Test Report
Study of 6NHClCorrosiononCommercial 316SS, HastelloyC-22 andTrueTubeVariants
DeterminationofTestData
The corrosion ratewas determined using theASTM equation established inASTMG31.
)
(
)
(
TDA
WK ate
CorrosionR
⋅ ⋅
⋅
=
Where:
K is a constant =3.45E6
W is theweight loss in grams
A is the exposed surfaceArea cm2
D is the densityg/cm2
T is the time in hours
The variance of each sample populationwas computed todetermine a confidence level for the results. The variance
was less than 1 for all samples except fused silica coating on commercial tubing. Variancewas calculated by the
equation:
n
x x
∑
−
)
(
where x is the samplemean and n the sample size.
Micrographic InspectionofTest Samples
In addition to the corrosion testingmicrographs of the sampleswhere taken at 500x after the exposure to6NHCl.
All themicrographs taken are of the surface after exposure to6NHCl.
Figure 1 is themicrograph ofHastelloyC-22. It clearly
shows that the 6MHCl has barely touched the surface.
Figure 1:HastelloyC-22 500x
©2004O’BrienCorporation •QLT-TRTTCORR • 11AUG04
Figure 2 shows the surface of the commercial 316LSS
sample. There are several corrosionmechanisms occurring
here. The darken lines indicate grain boundaryattack.
There is alsogeneral corrosion due to the irregular surface
and some pitting. Comparing themicrographs of the
commercial 316LSS tubing and theTrueTubeEP tubing
illustrates the importance ofminimizing nucleation sites in
which pitting and general corrosion can occur. In the case
of the commercial tubing the nucleation sites are the peaks
and valley’s on the surface and process contamination. The
electropolishedTrueTubeEP processminimizes these
nucleation sites.
Figure 2:Commercial 316LSSTubing500x
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