Insulated coupling

Recently in some types of refuelling stations, corrosion-resistant materials have been used between the filter-water separator and the outlet pipeline and valves, usually stainless steel, rarely aluminum. If these are buried, they must have good insulating coating and be electrically separated from other tank installations by insulating couplings. 

Cathodic protection of different materials in installations of dissimilar metals is only possible if the protection potential ranges of the individual materials overlap. Section 2.4 gives information on the protection potential ranges of various systems. If there is no overlapping, then insulating couplings must be installed. This is also appropriate and even necessary if the protection current densities are very different. 

If the individual materials are separated by insulating couplings but connected to a protection system, the connections must be made through diodes to avoid bimetallic corrosion when the protection system is shut down (see Fig. 11-6). Furthermore, the different protection currents should be adjusted via variable resistors. 

Mutskov V), Farrell CM, Wade PA, Wolffe AP, Felsenfeld G. 2002. The barrier function of an insulator couples high histone acetylation lev-... 

It may be desirable to electrically isolate a cathodically protected structure from all other metallic structures, such as connecting lines, pump stations, terminals, etc. If the installation is not isolated, these connections also will be cathodically protected, and current requirements frequently will be excessive. Electrical insulation of pipelines and other structures is accomplished by dielectric isolation. Small lines may be insulated by insulating couplings or unions. If feasible, insulated flanges should be assembled and electrically tested with an ohmmeter before being connected into a line. 

Steel reinforcements in concrete, being passive, are noble in potential with respect to steel outside the concrete that is galvanically coupled to the reinforcements. The measured potential difference is in the order of 0.5 V [62]. The effect of large cathode area and small anode area has caused premature failures of buried steel pipe entering a concrete building [63]. In this situation, use of epoxy-coated reinforcements (to coat the cathode) or insulated couplings should prove beneficial. 

Figure 12.3. Effect of current flowing along a buried pipeline on corrosion near insulated couplings.

Fig. 10-3 Section through an insulated coupling for direct burial.

With AI, An and B-classified installations on electrified railways, spark gaps in the danger zone must be explosion proof [12]. Insulating couplings and spark... 

It is a flangeless factory assembled pipe-length which incorporates an insulating coupling. 

Insulating couplings should be used to separate metallic slrucmres for control of stray current corrosion (see Figure 9.27). 

Where possible the continuity of the leakage current path back to the substation should be interrupted by introduction of insulating couplings in the critical structure. Where continuity of plant, for protection or interference reasons is necessary, the insulating couplings can be bridged with resistors or capacitors. Cathodic protection should be used, preferably with automatic control. 

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