o The design should avoid crevices and corners where moisture may become

O the design should avoid crevices and corners where

This preview shows page 10 - 11 out of 73 pages.

o The design should avoid crevices and corners where moisture may become trapped, and adequate ventilation and drainage should be provided. o The design should allow for any washing down and cleaning. o Joints which are not continuously welded should be sealed, for example, by the use of mastic compounds or impregnated tapes. o Where dissimilar metals have to be joined, high-strength epoxy adhesives should be considered since they insulate the metals from each other and prevent galvanic corrosion. o Materials which are inherently corrosion resistant should be chosen or, if this is not possible, an anti- corrosive treatment should be specified. (II) COMPOSITION AND STRUCTURE The presence of impurities in non-ferrous metals reduces their corrosion resistance. Hence the high level of corrosion resistance exhibited by high-purity copper, aluminium and zinc. The importance of grain structure has also been mentioned above, and a fine-grain structure is generally less susceptible to corrosion than a coarse-grain structure. The inclusion of certain alloying elements such as nickel and chromium can also improve corrosion resistance, for example, the stainless steels and the cupro-nickel alloys. (III) ENVIRONMENT The environment in which the component or assembly is to spend its service life must be carefully studied so that the materials chosen, or the anti-corrosion treatment specified, will provide an adequate service life at a reasonable cost. It would be unnecessary and uneconomical to provide a piece of office equipment which will be used indoors with a protective finish suitable for heavy-duty contractors plant which is going to work on construction sites in all kinds of weather conditions. (IV) APPLIED OR INTERNAL STRESSES Chemical and electrochemical corrosion is intensified when a metal is under stress. This applies equally to externally applied and internal stresses, although more common in the latter case. Internal stresses are usually caused by cold-working and, if not removed by stress-relief heat treatment, results in corrosive attack along the crystal boundaries. This weakens the metal considerably more than simple surface corrosion. An example of intercrystalline corrosion is the ‘season cracking’ of a brass after severe cold-working. Intercrystalline corrosion occurs at the grain boundaries of crystals not only when impurities are present but also when stress concentrations are present. Grain boundaries are regions of high energy levels, even in very pure metals, so corrosion tends to occur more quickly at grain boundaries. Severely cold-worked α-brasses are prone to ‘season cracking’. Here, intercrystalline corrosion follows the grain boundaries until the component is no longer able to sustain the internal stresses due to cold-working.
Image of page 10
Image of page 11

You've reached the end of your free preview.

Want to read all 73 pages?

  • Fall '19

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern

Stuck? We have tutors online 24/7 who can help you get unstuck.
A+ icon
Ask Expert Tutors You can ask You can ask You can ask (will expire )
Answers in as fast as 15 minutes
A+ icon
Ask Expert Tutors