Depolarisation against corrosive sulphur in oil

Friday March 17th, 2017

In case of corrosive oils (see issues C1, C2, C3, C4) Sea Marconi implements a service targeted to corrosive sulphur called Chedcos® selective depolarization.

Our solution is effective, economic and lasts because it eliminates the cause of the problem, by removing from the oil both DBDS and other corrosive sulphur compounds (DBDS < 10 mg/Kg). At the same time,depolarization by Sea Marconi restores the oil’s functional properties in accordance with IEC 60422 Ed.4-2012, CIGRE 378-2009 Art. 4.2.

Power transformers treated in 2017: 500
Mass of oil decontaminated against corrosive sulphur in 2017: 7,736 ton

Chedcos® selective depolarisation uses:

  • treatment systems created by Sea Marconi called DMU (Decontamination Modular Unit),
  • patented reagents (S/CHED®) without which the treatments would not be as effective
  • an unparalleled operational method because it is carried out on-site and in a closed circuit, meaning that the transformer is not emptied, not even partially
  • appropriate safety procedures also for the “On-Load” mode, mean that the transformer can be kept in service and filled for the duration of the treatment.
  • highly qualified staff

Do you need more information? Do you need a quotation?

The Sea Marconi's depolarization against corrosive sulphur is among the countermeasures indicated in regulations

Extract "corrosive sulfur" from tab. 5 of IEC 60422 ed. 4-2013

Operating modes

Sea Marconi’s extraordinary results are based upon its experience in the industry since 1968, the use of Decontamination Modular Units (DMU), designed and manufactured internally, and the formulation of specific reactants (S/CHED®, etc.) used depending on the operating scenario.

The DMUs are connected to the transformer via flexible hoses, after which the decontamination process is started: the insulating fluid circulates through the DMUs where it is:heated, degassed, dehumidified, and filtered and depolarised (through special patented reactants) to then returned to the transformer, which is never emptied, not even partially.

The continuous circulation of the insulating liquid creates a constant flow of fluid in the transformer that favors the elimination of deposits (sludge) on papers and in the case.

The process can be done safely thanks to

  • low process temperatures,
  • the use of patented reactants that are not explosive or flammable,
  • the use of special piping (SpillGuard®) which can stop the process if there are any accidential leaks but also thanks to
  • a software control system able to check in real time that the process is taking place safely as well as guaranteeing quality, 24 hours a day even without the supervision of an operator.

The treatment is performed with the On-Load option, keeping the transformer in service, under tension and filled, i.e. without any loss of production (with international experience also in nuclear power stations and transformers up to 760 MVA and 500 KV).

The service includes the following activities:

  • Transport before/after of specialized technicians, treatment units (DMU), equipment, reactants and disposable objects from the Sea Marconi office to the sites of the transformers;
  • The Hydraulic and electrical installation and set up of the mobile depolarisation units (DMU)
  • Sampling, analysis and diagnosis (Deosvision®) before treatment (if any);
  • Depolarization treatment against acidity (Chedcos®);
  • Treatment quality control with on site measurement kit SM-TAN;
  • Physical decontamination treatment (degassing and dehydration in a vacuum);
  • Monitoring the treatment parameters;
  • An oil change for transformers in service (if necessary);
  • Level and vent controls;
  • Replacement of desiccant salts in silica gel;
  • Sampling, analysis and diagnosis (Deosvision®) at the end of the process;
  • Oil inhibition with antioxidant additive DBPC (if necessary), should the initial conditions of the oil be such as to arouse suspicion that the oil has lost resistance to oxidation


Removal of corrosive sulphur compounds (DBDS and others)
Removal of inorganic polar compounds (metals)
Removal of soluble and insoluble oxidation compounds (acids)
Removal of water and physical contaminants from oil
Restoration of the oil’s dielectric properties

and of course all the benefits that come with using Sea Marconi treatments:

  • Operational safety is due to using solid patented reactants, low process temperature (80-100 ° C), the lack of emptying the transformer, the use of a decontamination modular unit (DMU) created by Sea Marconi and equipped with an advanced monitoring system, providing 24 hour a day automatic safety
  • Environmental safety because Chedcos® avoids both the replacement, disposal, transfer and handling of enormous amounts of oil that can still be used, and the risks associated with handling contaminated oil
  • The treatment units’ small dimensions mean they are operational even under extreme logistical constraints (e.g . in bunkers, and mines)
  • Functional recovery of oil and transformers through the unique closed-loop operating mode
  • Reference and regulatory compliance IEC 60422 Ed. 4 2013
  • Strong case studies

The Chedcos® treatment makes it possible to avoid the logistical and operational issues of an oil change. The new oil would still be contaminated by DBDS (or other corrosive sulphur compounds) present in the “old” oil that would remain in the papers and which would be released shortly after the oil change. Not only changing the oil involves turning off the transformer but also functional risks (eg.: electrical discharges) for air bubbles and atmospheric moisture.


DBDS < 10 mg/Kg
Total corrosive sulfur (TCS) < 10 mg/Kg (as DBDSeq)

Supplementary worksheet


Sea Marconi Treatments vs Oil replacement  (354.1 KiB)


Sea Marconi Treatments vs Fuller earth  (379.5 KiB)

You did not find what you were looking for?

Contact us to learn more about your case

    I read the privacy information and authorize the use of my personal data for the purposes specified therein.
    Insert this code: captcha