High Temperature Corrosion
Behaviour of SS Alloys in Solar Salt
for CSP Plants
Corrosion data analysis of SS-316 and SS-321 to determine which
demonstrates better corrosion resistance for application in CSP plants
What is a CSP plant?
• Collects sunlight with heliostats on a tower in the form of heat energy
• The heat is then used to run a Rankine thermodynamic cycle
What is a CSP plant?
• Main advantage over Photovoltaic solar plants is that the power
output can stay reliably constat despite weather conditions
• That’s because CSP plants have much higher thermal energy storage
• Also CSP plants can easily work in tandum with other types of fuel
• Molten Salts used as HTF, increase efficiency to over 40%
• Typical molten salt is the Solar slat which is 60%NaNO3 + 40%KNO3
Why corrosion is a major factor to consider
• The solar salt has very high consentrations of oxygen
• Along with the high operating temperature and flow conditions the
alloys in the pipes can oxidize faster, CR is imncreased
• This adds to the cost of energy production since the piping will
require replacement
• The lower the pipe replacement rate the lower the cost of production
Experimental methods to measure and
understand the effect of corrosion
• Overall corrosion/weight loss experiments
• Immersion Tests
• Electrochemical Tests
• Morphology Imaging Techniques
• SEM
• Chemical composition of oxide layer
• XRD
Immersion
Electrochemical method
SEM
XRD
Experiment conducted and data gathered
• The SS-316 and SS-321 corrosion behavior was studied for static and
dynamic corrosion
• The alloys where immersed in a molten salt tank on a rotating
aparratus with positions at different radii to simulate different flow
velocities
Data gathered
• Weight loss measurements were taken every 250h up to 1000h
• Corrosion rates are obtained with: 𝑪𝑹 = 𝟖𝟕𝟔𝟎𝟎 ∗ 𝜟𝒎/(𝝆 ∗ 𝑻)
• Cross sectional morphology graphs
• XRD graphs
• SEM pictures
Weight loss data analysis
• SS 316 displays better overall corrosion resistance
• As time passes CR converge to an increasing vallue with respect to
velocity
• With higher velocity this effect happens quicker
• The effect of errosion can be shown from the CR vs Time graphs at
the given velocities
XRD graphs
SS 316
SS 321
Cross sectional morphology SS 316
2 m/s
6 m/s
Cross sectional morphology SS 321
2 m/s
6 m/s
SEM pictures SS 316
2 m/s
4 m/s
6 m/s
SEM pictures SS 321
2 m/s
Intergranular
attack
6 m/s
4 m/s
Pitting
corrosion
Stress corrosion
cracking
Remarks
• SS 316 is better
Conclusion and evaluation