Corrosion Engineering: 4) The critical potential for stress-corossion cracking o
ID: 536311 • Letter: C
Question
Corrosion Engineering:4) The critical potential for stress-corossion cracking of moderately cold-worked 21-6 stainless steel in deaerated NaCl2 solution at 130 degree Celsius is -0.167 V (S.H.E.)
a) What effect on SCC of 21-6 results from coupling to Nickel (corr = -0.21 V)?
b) On adding H2SO4? Why?
c) Under (b), below what value of pH at 130 degree Celsius does the cathode potential 21-6 becomes more noble than critical? Corrosion Engineering:
4) The critical potential for stress-corossion cracking of moderately cold-worked 21-6 stainless steel in deaerated NaCl2 solution at 130 degree Celsius is -0.167 V (S.H.E.)
a) What effect on SCC of 21-6 results from coupling to Nickel (corr = -0.21 V)?
b) On adding H2SO4? Why?
c) Under (b), below what value of pH at 130 degree Celsius does the cathode potential 21-6 becomes more noble than critical? Corrosion Engineering:
4) The critical potential for stress-corossion cracking of moderately cold-worked 21-6 stainless steel in deaerated NaCl2 solution at 130 degree Celsius is -0.167 V (S.H.E.)
a) What effect on SCC of 21-6 results from coupling to Nickel (corr = -0.21 V)?
b) On adding H2SO4? Why?
c) Under (b), below what value of pH at 130 degree Celsius does the cathode potential 21-6 becomes more noble than critical?
Explanation / Answer
Solution:
(a) The coupling of 21-6 SCC and Nickel results in incrased dueo disimilar metal influenced by difference in S.H.E an lead role in corrosion.
(b) by adding sulphuric acid will increase the corrosion rate as the proton from acid results in rapid exchange / acceleration of corrosion rate by potential difference.
(c) under pH = 2 the corrosion is critical (reference from Corrosion Technology textbook appendix)