In the introduction to technical standard IEC 62697-1 “Test methods for quantitative determination of corrosive sulfur compounds in unused and used insulating liquids” 2012 (p. 7) states that:
 Sulfur may be present in insulating liquids (used in transformers and other electrical equipment) in various forms
 The total sulfur concentration depends on the origin of the liquid, the refining process, the formulation and the presence of additives
 Additives include antioxidants containing sulfur, such as the DBDS
 Some sulfur compounds are non-corrosive and others are highly corrosive to metal surfaces inside transformers, for example
 The presence of these types of corrosive sulfur has been the direct cause of breakdowns in equipment used for the generation, transmission and distribution of energy for several decades
 The IEC standard has therefore ruled that both new insulating oils and oils already in use must be free of these corrosive sulfur compounds
 The impact of corrosive sulfur is mainly related to the presence of a specific corrosive compound of sulfur: DBDS

Discovery of DBDS

DBDS was identified as the main cause of sulfur corrosion in July 2005 at the Sea Marconi laboratories. The discovery was made whilst analysing oils used in shunt reactors in Brazil, which had suffered catastrophic failures a few days earlier. Sea Marconi, in conjunction with Terna and the University of Missouri, confirmed the discovery after extending the analysis to include other European and South American oils. It was first published on 20 June 2006 in Turin, at the IEC WG 35 meeting on corrosive sulfur. Subsequent publications contained both the methods for detecting DBDS and countermeasures taken by Sea Marconi in Europe and South America to tackle the problem of “DBDS corrosive sulfur – C1” using a process of depolarisation.

Along with the discovery of DBDS as the principle cause of the corrosive sulfur phenomenon (July 2005), Sea Marconi also studied the corrosive action of both the sulfur compounds that are normally found in oil, and degradation by product additives.

How we made the discovery

Thanks to Sea Marconi’s professional expertise, DBDS was discovered during an intervention that we carried out ten years ago for a transformer construction company in South America; the investigation was requested following a series of catastrophic failures of shunt reactors in their first 18-24 months of operation. Studies failed to establish the cause of the catastrophes with any degree of certainty, but served to increase our understanding of various phenomena (eg the part that refining processes play and the tendency of certain oils to dissolve metals), which subsequently led to better understanding of the role that DBDS plays and the reasons why it is used in oils.

The graph shows a significant increase in hydrogen in oil since 1990
The graph shows a significant increase in copper dissolved in oil since 1990
The graph shows a significant reduction in total sulfur in oil since 1990

Click here to see Sea Marconi's major publications on the topic:

V. Tumiatti ? ?CODET ? Sistema di detenzione e smaltimento controllato di trasformatori e condensatori elettrici in Askarel-PCB" - Bollettino Tecnico - Sea Marconi Technologies - Torino 1/10/1979
I. Barbiero, M. Scalabrino, V. Tumiatti ? ?La detenzione controllata e lo smaltimento dei PCB negli impianti industriali e di servizi. Problemi, Sistemi, Soluzioni? Atti del simposio su rischi e tossicita' dell'inquinamento da policlorobifenile-PCB - Milano 12/03/1980.
V. Tumiatti, V. Petrillo - "Sistema tecnologico integrato di detenzione e smaltimento controllato di residui tossici contenenti PCB" ? Atti del convegno internazionale su rifiuti solidi, fanghi e materiali residui ? Roma 17-20/06/1981.
M. Negre, V. Tumiatti - "Prevenzione dei rischi e gestione emergenze su sistemi contenenti PCB. Processi di distruzione termica e chimica di composti tossici clorurati-PCB, PCDD, PCDF "Atti del convegno su solventi e composti organo-clorurati. monitoraggio ambientale e biologico - Padova - maggio 1983.
S. Facchetti - "I Relazione sulle prove preliminari di demolizione chimica di 2,3,7,8 -TCDD (diossina) per decontaminare materiale inquinato con CDP PROCESS- Sea Marconi" - CEE - CCR Euratom of Ispra, maggio 1983.
S. Facchetti - "II Relazione sulle prove preliminari di demolizione chimica di 2,3,7,8 - TCDD (DIOSSINA) per decontaminare materiale inquinato con CDP PROCESS - Sea Marconi " - CEE - CCR Euratom of Ispra, Agosto 1983.
S. Facchetti - "III Relazione. Prove di decontaminazione della 2,3,7,8 - TCDD (diossina) nello stabilimento ICMESA (Reparto TCF): decontaminazione per distruzione chimica eseguite all'interno del Reparto B il 1-6 luglio 1983 con CDP PROCESS - Sea Marconi " "Esperienza di demolizione su campione di 2 mg di 2.3.7.8 - TCDD prova con reattivo Sea Marconi per la ricerca dei prodotti di degradazione ed esame Tossicologico della miscela di reazione" CEE - CCR Euratom of Ispra, Settembre 1983.
H. POIGER - "Toxicity of reaction products generated Upon heating of TCDD with a decontamination - reagent of Sea Marconi" Federal Institute of Technology-Institute of Toxicology - Schwerzenbach ? Switzerland of September 1983.
G. Nobile, V. Tumiatti - "Chemical demolition of 2.3.7.8 TCDD, PCB's and polyalogenated compounds. CDP PROCESS" PCB SEMINAR, Scheveningen, Netherland 28-30/09/1983.
V. Tumiatti; G. Nobile & Altri - "Decomposizione e distruzione chimica di tossici e supertossici alogenati" - CNR progetto finalizzato chimica fine e secondaria ? Sirmione Settembre 1983.
V. Tumiatti ? ?Plant decontamination process strategic materials recovery and chemical destruction of toxic and supertoxic polyalogenated compounds PCB's, PCDD's, PCDF's through CDP PROCESS Sea Marconi? "Decomposizione e distruzione chimica di tossici e supertossici alogenati" OECD - Paris - 10/10/1983.
G. Nobile, V. Tumiatti, - ?Emergency procedures in polychlorobiphenyls contamination. Intervention, Procedures and methods? The IV. informational environment and safety conference. London 27 - 29/03/1984.
V. Tumiatti - "Valutazione dei fattori critici di successo per le operazioni su prodotti pericolosi. Analisi delle fasi di raccolta, trasporto, smaltimento di rifiuti tossici e nocivi. Stato dell'arte in Italia" - Relazione al parlamento europeo - Commissione d'inchiesta sul trattamento delle sostanze tossiche e nocive nella comunità e negli stati membri. Bruxelles - 28/11/1983.
V. Tumiatti, M. Negre & Others - "Integrated system of multidisciplinary tecnical diagnosis and strategic maintenance of energetic, productive and transport plants" - Proceding of the EFMMS Congress European Federation of National Maintenance Societes - Venice 9 - 11/05/1984.
V. Tumiatti - "Caso di emergenza chimica con PCB - diagnosi, decontaminazione e smaltimento". Atti del Congresso Internazionale Emergenza Ambientale 84 - Torino 01/06/1984.
P. Tundo - "Nuovi processi di decontaminazione e distruzione chimica di tossici e supertossici alogenati". Congresso Internazionale Emergenza Ambientale 84 - Torino 01/06/1984.
P. Tundo, V. Tumiatti - "Decomposizione chimica di policlorobifenili e della 2,3,7,8 - Tetraclorodibenzodiossina con CDP PROCESS" ? Ufficio speciale di Seveso - Regione Lombardia - atti del convegno Milano 20-22 Settembre 1984 - La risposta tecnologica agli inquinamenti chimici.
V. Tumiatti - SMT & Others - "Project: decision support software and its experimental validation for menace identification" - EEC - CCR Euratom of Ispra 12/02/1985
P. Tundo, S. Facchetti, V. Tumiatti, U. Fortunati - "Chemical degradation of 2.3.7.8 - TCDD by means of Polyethylenglicols in the presence of weak based and an oxidant" - Chemosphere, Vol. 14, M.5, pp 403-41a - May 1985. Pergamen Press ltd.
G. Nobile - "Degradazione chimica dei composti aromatici policlorurati" - Atti del convegno CNR - giornate della chimica - Sirmione Settembre 1985.
P. Tundo, V. Tumiatti, G. Nobile - "In situ decontamination and chemical degradation of PCDF's and PCDD's coming from pyrolysis of PCB's" ? Proceeding of the American Chemical Society - Conference - New York - 13 -18/04/1986.
P. Tundo - "Decontaminazione Chimica degli alogenuri aromatici tossici" - tecnologie chimiche - Maggio 1986, pp. 96-100.
F. Argentesi, S. Facchetti, V. Tumiatti, S. Cerlesi, et altri - "Ruolo dei sistemi esperti nella gestione della emergenza chimica - "Seminario NBC 1986. Scuola unica interforze per la difesa NBC- ROMA 27 - 28 Novembre 1986.
F. Gardin, V. Tumiatti et altri - "Sistemi esperti: assistenza alle diagnosi di trasformatori elettrici" ? Zerouno - Dicembre 1986.
U.S.E.P.A. - "Liquid reagent destruction of PCB on Surface and concrete" ? R & S ? Permit application of 16/01/1987.
F. Argentesi, S. Facchetti, V. Tumiatti, S. Cerlesi, et altri, - "Progetto di sistemi esperti per la gestione di rifiuti chimici" ?Atti della giornata di studio sui rifiuti urbani e industriali - Milano 16 - 17 Febbraio 1987.
U.S.E.P.A. - "Continuous Treatment of PCB contaminated Hydrocarbons" - R & S Permit application of 16/06/1987.
F. Argentesi, S. Facchetti, V. Tumiatti, S. Cerlesi et Altri - "CHEM: an expert System for the management of chemical accidents involving halogenated aromatic compounds" - Word Conference on Chemical Accident - Rome 7 - 10 July 1987.
P. Tundo, V. Tumiatti, G. Nobile - "Chemical degradation of selected polychlorinated compound by means of polyethers, a base, and an oxidant "American chemical society symposium series 338 - 1987 - Solving hazardous waste problems learhing from dioxins.
V. Tumiatti - "Progetto: valutazione gravità incidente chimico causato dai polialogenati aromatici e contromisure preliminari" - CEE CCR Euratom - Ispra 27/11/1987.
S. Cerlesi, F. Argentesi, V. Tumiatti, G. U. Fortunati. IST. SAN - "Contingency planning: a expert system - CHEM - for describing the level of response needed" - A report of nato/ccms working group on management of accidents involving the release of dioxins and related compounds - Rome 1988.
G. Camino, V. Tumiatti - "Methodes for PCB contamination levels in dielectric liquids" - IEC. International Electrotechnical Commission. Paris 9 - 10/01/1989 - TC 10 Working Group n. 7.
P. Tundo, B. Ruggeri, V. Tumiatti - "A case study on the chemical degradation of polychlorinated compounds by CDP PROCESS: Removal of PCB from oil of an electrical transformer" - V. conferenza internazionale ifiuti solidi, fanghi & materiali residui, Roma 26-29 Aprile 1989.
ENEL - "Risultati del test dimostrativo nella Centrale di Pracomune - CDP PROCESS per la dealogenazione di PCB in olio" - Ente Nazionale per l'energia elettrica - SPT comp. V.ENEZIA. 24/05/1989.
P. Tundo, E. Serena, B. Ruggeri, V. Tumiatti - "A case study on the chemical degradation of polychlorinated compounds by CDP PROCESS; Removal of PCB from oil of the electrical transformer" ? Proceeding of the EPRI-PCB Seminar - San Diego - USA. 03/10/1989.
V. Tumiatti, SMT - "Progetto: "Azioni di censimento dei contenitori ed apparecchi PCB ..." - CEE. CCR Euratom di Ispra 12/12/1989.
G. Sarcina, V. Tumiatti et altri - "Un ipertesto per controllare la diossina" - Zerouno - Gennaio 1990.
B. Ruggeri, P. Tundo, V. Tumiatti - Paper "Supported liquid phase reactor - SLPR - for PCB's in oil decontamination" ? Proceedings of the ISCRE 11 - International Symposium on Chemical Reaction Engineering - Toronto - Canada' 08 - 11/07/1990.
F. Argentesi, S. Facchetti, S. Cerlesi, V. Tumiatti, et Others - Paper "Oil-PCB manager: a risk evaluation and management System for electrical Containers". The International Conference On Organohalogen Compounds - EPRI - PCB Seminar. Bayreuth - FRG. 10 - 14/09/1990.
V. Tumiatti - "Progetto Oil-PCB manager (OPM): sviluppo di un sistema informatico per la gestione di contenitori contaminati da PCB" - CEE - Commissione delle Comunità Europee Istituto dell'Ambiente, Centro Comune di Ricerca. Ispra 13/09/1990.
V. Tumiatti, B. Ruggeri ? ?Lo scenario: il problema PCB nella dinamica socio-economica ed ambientale?, OIL-PCB FORUM?90 ? International Conference ? Turin 6-7 december 1990.
G. Camino, V. Tumiatti ?Prevenzione incidenti: la diagnosi del degrado funzionale nei trasformatori elettrici mediante l?analisi dei prodotti di degradazione chimico-fisica dei componenti interni, OIL-PCB FORUM?90 - International Conference ? Turin 6-7 december 1990.
F. Argentesi, S. Cerlesi, V. Tumiatti ? ?OIL-PCB manager (OPM): un sistema per la gestione di contenitori a rischio?, Oil-PCB Forum ?90 ? International conference-Turin 6-7 december 1990.
S. Carlesi, D. Buga, V. Tumiatti ? ?Analisi statistica dei dati e modellizzazione dell?informazione: priorità azioni di controllo, pianificazione dell?emergenza, previsione fabbisogno smaltimento?, Oil-PCB Forum ?90 Turin 6-7 december 1990.
P. Tundo - ?Il ruolo della chimica nella decontaminazione di sostanze tossiche persistenti?, Oil-PCB Forum ?90 Turin 6-7 december 1990.
V. Tumiatti - "Progetto Q C W: Quality Control of Water" - SMT CEE - Commissione delle Comunità Europee, Istituto dell'Ambiente - Centro Comune di Ricerca Ispra 11/03/1991.
S. Cerlesi, S. Facchetti, C. Orazio, S. Kapila, and V. Tumiatti ? "Modeling techniques for movement of chlorinated organics in terrestrial environment" - Proceedings of the 11th. international symposium on chlorinated dioxins and related compounds - Dioxin 91 - Research Triangle Park - North Carolina. USA September 23-27-1991.
S. Cerlesi, F. Argentesi, G. Camino, S. Facchetti, and Tumiatti ?Diagnostic module for functional degradation as an extention of the OIL-PCB manager (OPM)? - Proceedings of the 1991 PCB Seminar - EPRI - October 8-11-1991 Baltimore USA.
B. Ruggeri, V. Tumiatti, S. Dallo, V. Liu - "PCB's - in-oil decontamination by supported-liquid-phase-reagent (SLPR) used in batch conditions" - Proceedings of the 1991 PCB Seminar - EPRI - October 8-11-1991 ? Baltimore USA.
B. Ruggeri, S. Kapila, G. Camino and V. Tumiatti ? "Determination of relative efficiencies of pcb treatment processes" - Proceedings of the 1991 PCB Seminar EPRI - Baltimore USA - October 8-11-1991.
A. De Pablo, R. Andersson, H.J. Knab, B. Pahlavanpour, M. Randoux, E. Serena, V. Tumiatti ? "Furanic compounds analysis a tool for diagnostic and maintenance of oil-paper insulation systems" - Proceedings of the CIGRE Conference - Berlin Germany - April 22-27-1993.
V. Tumiatti, B. Ruggeri, G. Camino, S. Dallo - ?A new technology for dehalogenation of PCBS and other halogenated contaminants? ? Proceedings of the European meeting on chemical industry and environment ? Girona Spain 2-4 June 1993.
V. Tumiatti, S. Dallo, B. Ruggeri, G. Camino ? "A new technology for dehalogenation of pcbs and other halogenated contaminants" - Proceeding of the 1993 Seminar EPRI - New Orleans, Louisiana USA - September 14-17-1993.
V. Tumiatti, S. Dallo, P. Aglietti and S. Kapila ? ?CDP Process: a new Technology for Continuos dehalogenation of PCBs in oil? ? Proceedings of the 10th International Electric Power Research Institute (EPRI) PCB Seminar, Boston, MA, August 29-31,1995.
K.S. Ryoo, S. Kapila, V. Tumiatti, G. Camino and A.A. Elseewi ? ?CHEDCOS (chemical Decontamination and Counterflow Oxidative System): Application for Desctruction of PCBs? ? Proceedings of the 10th International Electric Power Research Institute (EPRI) PCB Seminar, Boston, MA, August 29-31,1995.
EDF-Etudes et Recherchers ?Le traitement in situ des transformateurs contenant des PCB?, EDF-Electricité de France-Fait marquants 1996.
S. Kapila, V. Tumiatti, G. Boasso, Q. Liù and P. Nam ? ?Plant decontamination through chemical dehalogenation? ? Proceedings of the EA Technology Seminar PCB ? Legislation for Electric Power Network-London 21 october 1997.
V. Tumiatti, G. Di Iorio ? ?Determination of PCBs and PCB related substances (PCTs and PCBTs) CEN/TC19 pr. EN12766-1 Part. 3? ? EU Committee, Bruxelles ? Belgium ? 14 december 1998.
V. Tumiatti, R. Actis, G. Boasso, G. Di Iorio, S. Kapila, A. Porciani ? ?Dehalogenation of PCBs and protection of the environment: application on electrical transformers with a process in Continuous mode? ? (to be presented for SMI?99 ? 3° Convegno internazionale sulla manutenzione di impianti industriali, Bologna 17-20 febbraio 1999).
G. Boasso, A. Decoster, V. Tumiatti, P. Voorspoels ? ?Decontamination of PCBs and protection of the environment: application on electrical transformers with a process in continuous mode in the Republic of Cyprus? ? (to be presented for 1° International Conference on solid waste; Rome 7-9 april 1999).
P. Nam, Q. Liu, S. Kapila, W. Tumiatti and A. Porciani, - "An assessment of radiolysis and chemical dehalogenation for decontamination of PCBs and PCDDs in soil." Organohalogen Compounds, 40, 507-511,1999.
W. Tumiatti, A. Porciani, R. Actis, S. Kapila and P. Nam, - "A Continuous technology for decontamination of PCBs/PCTs/PCDFs/PCDDs in insulating oil - CPD process applications" Organohalogen Compounds, 40, 571-576, 1999.
P. Nam, S. Kapila, Q. Liu, W. Tumiatti, A. Porciani, and V. Flanigan, - ?Solvent Extraction and Tandem Dechlorination for Decontamination of Soil.? Chemosphere, 43, 485-491, (2001).
P. Nam, Q. Liu, S. Kapila, W. Tumiatti, and A. Porciani, - ?An Assessment of Radiolysis and Chemical Dehalogenation for Decontamination of PCBs and PCDDs in Soil? Presented at the Dioxins 99, September 12 ? 17,1999, Venice, Italy
W. Tumiatti, A. Porciani, R. Actis,  S. Kapila and P. Nam, ?A Continuous Technology for Decontamination of Electrical Equipment Through Dechlorination of PCBs/PCTs in Insulating Oil CDP Process®? - Applications Presented at the Dioxins 99, September 12 ? 17,1999, Venice, Italy
A. De Pablo, R. Actis, R. Maina, W. Tumiatti, 88-95 descontaminación de transformadores de aceite contaminados por policlorobifenilos (PCB) /Energía: Revista de Ingeniería Energética, 2003 JUL-AGO (172) Mar 2004
V. Tumiatti, M. Tumiatti, C. Roggero, R. Maina, R. Actis, G. Cravotto, F.   Trotta, Università di Torino ?POPS/ PCBS decontamination of oils, soils and water in electrical  installations? XV.I Congresso nazionale di chimica industriale Verbania Pollanza 14-17 giugno 2005
G. Cravotto, S. Di Carlo, B. Ondruschka, V. Tumiatti, C.M. Roggero ?Decontamination of soil containing POPs by the combined action of solid Fenton-like reagents and microwaves?. Chemosphere. 2007 Oct
A. I. Balabanovich, A. Hornung, M.P. Luda, W. Koch, V. Tumiatti ? ?Pyrolysis study of halogen-containing aromatics reflecting reactions with polypropylene in a post treatment decontamination process.?, Environmental science & technology, 39 (14), p.5469-5474, Jul 2005
G. Cravotto, S. Di Carlo, V. Tumiatti, C. Roggero, D. Bremner ?Degradation of Persistent Organic Pollutants by Fenton?s Reagent Facilitated by Microwave or High-Intensity Ultrasound. Environ. Technol./ *2005*, 26 (4), 721-724.
M. Pompili, V. Tumiatti ?The new CENELEC Standard CLC50503 on PCBs: PCBs Inventory? ? PCBs Elimination Network Magazine, n. 1 November 2010, pagg. 98-99