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Codina,
Huiles Cosmétiques Naturelles
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Corrosion des inox en présence de chlore
Document intercorr (en
anglais)
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Effet du chlore
sur la corrosion des inox dans de l'eau potable
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| Résiduel de
chlore |
Profondeur maximale
de l'attaque
Localisé et
généralisé
Type 304 et Type 316
|
|
mg/l
|
Moyenne
|
localisée
|
| 304 (µm/an) |
316 (µm/an) |
304 (µm/an) |
316(µm/an) |
| 0 |
0 |
0 |
0 |
0 |
| 0,8-1,0 |
0 |
0 |
0 |
0 |
| 2 |
0 |
0 |
0 |
0 |
| 3 à 5 |
300 |
100 - 400 |
1000-50000 |
300-1000 |
These data indicate that in the 3-5 mg/1-residual
chlorine range, Tape 304L becomes vulnerable to crevice corrosion if the
surface is not maintained clean and free of deposits, heat tint scale,
embedded iron and other injurious defects. Type 316L can be expected to
be more resistant to -corrosion in the 3-5 mg/l range of residual chlorine.
Since residual chlorine may be up to 1.8 mg/l in finished water at the
PWTP in order to meet the 0.2 mg/l minimum at point of use, Type 304L
is a good material for finished water and distribution systems.
Chlorine can also have an indirect effect on stainless steel performance
that is associated with the precipitating of iron and manganese discussed
earlier. In a few inland power plants where there can be substantial amounts
of the gallionella a strain of bacteria, the combination of gallionella-manganese-chlorine
has led to extensive pitting of stainless steel tubing in a few heat exchangers
and condensers. Although this type of corrosion has not been reported
in PWTPs, special precautions would be warranted when substantial quantities
of the rather uncommon gallionella strain of bacteria are known to be
present.
Chlorine, but not ozone, has another important effect. In the moist vapors
just above the water line, chlorine concentrations may reach concentrations
that stain and even pit Type 304 and Type 316 stainless steel. This is
more of a cosmetic problem than structural. One water district has been
using stainless steel structurals in clearwells since the late 1950s and
has not yet encountered the need for replacements. On long exposure, the
staining is followed by shallow general pitting over the whole exposed
surface. Vapor side staining and general pitting attack have been reported
in several PWTPs where pipe galleries were not well ventilated near the
chlorine injection area.
* The system be placed in standby at some
future date.
* Slope horizontal runs sufficiently so they will drain without leaving
a water heel between support points.
*Other guides for the operation and maintenance of stainless steel systems
includes the following practices:
* Establish a schedule to flush out sediment and debris on horizontal
runs of raw water piping.
*During downtime, drain completely and dry or, alternately, circulate
water for one hour daily.
*Dissolve calcium hypochlorite granules before introducing them into or
onto the surface of stainless steel piping for the initial disinfecting.
Calcium hypochlorite granules dissolve slowly and have created a severe
micropitting environment when resting on stainless steel.
*Provide proper ventilation to avoid high chlorine vapor areas.
Mise à jour juillet 2001- Révision 1-
copyright IRH Environnement et Jean-Louis ROUBATY 2001
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