Intergranular attack and intergranular stress corrosion cracking of Alloy 690 TT in high temperature lead-containing caustic solution

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 10g/L of litharge at 330 degrees 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 degrees C after 720h immersion. When adding 100ppm 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 10g/L litharge and 4% sodium hydroxide solution containing 10?g/L litharge at 330 degrees C for 720h 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.