Page 376 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

354 CONSEQUENCES OF CORROSION

(a) (b)
Figure 5.36 (a, b) Copper oxide ringlets round pits. (Figure originally published in Refer-
ence 26. Reproduced with permission of the Canadian Institute of Mining, Metallurgy and
Petroleum. www.cim.org.)

Pit propagation can take place because of the redeposition of copper. This reaction
is driven by low pH and high copper ion concentration inside a pit as observed by the
redeposition of copper around a pit.

Conclusions Pit initiation takes place in areas where oxide film is damaged or
broken. Pit propagation could occur without oxygen and is accelerated by the copper
redepositing reaction. Thus in such a case, prevention of pit initiation is important.

5.3.7.4.11 High-Temperature Corrosion and Wear Problems High-temperature
corrosion and wear occurs in: (i) waste incineration, (ii) fossil energy, (iii) pulp and
paper; (iv) petroleum refining; (v) the chemical and petrochemical industries; (vi)
mining and smelting operations.
One of the methods to alleviate corrosion and wear and its control is judicial selec-
tion of an alloy for the plant design and maintenance followed by a weld metal overlay
of the plant equipment to avoid corrosion failures. Some of the industrial applications
of uniform overlay technology are given in Table 5.8.
A failed 310 stainless steel tube in a waste-to-energy boiler is shown in Figure 5.37.
The appearance of uniform composite tubes with alloy 625 overlay on Cr, Mo steel
is shown in Figure 5.38. Figure 5.39 shows the 309 overlay on Cr, Mo boiler tube in
service in a coal-fired boiler free from corrosion and cracking for 7 years (30).

5.3.7.4.12 Equipment Cracking Failure Case Studies Equipment fails either alone
or in combination with other factors, including substandard materials, improper mate-
rial selection, poor design, equipment abuse, unexpected stresses or environmental
conditions, and poor maintenance practices and/or neglect. Many failures, in one way
or another, involve human error to some extent.