Test Report
Study of 6NHClCorrosiononCommercial 316SS, HastelloyC-22 andTrueTubeVariants
Figure 3 is the surface of commercial grade 316L tubing
with fused silica coating. Since the coating is transparent
the image shows themetallic surface and not the coating
surface. Because of the irregular surface roughness of the
tubing it is difficult todistinguish anyarea of preferential
attack. Several locationswhere inspectedwith no evidence
of total coating failure.
Figure 3:Commercial Grade SSwithFusedSilica
Coating500x
Figure 4 shows the surface of theElectropolishedTrueTube
EPTubing. Primarycorrosion is evident at the grain
boundarieswith some pitting internal to the grains.
Figure 4:ElectropolishedTrueTube EPTubing500x
Figure 5 is of theTrueTubeEPwith SiltekCoating
(TrueTubeEPS). Themicropitting of themetallic surface
is seen. This is the result of the electropolishing and
coating process not due to corrosion. The basemetal
surface appears untouched by theHCl. Comparing the
samples commercial grade fused silica (Figure 3) explains
the variance in corrosion rate. The discontinuities in the
coating for the fused silica coated commercial grade tubing
aremajor sources ofweight loss and directlyaffect the
corrosion rate.
©2004O’BrienCorporation •QLT-TRTTCORR • 11AUG04
Figure 5:TrueTubeEPS –ElectropolishedTubing
withSiltekCoating500x
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