# Corrosion Rings-I

```Corrosion rings are sized to fit in the relief groove in the tool joint box in the drill string. Corrosion coupons are
typically used in aging cells in a laboratory environment, or at select locations within the flow line. Both are
exposed to fluid for a period of time and the difference between the initial and the final weights (or the weight
loss) is attributed to corrosion. The corrosion rate is calculated and reported as lb./ft2/yr., or mils per year (my).
The term &quot;mils per year&quot; refers to the loss of metal in thousandths of an inch per year.
Calculations:
lb.ft2/year = Weight loss, grams
Exposure time, hours
xK
Where:
K=
(Weight Loss, grams) (1000)
Sp. gravity x 16.387 x area x year
(coupon)
(ml/in3) (in2) (days/365)
.
Note: The K factor is the constant used for the area of the ring that is exposed and the metal density of
that ring.
mils per year = lb/ft2/year x 24.6
A corrosion rate of 2 lbs/ft2/year or 50 mpy is a reasonable criteria for corrosion rate but this may vary
with individual conditons.