Static interference (or steady state interference) is the most common type of interference corrosion control personnel normally encounter. The tasks/skills are further reinforced via classroom training and hands-on training/experience. The basic skills of interference testing are normally passed on from senior field personnel to entry level personnel. Interference testing is one of the skills that is learned through education and experience. This paper will discuss interference testing and present some case histories of basic static interference situations and the mitigation methods used. NACE International assumes no responsibility for the interpretation or use of this standard by other parties and accepts responsibility for only those official NACE International interpretations issued by NACE International in accordance with its governing procedures and policies which preclude the issuance of interpretations by individual volunteers.Interference Testing is a task learned through education and experience and is one of the basic skills of Cathodic Protection Personnel. Unpredictable circumstances may negate the usefulness of this standard in specific instances. Neither is this standard intended to apply in all cases relating to the subject. This standard represents minimum requirements and should in no way be interpreted as a restriction on the use of better procedures or materials. Nothing contained in this NACE International standard is to be construed as granting any right, by implication or otherwise, to manufacture, sell, or use in connection with any method, apparatus, or product covered by Letters Patent, or as indemnifying or protecting anyone against liability for infringement of Letters Patent.
Its acceptance does not in any respect preclude anyone, whether he or she has adopted the standard or not, from manufacturing, marketing, purchasing, or using products, processes, or procedures not in conformance with this standard. This NACE International standard represents a consensus of those individual members who have reviewed this document, its scope, and provisions. These alloys are readily polarized, and galvanic effects on other, less noble metals and alloys tend to be minimized. In chloride bearing solutions, Alloy 600 is reported to occupy two positions because of the existence of active and passive states similar to the stainless steels. With the chromium nickel alloys, the combination of a passive surface with the inherent resistance of the nickel based alloys (e.g., Alloys 600, 625, C276) places them in more noble positions in the traditional galvanic series.
In some environments, the cast structure of a nickel weld may be anodic to the parent metal. Nickel and its alloys are similar to copper alloys in their effects on stainless steels. In chloride bearing solutions, nickel is somewhat more noble than copper, and the cupronickels lie somewhere in between. Nickel and its alloys are not readily polarized and, therefore, will cause accelerated corrosion of more active materials such as aluminum and ferrous alloys. Because of the passive films on both alloys, galvanic corrosion between stainless steel and aluminum alloys in seawater is much less severe than would be anticipated by their difference in position on the galvanic series, particularly if the anode/cathode area is favorable. The passive behavior of stainless steels makes them easy to polarize, so that galvanic effects on other metals or alloys tend to be minimized. Iron and steel tend to protect stainless steel in aqueous environments when galvanically coupled. Couples of stainless steel and copper alloys are often used with impunity in freshwater cooling systems. In chloride bearing environments, “galvanically-induced” localized corrosion of some stainless steels occurs in couples with copper or nickel (and their alloys) and other more noble materials. More precise information on the galvanic behavior of stainless steels can be obtained by using polarization curves, critical potentials, and the mixed potential of the galvanic couple.
This dual position in chloride bearing aqueous environments has been the cause of some serious design errors. In the common galvanic series, a noble position is assumed by stainless steels when in the passive state, while they assume a less noble position in the active state. Galvanic attack of stainless steels is difficult to predict because of the influence of passivity.
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