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Longitudinal welded joints samples of X70 and X80 API grade steel pipes were exposed to a deaerated 1% NaCl solution containing CO2, at temperatures in the range of 25 ºC to 80 ºC for 48 hours. Analogous samples were exposed to the adjacent vapour phase. The layer of corrosion products which formed on the base metal and welded regions of the samples was investigated using mass loss determinations, scanning electron microscopy and X-ray diffraction. The corrosion products formed in tests at 60 ºC and were composed of FeCO3. The FeCO3 which had initially formed at 80 ºC was observed to have subsequently decomposed, resulting in a layer of Fe2O3.

The susceptibility of girth welds to sulphide stress cracking (SSC) and hydrogen embrittlement (HE) were evaluated for API grade X80 and X56 steels, both for similar (X80/X80) and dissimilar (X80/X56) joints. Slow strain rate (SSR) and hydrogen permeation tests were performed at room temperature using sodium thiosulphate solutions at different pH levels. The SSR tests showed that the majority of the welded joints studied, though approved by the API 1104 standard's criteria, did in fact suffer a reduction in ductility and showed indications of susceptibility to sulphide stress cracking and to hydrogen embrittlement in the form of secondary longitudinal and internal transverse cracks. This was true regardless the welding process used.