Oxidation Behaviour of Ni‑Base Superalloys in Supercritical Water: A Review

Abstract

| In the quest for creating a sustainable future, coal-fred boil‑
ers and nuclear reactors are increasingly moving towards higher steam
temperatures and pressures that can help in reducing emissions and
increase operational effciencies. This trend has now transitioned to
adopting Advanced Ultra-Supercritical (AUSC) water technology that
involves steam temperatures and pressures as high as 760 ℃ and
32 MPa. This transition poses serious material challenges, and one such
is the demanding steam oxidation resistance expected of the candidate
Ni-base alloys. Steam oxidation is a severe problem that can cause sig‑
nifcant downtime in power generation. Several studies have focused
on testing the steam oxidation resistance of candidate Ni-base alloys in
supercritical water environments under varying test conditions. They dif‑
fer from each other in terms of various operational parameters, includ‑
ing the time, temperature, pressure, alloy surface condition, dissolved
oxygen (DO) content, steam fow/stagnancy conditions, and presence of
additional oxidants like acids, salt, etc. The presence of so many such
variables and the complex interplay between them makes it challeng‑
ing to compare the oxidation performance of various Ni-base alloys and
understand the effect of each operational parameter towards oxidation.
In addition, widely differing opinions are being held about the role of sev‑
eral operating parameters in causing steam oxidation. This review work
is an attempt to consolidate all such relevant works, critically analyze the
results reported, generalize the trends observed, identify the variations
among reported works and throw light on the shortcomings.