High temperature and high pressure immersion tests in an autoclave were employed to study the corrosion behaviour of X52 pipeline steel in aqueous solutions containing high concentrations of H 2 S. The corrosion products generated were characterised using scanning electron microscope, energy dispersive spectroscopy and X-ray diffraction. It was seen that at a constant H 2 S concentration of 22 g/l, the corrosion rate increased with increasing temperature up to 90uC, thereafter decreased at 120uC and slightly increased again at 140uC while the corrosion rate increased with H 2 S concentration at a temperature of 90uC. When the temperature and H 2 S concentration increased, the corrosion product converted from iron rich to sulphur rich products in the following sequence: mackinawiteRtroiliteRpyrrhotite, where the microstructure and stability of the corrosion products had an important effect on the corrosion rate. The corrosion film was formed through the combination of the outward diffusion of Fe 2z ions and the inward diffusion of H 2 S and HS 2 species.

Immersion tests were carried out in high temperature lead‐containing caustic solution in a static autoclave. The results showed samples with three surface statuses of Alloy 690 TT suffered from intergranular attack (IGA) after immersion in 10% sodium hydroxide (wt%) with 10 g/L of litharge at 330 °C for different times. With the increasing immersion time, IGA became more severe. Wire cutting samples had the most serious IGA, ground samples followed and electro‐polished samples had the slightest IGA. IGA had developed into IGSCC only in wire cutting samples due to the existence of residual stress. All the specimens at different immersion time tests lost weight. To the same cold‐work samples, with the increasing immersion time, the weight loss increased. No IGA was found in 10% sodium hydroxide solution at 330 °C after 720 h immersion. When adding 100 ppm litharge into 10% sodium hydroxide solution, slight IGA was produced. IGA became more serious and the weight loss of the specimens with three surface statuses increased with the increase of lead concentration. As the results of 1% sodium hydroxide solution containing 10 g/L litharge and 4% sodium hydroxide solution containing 10 g/L litharge at 330 °C for 720 h immersion tests, only slight IGA occurred and the weight of samples with three surface statuses increased. The pH value played an important role in lead‐induced corrosion in caustic solution.

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