Effects of solution environments under disbonded coatings on the corrosion behaviors of X70 pipeline steel in acidic soils

Abstract A rectangle crevice assembly was used to study the effects of cathodic protection (CP) potential, crevice thickness, holiday size, bubbling CO2, and surface condition on the chemical and electrochemical environment of the local solution under disbonded coatings. It is found that the cathodic protection removes dissolved oxygen from the crevice and thus shifts the solution to a more alkaline state. Furthermore, the potential of the steel reaches the protected potential range. The available protection distance increases with the negative applying potential. The steady potential and pH distribution are easily achieved, but the polarization degree is not satisfied within the thinner crevice. The difference in the solution environment is found to correlate to the holiday size. The smaller the holiday, the smaller the difference is. The presence of CO2 inhibits the formation of an alkaline environment. It is also found that the rust layer dramatically decreases the polarization rate in the crevice.

[1]  Wei Ke,et al.  Local environment under simulated disbonded coating on steel pipelines in soil solution , 2008 .

[2]  Xiaogang Li,et al.  Electrochemical corrosion behavior of carbon steel with bulk coating holidays , 2006 .

[3]  N. Sridhar,et al.  Application of a General Reactive Transport Model to Predict Environment Under Disbonded Coatings , 2001 .

[4]  P. G. Fazzini,et al.  Experimental determination of stress corrosion crack rates and service lives in a buried ERW pipeline , 2007 .

[5]  Martin Stratmann,et al.  An electrochemical study of phase-transitions in rust layers , 1983 .

[6]  S. Szabó,et al.  IMPRESSED CURRENT CATHODIC PROTECTION , 2006 .

[7]  D. Chin,et al.  Current Distribution and Electrochemical Environment in a Cathodically Protected Crevice , 1999 .

[8]  J. Perdomo,et al.  Chemical and electrochemical conditions on steel under disbonded coatings: the effect of previously corroded surfaces and wet and dry cycles , 2001 .

[9]  Yufeng Cheng,et al.  Mechanistic investigation of hydrogen-enhanced anodic dissolution of X-70 pipe steel and its implication on near-neutral pH SCC of pipelines , 2007 .

[10]  E. Gamboa,et al.  Fatigue of stress corrosion cracks in X65 pipeline steels , 2008 .

[11]  D. Jones,et al.  Predicting Corrosion and Current Flow within a Disc Crevice on Coated Steels, February 2005 , 2005 .

[12]  D. Chin,et al.  Modeling Transport Process and Current Distribution in a Cathodically Protected Crevice , 2000 .

[13]  M. Puiggali,et al.  Fatigue Crack Initiation on Low-Carbon Steel Pipes in a Near-Neutral-pH Environment under Potential Control Conditions , 2002 .

[14]  J. Perdomo,et al.  Chemical and electrochemical conditions on steel under disbonded coatings: the effect of applied potential, solution resistivity, crevice thickness and holiday size , 2000 .