SME
Biomaterials · Problem type
Corrosion rate from a weight-loss test
Use this for “A 316L coupon of 10 cm² loses 5 mg in 30 days of saline. Its density is 8 g/cm³. What is its corrosion rate?”
Table
Exposure time (T)
(h)
Corrosion rate (CR)
(mm/yr)
This is an example. Type your own values to start a new problem.
CR (mm/yr)
=
87,600
×
W (g)
A (cm²)
×
T (h)
×
ρ (g/cm³)
Formulas
CR
=
87,600
×
W
A
×
T
×
ρ
0.007604
=
87,600
×
0.005
10 × 720 × 8
Assumptions
•
The metal corrodes evenly over the whole surface, with no pits, so the mass lost is a thin even layer.
•
W is weighed after the corrosion products are cleaned off.
•
CR = 87,600W ÷ (ATρ) takes W in g, A in cm², T in h and ρ in g/cm³.
Step-by-step
WE KNOW
W = 0.005 g, A = 10 cm², T = 720 h, ρ = 8 g/cm³
FIND
corrosion rate (CR)
Step 1 · Find corrosion rate (CR)
Use CR = 87,600 × W ÷ (A × T × ρ)
W
ρA
is
the
thickness
lost
in
cm;
87,600
turns
cm
in
T
hours
into
mm
in
a
year.
CR
=
87,600
×
0.005
10 × 720 × 8
CR
=
87,600
×
0.005
7,200 × 8
CR
=
87,600
×
0.005
57,600
CR
=
438
57,600
CR = 0.007604 mm/yr
Check
Put the numbers back in. Both sides should match.
0.007604
=
87,600
×
0.005
10 × 720 × 8
✓
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