34
C. ER Element Performance
The basic ER measurement gives percentage of metal thickness loss and is a function of the original
element thickness. Essentially, total metal loss and corrosion rate are given by the following functions:
........................................................ (7)
............................................ (8)
M
L
=
METAL LOSS IN MILS
X
=
INSTRUMENT READING AT ANY GIVEN TIME
X
2
=
INSTRUMENT READING AT TIME t
2
X
1
=
INSTRUMENT READING AT TIME t
1
t
=
TIME LAPSE (DAYS) BETWEEN READINGS X
1
AND X
2
C
R
=
CORROSION RATE IN MILS PER YEAR
K
=
PROBE CONSTANT
The probe constant K is a function of the element thickness and geometry. Table 3 lists the K factors
for various common elements.
M
L
=
X x K
1000
(X
2
- X
1
) x K x 365
1000 t
C
R
=
