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CHEMICAL TREATMENT
in the weld containing Type 316L metal than the fresh stock solution. This appears to be associated with increased chloride content, proba- bly due to external contamination.
z CP of the tank can inhibit the pitting with application of –1 µA/cm2
of
cathodic current. This current level can keep the potential below the protection potential for pitting, thus preventing the pit nucleation and propagation at the most aggressive conditions.
z The most cost-effective preventive measure to avoid recurrence of the pitting corrosion is to remove the inhibitor from the acid blend.
References );<5 )
¹;\IVLIZL ;XMKQÅKI\QWV
for Carbon Structural Steel" (West Conshohocken, PA: ASTM).
2 C.P. Dillon, Materials Selector for Hazardous Chemicals, Volume 2: Formic, Acetic and Other Organic Acids, Materials Technology Institute Publication MS-2, 1997, p. 64.
3 ASTM A240/A240M-10, "Standard ;XMKQÅKI\QWV NWZ +PZWUQ]U IVL +PZW- mium-Nickel Stainless Steel Plate, Sheet, and Strip for Pressure Vessels and for General Applications" (West Con- shohocken, PA: ASTM).
4 R.C. Newman, Corrosion 57, 12 (2001).
5 H.H. Strehblow, "Mechanisms of Pitting Corrosion," Corrosion Mechanisms in Theory and Practice, Chapt. 7, P. Marcus, J. Oudar, Marcel Dekker, eds., 1st ed., 1995.
6 N.J. Lacycock, R.C. Newman, Corros. Sci. 39, 10-11 (1997): pp. 1,771-1,790.
RAYMUNDO CASE is a staff scientist at ConocoPhillips, Bartlesville Technology Center, Corner of Hwy. 60 and 123, Bartlesville, OK 74004, e-mail: raymundo.case@conocophillips.com. He is a metallurgical engineer with 23 years of experience in materials selection, fitness for service, and corrosion control in the oil and gas industries. He has a Ph.D. from UMIST in the United Kingdom, and is a member of NACE International.
NACE International, Vol. 51, No. 4 April 2012 MATERIALS PERFORMANCE 51
DALE R. MCINTYRE is a principal engineer at ConocoPhillips, e-mail: dale.r.mcintyre@ conocophillips.com. He is a metallurgical engineer with 40 years of experience In materials selection, failure analysis, and corrosion control in the oil and
gas and chemical industries. He has an M.S. degree from the University of Missouri-Rolla and a Ph.D. from the University of Cambridge, United Kingdom. He is a member of NACE.