Chemical compatibility

Chemical compatibility is another important factor to reckon with in material selection as in the case of butterfly valves which are frequently used in industrial fluid flow systems where the valves are operated to load and unload different kinds of fluids for shipment or storage. These applications include tank trailers for transportation of fluids from one location to another as well as fluid flow pipelines. A typical butterfly valve usually incorporates a resilient rubber seal component which the valve pivots to seal off the flow lines and when opened allows the fluid to be conveyed to the flow line. The chemicals transported in tanks using butterfly valves are often caustic or acidic. These chemicals corrode the pivot area of the valve making its function ineffective. The rubber gasket material prevents leakage while the valve chamber is protected by a chemically resistant rubber material. 

Rubber manufacturers develop their own rubber compounds suitable for constructing chemical plants and equipment possessing the chemical and physical properties to match the functional 

The use of materials for design of connections that are mutually incompatible by reason of then-chemical contents under particular environmental conditions, e.g. vulcanized rubber, which contains sulphur, affecting metal in contact, etc. should be avoided. 

Materials that, under ambient conditions or when under fire or in high-temperature conditions, out-gas or liberate corrosive fumes in the proximity of vulnerable materials that can be adversely affected by such fumes and their functional stability impaired should not be used  

Where phenolic insulating materials, varnishes or encapsulating compounds must be used in electrical or electronic equipment, and these are subject to elevated temperatures in enclosed spaces, cadmium- or zinc-plated components should be avoided. 

Contact between strength materials and any auxiliary materials, compounds, wood or textiles, which by leaching of any contained chemical corrosive on to the surfaces of the strength materials, can materially reduce the functional strength of these critical structures or components are also best avoided  

The use of galvanized fasteners in contact with stainless steel structures or components subject to temperatures in excess of the melting temperature of the zinc, etc. is not recommended. 

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Table 11. Chemical Compatibility of Fibers in Dust Collector Bags...

Polymers used for seat and plug seals and internal static seals include PTFE (polytetrafluoroeth ene) and other fluorocarbons, polyethylene, nylon, polyether-ether-ketone, and acetal. Fluorocarbons are often carbon or glass-filled to improve mechanical properties and heat resistance. Temperature and chemical compatibility with the process fluid are the key selec tion criteria. Polymer-lined bearings and guides are used to decrease fric tion, which lessens dead band and reduces actuator force requirements. See Sec. 28, Materials of Construction, for properties. 

Chemical incompatibility charts can help in organizing available data on the incompatibilities existing between expected mixtures. Frurip (Frurip et ah, 1997) gives one procedure for developing a chemical compatibility chart while describing some of the tools available. CCPS G-13 also provides a table of known incompatibility hazards. 

Erurip, D. J., T. C. Elofelich, D. J. Eeggett, J. J. Kurland, and J. K. Niemeier, 1997. A Review of Chemical Compatibility Issues, Proceedings of the Annual Loss Prevention Symposium, American Institute of Chemical Engineers, Vol. 31, 1997. 

Chemical compatibility chart (How do the chemicals involved react with each other if one is added m excess or the addition of one is limited how do these chemicals react with common metals and chemicals )... 

CELLULOSE - As fibrous precoat aids or where special chemical compatibilities are required cellulosebased additives achieves separations that would otherwise be diffiicult or impossible. 

The chemical resistance of PTFE is almost universal It resists attack by aqua regia, hot fummg nitnc acid, hot caustic, chlorine, chlorosulfonic acid, and all solvents. Despite this broad chemical resistance, PTFE is attacked by molten alkali metals, ammonia solutions of such metals, chlorine trifluoride, and gaseous fluonne at elevated temperature and pressure PTFE swells or dissolves m certam highly fluonnated oils near its melting point. Specific lists of chemicals compatible with PTFE are available [/.8]... 

Improve electrolyte material, using better conductors that are still chemically compatible with the electrodes. 

Galvanic corrosion reports have emerged from two sources. In the first , the chemical compatibility of uranium carbides and Cr-Fe-Ni alloys was discussed. Evaluation was by thermodynamic modelling and experimental... 

In all circumstances it is important to ensure that the inhibitor is chemically compatible with the liquid to which it is added. Chromates, for example, cannot be used in glycol antifreeze solutions since oxidation of glycol by chromate will reduce this to the trivalent state which has no inhibitive properties. 

Overmolding is the process by which two different materials are joined into one assembly without using secondary operations like gluing or welding. In case the materials are chemically compatible, chemical bonds may form between them and so mechanical interlocks are not required. There are two common techniques of overmolding—insert molding and multiple-shot injection molding. 

The choice of a particular inactive ingredient and its concentration is based not only on physical and chemical compatibility, but also on biocompatibility with the sensitive and delicate ocular tissues. Because of the latter requirement, the use of inactive ingredients is greatly restricted in ophthalmic dosage forms. 

The performance should be evaluated in terms of drug and component physical and chemical compatibilities. Particle size and emitted dose determinations are required. Through-life performance should be evaluated as this is a multidosing reservoir system. The influence of temperature and humidity on stability and performance of the product should also be considered. 

The primary characteristic necessary for a liner, cover, or cutoff wall is low permeability, which essentially enables them to slow down the seepage or diffusion of chemicals. Clay is therefore the main material used to construct these containment systems. The thickness and chemical compatibility of containment systems are of concern in assessing the performance of a system. For example, clay liners are constructed as a simple liner that is 2 to 5 ft thick. In composite and double liners, the compacted clay layers are usually between 2 and 5 ft thick, depending on the characteristics of the underlying geology and the type of liner to be installed. Regulations specify that the clay used can only allow water to penetrate at a rate of less than 1.2 in./yr. However, the effectiveness of clay liners can be reduced by fractures induced by freeze-thaw cycles, drying out, and the presence of some chemicals. 

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