Corrosion of welded joints is an inevitable issue in oil/gas industry. Welded joints (WJ),which are composed of a base metal (BM), heat affected zone (HAZ) and weld metal (WM),naturally possess compositional and microstructural heterogeneities; therefore, the corrosion behaviour of a welded joint appears erratic and difficult to predict[1]. In this sense, the fundamental research in the electrochemical behaviour of such joint parts is required and will be conducive to guarantee the integrity and safety of the pipeline steel, reducing the risk of corrosion failure of pipeline steel[2]. Weight loss method, classical electrochemical method, wire beam electrode array, micro-electrochemical method and numerical simulation method was implemented to study the localized corrosion behaviour of the X80 steel welded joint in CO2-saturated solutions. The main conclusions are as follows:

Corrosion rates region X80 steel welded joint heat effect on the corrosion rate play a major role. The corrosion rate model between the X80steel welded joint and the isolated regions in the X80 steel welded joint was:

CR=0.107+0.009×CRBM+0.831×CRICHAZ-1.066×CRFGHAZ+0.943×CRCGHAZ+0.158×CRWM. Under the same conditions, the corrosion rate exhibited the following order: ICHAZ > FGHAZ >CGHAZ > WJ > BM > WM. The relationships between the corrosion rate of the X80 steel. welded joint and the solution pH was non-linear.

A new index, namely, the galvanic corrosion intensity factor, was proposed and verified to succeed in characterizing the degree of galvanic corrosion. Based on the finite element method, the prediction model of galvanic corrosion rate of the X80 steel welded joint was established. A new method for the simultaneous determination of electrochemical parameters at different scales over a simulated X80 steel welded joint surface using traditional electrochemical techniques in conjunction with the WBE and SVET methods was developed.

References

[1] Chaves I A, Melchers R E. Corrosion Science, 2011, 53(12): 4026-4032.

[2] Mohammadi F, Eliyan F F, Alfantazi A.Corrosion Science, 2012, 63: 323-333.