The corrosive sulfur phenomenon can only be countered effectively through Chedcos selective depolarisation; however, Sea Marconi is also able to carry out passivation treatment (erroneously considered by some as a countermeasure to the problem of corrosive sulfur).
This operation consists of adding a passivating additive (ToluilTriazolAmmina or Ciba-Irgamet 39 or NyPass) to the corrosive oil present in the transformer with the aim of protecting copper surfaces from attack by corrosive compounds such as DBDS.

It should be borne in mind, however, that the protective action of passivating

• has an uneven effect,
• which is limited in time
• and has no effect on the action of copper sulfide

as documented cases of failure have already shown:

CIGRE No. 378/2 – 2009

4.1.1 Experiences (C).However, the addition of metal passivators is not a guarantee against failures.For instance, in Brazil, more than 200 shunt reactor oils in service were passivated (in most cases between ½ and 2 years after going into service).It has been reported that 9 of these units failed between one and 24 months after passivation.One explanation for these failures, which led to very corrosive oils and high thermal loads, is that deposition took place very quickly (in the first months after start-up), following which passivation was ineffective.(C).

Finally, it is necessary to clarify that the passivator does not eliminate the cause of the corrosive sulfur problem, i.e. DBDS (and other corrosive sulfur compounds).

[ALT img:Oil additivation with metal passivators]