Mechanical Abuse

The marine environment is highly aggressive. Materials in marine service are constantly exposed to water, corrosive salts, strong sunlight, extremes in temperature, mechanical abuse, and chemical pollution in ports. This climate is very severe on ships, buoys, and navigational aids, offshore stmctures such as drilling platforms, and faciUties near the shore such as piers, locks, and bridges. 

One early program carried out at AUied-Signal, Inc. proposed the use of conductive polymers in remotely readable indicators (210). Conductivity changes induced in the conductive polymer could be read externally and the history of the sample known. Systems designed to detect time—temperature, temperature limit, radiation dosage, mechanical abuse, and chemical exposure were developed. 

Plastic Materials In comparison with metalhc materials, the use of plastics is limited to relatively moderate temperatures and pressures [230°C (450°F) is considered high for plastics]. Plastics are also less resistant to mechanical abuse and have nigh expansion rates, low strengths (thermoplastics), and onlv fair resistance to solvents. However, they are lightweight, are good thermal and elec trical insiilators, are easy to fabricate and install, and have low fric tion factors. 

Hermetically sealed electrical devices must be verified by a testing laboratory to meet mechanical abuse and to withstand aging and exposure to expected chemicals. Devices potted with common silicones and similar materials by an end user or even a manufacturer, without testing, and devices merely provided with O-rings seldom meet acceptable criteria. Normally, hermetically sealed devices must be sealed through metal-to-metal or glass-to-metal fusion. Many electrical relays, switches, and sensors are available as hermetically sealed devices for common oil and gas producing facility applications. Hermetically sealed devices are often desirable to protect electrical contacts from exposure to salt air and other contaminants. 

As with tissue, woven glass cloth is used for decorative or acoustic purposes. Additionally, close-woven fabrics give improved fire-safety properties and are resistant to mechanical abuse. Glass cloth or scrim of an extremely open weave is used on insulants as a key for mastic or hard-setting finishes. 

The fluoroacrylic polymers are high-modulus, low-elongation plastics, which are brittle in the sense that all thermosetting polymers are brittle. However, they are tough, rugged materials not easily damaged by impact or mechanical abuse. 

Visually check for the loss of fireproofing materials as a result of mechanical abuse. 

Chemically resistant masonry structures are composed of three independent parts supporting structure, membrane fluid stop, and inner lining to protect the membrane from thermal and mechanical abuse. These three parts are essential to any economically satisfactory chemically resistant structure. This does not mean that the three functions may always require three distinct materials. The three functions may be accomplished by two materials, or even a single one. 

In tanks where brick wall linings may not be desired, brick floors are sometimes installed in the bottoms to protect the bottoms (and perhaps the bag liner) from steam jets, mechanical abuse and the like. (Canadian Chemical Processing for September 3, 1980, Page 21, provides a case history of three rectangular creosoted Douglas Fir tanks, with 316 stainless tie rods, installed in 1958, and apparently still used by the purchaser at the date of publication for acid/sul-furic cleaning of copper and brass bars up to 50 feet in length. The units are lead-lined, with "acid brick" laid over the lead in the tank bottoms.)... 

Over the past century, techniques have been developed to fire on metal surfaces, glass and porcelain in suitable formulations and in adequate thicknesses to be a liquid-tight barrier to protect the substrate from chemical attack by contained liquids. In such composite structures, the glass is better able to withstand thermal and mild mechanical abuse. Reactors made in such a manner have given long economical service over the years, and have been manufactured in sizes larger than they could have been if made entirely from glass. 

Carbon bricks are used in chemical-resistant construction in exposures which cannot readily be handled by other kinds of brick. Inasmuch as their cost is nearly 10 times that of shale or fireclay, and they provide not nearly as much insulation nor resistance to mechanical abuse, their selection is dictated by only the most compelling reasons. These reasons may be divided into four categories ... 

In process vessels, the foamed glass block can be substituted for several courses of acid brick. A brick facing over the block serves both to protect the block against abrasion from mechanical abuse and to lower the temperature at the face of the block when operating temperatures exceed the limits of the block. In both cases, the block installed over a membrane and beneath brick re-... 

A piece of rubber lined equipment at the end of its service life is re-lined if the metal is not badly damaged due to mechanical abuse or/and spillover of acids and so on. For re-lining the remnants of rubber sticking to the metal surface are removed by hot water or steam with chemical additives before sand blasting is done. 

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