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A Justification into the Use of Insulation Flanges …

1A Justification into the Use ofInsulation Flanges (and Electrically Discontinuous Hoses) at the Ship/Shore and Ship/Ship InterfaceContents Background Research Electrical Characteristics of Cargo Transfer Hoses Supporting Calculations Inductive Circuits Examples Showing the Effects of Hose Resistance and Inductance Effect of Capacitance Multiple Loading Arms and Parallel Circuits Testing of Insulation Flanges Conclusions and Recommendations References Definitions Appendix 1 Acknowledgements2 Type E insulating gasketNutBolt-studSteelwasherOne-piece insulatingsleeve & washerSteelwasherNutInsulation Flanges have been in wide use for more than three decades and.

4 Although ISGOTT and the IMO publication ‘Recommendations on the Safe Transport of Dangerous Cargoes and Related activities in Port Areas’ (Reference 10), strongly

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Transcription of A Justification into the Use of Insulation Flanges …

1 1A Justification into the Use ofInsulation Flanges (and Electrically Discontinuous Hoses) at the Ship/Shore and Ship/Ship InterfaceContents Background Research Electrical Characteristics of Cargo Transfer Hoses Supporting Calculations Inductive Circuits Examples Showing the Effects of Hose Resistance and Inductance Effect of Capacitance Multiple Loading Arms and Parallel Circuits Testing of Insulation Flanges Conclusions and Recommendations References Definitions Appendix 1 Acknowledgements2 Type E insulating gasketNutBolt-studSteelwasherOne-piece insulatingsleeve & washerSteelwasherNutInsulation Flanges have been in wide use for more than three decades and.

2 While there have been no reported incidents of fires at tanker or gas carrier manifolds that may have been caused by arcing when connecting or disconnecting cargo hoses or arms, their use and effectiveness is still often challenged. This is particularly noticeable by operators with a background of road tanker operations, who are now supplying LNG as bunker purpose of this document is to provide an explanation of how Insulation Flanges provide protection against ignition caused by arcing. Unfortunately, much of the research that was undertaken to prove the benefit of Insulation Flanges has been lost over the last 30 or 40 years, and much of what is left is simply a reference to either isgott (Reference 6) or to the IMO publication Recommendations on the Safe Transport of Dangerous Cargoes and Related Activities in Port Areas (Reference 10), which requires their use.

3 Even a literature search of the IMO archives, which shows support for the use of Insulation Flanges as far back as 1977, does not have any references to the research that was undertaken in their favour. The purpose of this paper is to demonstrate their effectiveness, in support of isgott and the IMO Insulation set3 BackgroundVessels transferring low flash point flammable liquids, at marine terminals or during STS transfer operations, need to take precautions against potential sources of ignition. One possible source is the static charge caused by the passage of certain static accumulator products through the cargo transfer system, which may discharge and cause a high voltage low current spark.

4 Another possible source is the low voltage, high current, galvanic cell that may exist between the ship and shore, which could cause an incendive arc when connecting or disconnecting a conductor , such as a loading arm or electrically continuous hose, to the ship s manifold. Unless suitable precautions are taken, either of these sources have the potential to provide the minimum energy required to ignite hydrocarbon/air mixtures within the flammable range. However, it should be understood that they have different causes and require different against ignitions from static are well documented in numerous publications, including the API document Recommended Practice 2003 Protection Against Ignitions Arising Out of Static, Lightning and Stray Currents (Reference 5), published in 2008, the Shell publication Static Electricity Technical and Safety Aspects (Reference 4), and, of particular relevance to ship/shore operations, Chapter 3 of The International Safety Guide for Oil Tankers and Terminals ( isgott ) (Reference 6).

5 Protection is provided by shore pipelines being bonded together and then earthed onboard the ship, and metallic objects being bonded to the ship s structure, which is then effectively earthed through the seawater, as stated in the Verheil (Reference 2) paper. To protect against the accumulation of static charge, bonding should have a maximum resistance to earth of 1 M , as recommended in the API document Recommended Practice 2003 (Reference 5).Up until the middle of the 1960s it was commonly accepted that protection against low voltage, galvanic circuits could be achieved by the use of a ship/shore bonding wire.

6 Arguably, with many oil product jetties having wooden piles and little electrical power infrastructure, this may have been partly true at this time. For example, Mullett and Johnstone (Reference 8), in their paper published in 1960, advocated the use of a bonding wire between ship and jetty when cathodic protection was potential source of ignition from galvanic circuits is peculiar to the ship/shore interface, particularly when the ship is in salt or brackish water. Although familiar with precautions against static discharge, it is unlikely that operators of road tankers transporting low flashpoint products would have come across this phenomenon until they became involved in bunkering vessels with the 1960s and 70s considerable work was undertaken on this subject, resulting in the conclusion that bonding wires provided no protection against low voltage stray currents and could, in fact, be a source of ignition.

7 This research introduced the concept of Insulation Flanges and demonstrated that they provide an acceptable level of safety. As an illustration of how rapidly research was being undertaken into the effectiveness of Insulation Flanges at this time, the 1st Edition of The International Safety Guide for Oil Tankers & Terminals ( isgott ) (Reference 6), which was published in 1972, recognised bonding between ship and shore, but stated that consideration should be given to the use of insulating Flanges . By the time the 2nd edition was published, in 1984, insulating Flanges were the accepted method of providing protection against low voltage arcing across ship shore transfer systems and attention was drawn to the possible danger of using bonding wires, which is explained in the following isgott and the IMO publication Recommendations on the Safe Transport of Dangerous Cargoes and Related activities in Port Areas (Reference 10), strongly recommended against their use some administrations still require the use of bonding wires.

8 Where this is the case they should be attached to the ship outside of the cargo (or bunkering) area and be isolated by a switch in an Ex enclosure, which should only be closed once the bonding wire has been properly attached to the ship and opened before disconnection of the wire. One of the risks with bonding cables is that in the event of a ship breaking out of its moorings there is a chance that flammable cargo may be released and the bonding cable pulled away from the ship s structure igniting the spill. Furthermore its use may lead people not to worry about the importance of maintenance of the insulating flange, assuming they are is now accepted that protection against these low voltage high current circuits is achieved by the use of an Insulation flange or a single electrically discontinuous hose in each transfer line.

9 These have been in use at the ship shore interface since the 1970s. For example, in 1976 the Tees and Hartlepool Port Authority, in the UK, required their use, as did the Port of London Authority from 1981 when it amended its Petroleum Spirit Bye law . In 1978, the IMO BCH IV sub-committee, the forerunner of today s BLG sub-committee, endorsed the use of Insulation Flanges in document This is also a requirement of its current publication Recommendations on the Safe Transport of Dangerous Cargoes and Related activities in Port Areas (Reference 10).In 1982 the API advised the USCG that a bonding wire was not a satisfactory method of protection and an insulating flange should be installed in the cargo transfer connections.

10 The UK Health & Safety Commission, in its 1987 ACOP Dangerous Substances in Harbour Areas required insulating Flanges to be fitted and also drew attention to the hazards of bonding. As already stated, in 1984 the 2nd edition of isgott required their use and this is still valid for the current (5th), edition as well as its sister publication. The International Safety Guide for Inland Navigation Tank Barges and Terminals: 2010 (ISGINTT) , (Reference 11).These low voltage cells, typically between 200 and 700mV, are mainly generated by galvanic action between the ship and shore that results from different materials in the form of steels, sacrificial anodes and non-ferrous fittings being in a salt or brackish water electrolyte.


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