Carbon steels are widely used in the oil and gas exploration and production service. However these materials are prone to corrosion and cracking in CO2/H2S. The propensity to cracking increases when higher strength grades are employed. The use of corrosion resistant alloys incurs costs; however these costs are justified in environments where severe corrosion or cracking of cheaper carbon steel is anticipated. Cost reduction can be attained if these materials are coated by an industrial method such as weld cladding onto carbon steel. To understand the behaviour of UNS N06625 weld clad on carbon steel several weld clad specimens were prepared and tested in de-aerated 3.5 wt.% NaCl solution for 30 days in 9.5 MPa CO2 containing 0.5MPa H2S at 120°C. Specimens were also tested in stressed conditions. Microstructural characterization revealed that the ‘swirls’ of carbon steel in the clad specimens were susceptible to sulphide scale formation in the test environment. These swirls can extend up a few hundred micrometres from the fusion line. The stressed specimens showed no visible cracks at 10X magnification.Thus when selecting the thickness of weld cladding on carbon steel one should choose the thickness to avoid swirls reaching the surface of the cladding.

Post-tensioning (PT) has evolved to become an important technology for affecting integrity of large reinforced concrete structures including bridges. In the case of bridges however tendon failures resulting from wire and strand corrosion have been reported as soon as two years post construction. In response to this a series of recent publications introduced and evaluated an analytical modeling approach that projects timing of such failures given statistics that characterize wire corrosion rate (CJ 72(8) 2016 p. 991; CJ 74(2) 2018 p. 241; and CORROSION/18 paper no. 10496). The present study builds upon this model by considering and incorporating first failures arising not only from corrosion related cross section loss but also tensile overload of remaining wires strands and tendons which may or may not have experienced some corrosion and second the number of strands per tendon given that this parameter may vary from one structure to the next and perhaps within a particular structure. The significance of each of these factors is discussed and results are related to the timing of tendon failures on bridge structures.

In oil and gas production and transportation dissimilar materials are frequently combined for technical and economic reasons. However the combination of dissimilar metals can result in corrosion due to galvanic or bimetallic effects. The driving force for this kind of corrosion is the difference of the corrosion potentials of the individual materials in the given environment which causes element currents the magnitude of which depends on the sum of all system resistances (Ohmic Law). Any assessment of the corrosion rates at bimetallic couplings needs the information on the corrosion (rest) potentials of the bimetallic partners in the relevant medium.Due to the lack of consistent literature data a practical galvanic series was established in this work for standard oil country tubular goods (OCTG) steels corrosion resistant alloys (CRA) as well as graphite (as gasket material) in a model sweet upstream environment. From polarization resistance measurements information was obtained on the corrosion rate of the C-steels in the absence of bimetallic coupling. Furthermore the corrosion rates encountered at the partners of bimetallic couples were quantified via mass loss measurements. The results of this work allow better assessment of the severity of bimetallic corrosion and hence a more appropriate selection of materials which prevents corrosion failures increases the integrity of assets and saves costs.