SCWR Information Meeting April 29-30, 2003

Corrosion Studies at MIT

D.B. Mitton, H. Kim and R.M. Latanision

I-625 tube (210 h, non-deaerated 15 mega ohm water )

I-625 tube (non-deaerated 15 mega ohm water , 210 h, T≈ 419˚C)

OCrNi

Alloy 316 tube (192 h, non-deaerated 15 mega ohm water )

Elemental analysis of the 316 stainless steel tube (192 h, T > 395˚C.)

NiCr Mo OFe

Surface of Alloy 316 (300˚C, 288 h, non-deaerated 15 mega ohm water )

20 µm

Surface of Alloy 625 (300˚C, 288 h, non-deaerated 15 mega ohm water)

Surface of Alloy 625 (300˚C, 288 h, non-deaerated 15 mega ohm water)

Scanning Laser Micrograph and Surface Profile of I-625 (300˚C, 288 h, non-deaerated 15 mega ohm water)

Surface Profile

Pit diameter ≈ 19 µm Pit depth ≈ 4.4 µm

Scanning Laser Micrograph of I-625 Under a Washer (300˚C, 288 h, non-deaerated 15 mega ohm water)

Surface Profile

Pit diameter ≈ 12 µm Pit depth ≈ 2 µm

MoNiCrO

SEM and Elemental Analysis of I-625 (300˚C, 288 h, non-deaerated 15 mega ohm water)

Surface of Alloy 316 (400˚C, 171 h, non-deaerated 15 mega ohm water)

Pitting of Alloy 316 (400˚C, 171 h, non-deaerated 15 mega ohm water)

Surface of Alloy 625 (400˚C, 171 h, 15 Mega Ohm Water)

Pitting of Alloy 625 (400˚C, 171 h, 15 Mega Ohm Water)

Alloy 316-L -Corrosion at the Periphery of a Spacer (500˚C, 96 h, 15 Mega Ohm Water)

2.75 mm

Surface of Alloy 316(500˚C, 240 h, 15 Mega Ohm Water)

Surface of Alloy 625(500˚C, 240 h, 15 Mega Ohm Water)

Instrumented Tube Tests

Heaver oxide formation at locations above the pseudo critical temperature

The oxide formation was significantly heavier for the 316 than for the 625 samples

Increased chromium concentration within the oxide formed above the critical point for alloy 625 – this phenomenon is not observed for the 316 stainless steel tube

Exposure Coupons

Minor pitting of the Alloy-625 samples at 300°C

Pitting of both the 316 stainless steel and the Alloy-625 samples was observed at 400°C

Oxide development for Alloy-625 and 316 samples at 500°C - the oxide formation was significantly heavier for the 316 stainless steel than for the Alloy-625 samples

Serious corrosion was observed at the periphery of a ceramic spacer for 316 stainless steel exposed at 500˚C for 96 hours

Summary