Selection for corrosion resistance

In order to select the correct material of construction, the process environment to which the material will be exposed must be clearly defined. Additional to the main corrosive chemicals present, the following factors must be considered  

Temperature-affects corrosion rate and mechanical properties. 

The conditions that may arise during abnormal operation, such as at start-up and shutdown, must be considered, in addition to normal, steady state, operation. 

The resistance of some commonly used materials to a range of chemicals is shown in Appendix C. More comprehensive corrosion data, covering most of the materials used in the construction of process plant, in a wide range of corrosive media, are given by, Rabald (1968), NACE (1974), Hamner (1974), Perry el al. (1997) and Schweitzer (1976) (1989) (1998). 

The twelve volume Dechema Corrosion Handbook is an extensive guide to the interaction of corrosive media with materials, Dechema (1987). 

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Materials selection for corrosion resistance is as reliable as the information upon which it is based. Corrosion information derives from two sources— experience or test results. 

Table 4 Organic coatings selected for corrosion resistance in various environments...

There are no films or protective surface films on active metals, e.g., mild steel in acid or saline solutions. Passive metals are protected by dense, less readily soluble surface films (see Section 2.3.1.2). These include, for example, high-alloy Cr steels and NiCr alloys as well as A1 and Ti in neutral solutions. Selective corrosion of alloys is largely a result of local concentration differences of alloying elements which are important for corrosion resistance e.g., Cr [4],... 

Selection of Corrosion-Resistant Materials The concentrated sofutions of acids, alkalies, or salts, salt melts, and the like used as electrolytes in reactors as a rule are highly corrosive, particularly so at elevated temperatures. Hence, the design materials, both metallic and nonmetallic, should have a sufficiently high corrosion and chemical resistance. Low-alloy steels are a universal structural material for reactors with alkaline solutions, whereas for reactors with acidic solutions, high-alloy steels and other expensive materials must be used. Polymers, including highly stable fluoropolymers such as PTFE, become more and more common as structural materials for reactors. Corrosion problems are of particular importance, of course, when materials for nonconsumable electrodes (and especially anodes) are selected, which must be sufficiently stable and at the same time catalytically active. 

In addition to the active design principles for reducing the risk of sulfide problems, a number of more passive principles exist. The following design considerations are especially relevant for the reduction of corrosion selection of corrosion-resistant materials and design of a well-ventilated sewer system. 

The squeezing apparatus described here is the one in use at the British Geological Survey (BGS) and utilizes a hydraulic pump (Wykeham Farrance Engineering Ltd., Slough) which has a maximum output stress of 70 MPa and hydraulic hoses and fittings (Fig. 10.9). The main body of the cell and other metal parts in contact with the test sample or pore water are manufactured from Type 316 stainless steel, selected for its resistance to corrosion and its high tensile strength. 

Selection of corrosion-resistant materials and development of the concept for key components such as the H2SO4 vaporizer. 

Gupta, Materials Selection for Corrosion Control, ASM International, Materials Park, OH, 1993. (d) P. Schweizer, Corrosion-Resistant Piping Systems, Dekker, New York,... 

The choice of a material for a plant component is not only decided by requirements for corrosion resistance, but also depends on process parameters (T, P, concentration, pH, state of flow, etc.) and product specifications. Apart from economy and good workability, there are a wide range of factors that must be taken into account in materials selection. 

W.T. Bryan, Selection of alloys for corrosion-resistant service. Met. Prog. 74 (1958) 102—105. 

The most important methods for preventing atmospheric corrosion are 1) to select a corrosion-resistant structural material, 2) to use a corrosion-resistant coating (metallic, inorganic, organic or composite), and 3) to close internal cavities in order to avoid access of humid air, or conversely, 4) to make sure that there is ample ventilation and drainage, and possibly 5) to supply oil, grease, or special substances such as tectyle to the cavities. 

FIGURE 9.9 Austenitic and duplex stainless-steel grades and their yield strength (Rpo2) and corrosion resistance. (From B. D. Craig. Selection guidelines for corrosion resistant alloys in oil and gas industry. In Materials Selection for Oil and Gas Industry, www.stainless-steel-world.net/pdf/10073.pdf. With permission.)... 

Also, in selecting materials for the construction of cells it must be remembered that the concentrated electrolyte solutions used for electrolysis are corrosive and even pumps, pipework and cell bodies must be selected with corrosion resistance in mind. 

For all professionals involved in design and maintenance processes, this book should serve as a valuable aid in the selection of corrosion-resistant linings and coatings. 

CBR systems is presented in Fig. 12. The first, "M-BASE," facilitates the process of retrieving materials according to a given set of desired properties and/or specifications. The second, "C-BASE, helps the materials engineer in the difficult task of selecting materials for corrosion resistance in complex chemical environments. 

The results of extensive corrosion testing, biocompatibility studies, and clinical evaluation have been used to select the corrosion-resistant metals and alloys that are in use as implants today. In addition, there are new materials being introduced as well as modifications of the currently used ones. Additional information on the biological and chemical reactions at the body/biomaterial interface would be useful in determining short- and long-term effects on the body and in pref>aring the biomaterial for its intended use. 

Also, in selecting materials for theconstniction of cells it must be remembered that the concentrated electrolyte solutions used for electrolysis arc corrosive and even pumps, pipework and cell bodies must be selected with oorrosiotl resistance in mind. Indeed, whenever it is feasible, non-eleciroda components should be fabricated from (or coated with) an electrically insulating material (usually a polymer but possibly a ceramic), in particular it is wise to avoid the problem of bipolar MTodon (Chapter 0) which may arise if a conductive material interrupts the usual current path between anode and cathode It is essential to test all components in the system for corrosion resistance, with the cell on load and under open-ciTCuit conditions ... 

The selection of corrosion-resistant alloys for service in multi-oxidant atmospheres of high Pq is based primarily on oxidation resistance and, specifically, on the tendency of the alloy to form a Cr203-, Si02-, or Al203-rich scale. Although this is true for I0W-P02 atmospheres also, as will be discussed in the following sections, the base-metal and specific alloying elements play... 

The most common experiments for the evaluation and selection of corrosion-resistant materials focus on the variation of the mass according to the length of exposure to the aggressive atmosphere, which is determined through the equation ... 

Some particular requirements and typical selection considerations are presented in Table 11.2. The material selection process is also influenced by the fact that the materials are either considered for the construction of a new system, or for the modification or repairs in an existing facility. For the construction of new equipment, the selection procedure should begin as soon as possible and definitively much before the design is finalized since the optimum design for corrosion resistance may greatly affect how the system will be assembled or constructed. 

In this paper deterministic-probabilistic structural integrity analysis will be made for the pipe section with the movable support. As the movable support has unfavorable conditions for corrosion resistance high corrosion rates will be used in this paper. To select pipe section with movable support the statistical analysis of pipe failures and structural integrity analysis of pipelines were made. According to the statistical analysis results, three main pipelines 5K, 3Z and 5T were determined as... 

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