3). Filament-wound pipe and storage tanks, liners for pumps and other chemical process equipment, and corrosion-resistant coatings are typical appHcations using the chemically resistant properties of epoxy novolak resins. 

Powder Costings. Epoxy-based powder coatings exhibit useful properties such as exceUent adhesion, abrasion resistance, hardness, and chemical resistance. The appHcation possibUities are diverse, including refrigerator liners, oU filters, hospital equipment, primers, shelving, automobUe springs, and fire extinguishers. 

Concrete and fiberglass vaults are often used, although they can be subject to environmentally induced cracks. Soil and clay liners are not allowed. Flexible hner systems have been developed that may be a cost-effective and environmentally sound alternative. State-of-the-art liner technology has overcome many of the previous problems with seams, low mechanical strength, and chemical resistance. 

This section discusses chemical compatibility (resistance) of geosynthetic and natural liner materials with wastes and leachates. Even in a relatively inert environment, certain materials deteriorate over time when exposed to chemicals contained in both hazardous and nonhazardous leachate. It is important to anticipate the kind and quality of the leachate a site will generate and select liner materials accordingly. The chemical resistance of any FML materials, geonets, geotextiles, and pipe should be evaluated before installation.39... 

Furthermore, a cell header with its 70-100 connections is not easy to replace, and considerable numbers of safety features have to be incorporated into its design. Composite materials do not lend themselves to effective non-destructive testing and a leaking joint may lead to delamination of the chemical-resistant liner from its mechanical support. Since any leaks cannot be detected easily in such circumstances, the entire header must be replaced with a corresponding electrolyser downtime. 

The principal test to establish the chemical resistance of the polymeric landfill liners to liquid wastes and industrial effluents is the immersion of geomembrane in a sample either of a defined chemical mixture or of a leachate from an existing storage site. This is performed either at various elevated temperatures in order to generate an Arrhenius diagram, or at fixed temperatures of 50 °C and at 20 °C, and is followed by a number of, primarily, mechanical evaluation tests. 

Liner types available are suitable for a wide variety of chemical services, including acids, alkalies, and various solvents. All liners are permeable to some degree, and manufacturers use various methods to vent gas out of the interspace between the liner and casing. All plastics are subject to environmental stress cracking (ESC). ESC can occur even when the liner is chemically resistant to the service. Lined pipe manufacturers should always be consulted regarding liner selections and service apph-cations. Also consult manufacturers regarding vacuum service limits. 

Since EPDM rubber is costly and the price fluctuates widely, high filler and oil loadings are resorted to, to achieve relatively low cost compounds. But these compounds tend to have poor strength and abrasion resistance. High quality stocks, especially those with peroxide cures, are considerably more expensive than NR, BR or SBR stocks. EPDM is used in belts and hoses meant for conveying hot materials because of its excellent heat resistance. Its excellent chemical resistance makes it a preferred rubber for specialty belts, chemical hoses and pump liners. 

The following Chemical Resistance Table is based on the use of hot asphalt as a membrane when used with a chemically-resistant masonry inner liner. It is derived from a number of sources and the author cannot assume responsibility for its accuracy. 

Installed alone as a semi-refractory material, the foamed borosilicate glass block lining withstands hot face temperatures up to 960°F. It may also be used with refractory, chemical-resistant masonry or monolithic internal linings at temperatures above 960°F providing a unique combination of corrosion protection and heat conservation with little added weight and a lesser overall lining thickness. The foamed glass block may also be fabricated into nozzles, T-sec-tions, elbows, liner inserts and other custom shapes. 

Properties of fluoropolymers that have led to applications include chemical resistance, thermal stability, cryogenic properties, low coefficient of friction, low surface energy, low dielectric constant, high volume and surface resistivity, and flame resistance. Fluoropolymers are used as liners (process surface) because of their resistance to chemical attack. They provide durable, low maintenance and economical alternatives to exotic metals for use at high temperatures without introducing impurities. Electrical properties make fluoropolymers highly valuable in electronic and electrical applications as insulation, e.g., FEP in data communications. 

Chemical Processing Chemical resistance Good mechanical properties Thermal stability Cryogenic properties Gaskets, vessel liners, valve and pipe liners, tubing, coatings... 

The valve had a PFA liner, which was the appropriate material for this application from a chemical resistance standpoint. A close-up picture of the interior surface ofthe valve is seen in Fig. 10.37. One of... 

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