Welds pitting corrosion

It is obvious that these physical defects are dangerous in their own right but it is also possible for them to lead to subsequent corrosion problems, e.g. pitting corrosion at superficial non-metallic inclusions and crevice corrosion at pores or cracks. Other weld irregularities which may give rise to crevices include the joint angle, the presence of backing strips and spatter (Fig. 9.29). Butt welds are to be preferred since these produce a crevice-free profile and, furthermore, allow ready removal of corrosive fluxes. 

This method is the simplest of all the methods and is capable of detecting surface flaws such as corrosion, contamination, surface finish and surface discontinuities on joints.47 The discontinuities on joints such as welds, seals, solder connections and adhesive bonds can be detected. General corrosion, qualitative pitting corrosion, stress-corrosion cracking, weld-heat-affected zone attack, erosion corrosion and other type of degradation can be observed by visual examination aided by microscopes with sufficient magnification. Degradation of plastics can also be detected by visual examination. Visual examination is also used in conjunction with other techniques, such as powerful microscopes. 

Resistant to high pitting corrosion. Also available as 316L for welded construction. 

Duplex alloys with a composition around Fe-26Cr-6.5 Ni-3Mo with low carbon and nitrogen have been found to be resistant to chloride SCC, pitting corrosion, and IGC in the as-welded condition (48). 

The RC was sealed with a steel plate over the upper hatch. The welds were attacked by pitting corrosion and yielded in 60 years, allowing access for RPV corrosion to begin. 

With these factors in mind, disc type coupons were chosen. These were similar to the American Sodety for Testing and Materials (ASTM) test coupons but smaller in diameter (100 and 70 mm) to facilitate transport. Single sheet coupons were used to evaluate pitting corrosion on exposed surfaces, and couples or sandwich type coupons were used to simulate crevice and/or galvanic corrosion. The coupons were cleaned and numbered, and the alloy type was identified using a laser scriber. The coupons were stacked in a stainless steel rack. This consisted of a steel pipe welded to a stainless steel base plate and threaded at the other end to hold the coupons in place with a stainless steel nut welded to a hook to enable the rack to be suspended with a nylon rope. A... 

Gamer, A., The Effect of Autogenous Welding on Chloride Pitting Corrosion in Austenitic Stainless Steels, Corrosion, Vol. 35, No. 3, 1979, pp. 108-113. 

Poor workmanship and defective materials can increase corrosion. Water turbulence effects can be increased by poor workmanship, such as the failure to ream burrs from cut ends of copper pipe. This increases the turbulence at the joints and results in erosion of the copper. Excessive and corrosive flux used in soldered coppers joints results in pitting corrosion along the flux runs. Incomplete longitudinal welds in electric resistance welded (ERW) steel pipe result in concentration cell corrosion and rapid corrosion. 

In boiling water reactors chromium steels behave similarly to those in pressurised water reactors. 13% chromium steels withstand the effects of steam (700 °C) in continuous operation [75]. Chromium steels with 13-17% C are especially sensitive to intergranular corrosion after being welded. Also, riveted joints were seen to have pitting corrosion up to 1.7 mm in depth as well as crevice corrosion after one year [76]. 

P pitting, S weld seam corrosion, SCC stress corrosion cracking, () slight corrosion, n.a. no corrosive attack detectable... 

Bilmes, P.D., Llorente, C.L., Saire Huaman, L., Gassa, L.M., Gervasi, C.A. (2005) Microstructure and pitting corrosion of 13CrNiMo weld metals. Corrosion Science, Vol. 48, p.p. 3261-3270, ISSN 0010-938X... 

Pitting corrosion is a well-known corrosion problem for stainless steels. It can come along with sensitivation, i.e. a local Cr depletion can sup>port pitting corrosion. Therefore, any segregation, welding joint, heat treatment etc. can have an impact on pitting corrosion. 

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