Stress corrosion cracking of alloys 690, 800, and 600 in acid environments containing copper oxides

Book · Tue Oct 01 04:00:00 EDT 1996

OSTI ID:367721

Pierson, E; Stubbe, J; Deny, G ^[1]

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1. Laborelec, Linkebeek (Belgium)

Secondary side stress corrosion cracking (SCC) of steam generator (SG) tubes may be due to the formation of an acid environment in crevices, as demonstrated for several Belgian PWR plants. The susceptibility of alloys 600 and 800 in this type of environment, which had been partially evidenced by several laboratory works, has been confirmed by capsule tests performed at Laborelec, whereas the SCC resistance of alloy 690 always appeared excellent. Capsule tests have been recently conducted at 320 C with the same heats of tubings in the same acid solutions (cationic resins + magnetite + sodium silicate, with or without lead, and sodium sulfate + iron sulfate, with or without lead oxide) containing CuO and Cu{sub 2}O. It appeared that the SCC resistance of the three alloys was generally reduced by the addition of copper oxides, at least when the cover gas did not contain hydrogen. The situation was particularly dramatic for the capsules made of alloy 690 tubing: most of them developed deep cracks, sometimes throughwall (the shortest time to failure being less than 50 h) whereas the same solutions without copper oxides had produced no cracking at all in alloy 690 capsules exposed during more than 2,000 h. Although the corrosion is reduced in presence of hydrazine or at lower concentration, copper oxides probably contribute significantly to the degradation of the tubes in alloy 600, at least in SG`s forming acid sulfate crevice environments. This is also an issue for the new SG`s, especially for those equipped with tubes in alloy 690 TT, particularly for the top of the tubesheet which is a critical deposit area since the high stresses and strains resulting from the expansion of the tube in the tubesheet lead to a risk of circumferential cracking at the transition.

• OSTI ID: 367721
• Report Number(s): CONF-960389--
• Country of Publication: United States
• Language: English

Related Subjects

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS
36 MATERIALS SCIENCE
ACID SULFATES
COPPER OXIDES
CORROSIVE EFFECTS
CRACK PROPAGATION
DOEL-4 REACTOR
EXPERIMENTAL DATA
INCOLOY 800
INCONEL 600
INCONEL 690
SECONDARY COOLANT CIRCUITS
STEAM GENERATORS
STRESS CORROSION
TUBES