prEN ISO 21857

This document establishes the general principles to be adopted to minimize the effects of stray current corrosion caused by direct-current (d.c.) on buried or immersed pipeline systems. A brief description of alternating current (a.c.) effects is provided. The document is intended to offer guidance for: — the design of cathodic protection systems which may produce stray currents; — the design of pipeline systems, or elements of pipeline systems, which are to be buried or immersed and which may be subject to stray current corrosion; — the selection of appropriate protection or mitigation measures. The effects of a.c. induced voltages are not dealt with in detail in this document because they are covered in ISO 18086. General principles and guidelines are, however, provided. Stray current corrosion can also occur internally in systems containing a conducting electrolyte e.g. near insulating joints or high resistance pipe joints in pipelines transporting conductive fluids. Internal corrosion risks from stray currents are not dealt with in detail in this document but principles and measures described here can be applicable for minimizing the interference effects. Stray currents can also cause other effects such as overheating. These other effects are not covered in this document. A.C. currents can induce unacceptable touch voltages on above-ground appurtenances of pipeline systems. These are not covered in detail in this document. They are covered in EN 50443, EN 61140, IEC 60364-4-41, IEC TS 60479-1, IEC 60364-5-52, IEC /TS 61201, and IEC TR 60479-5. Systems which may be affected by stray currents include buried or immersed metal structures such as: a) pipeline systems; b) metal sheathed cables; c) tanks and vessels; d) earthing systems; e) steel reinforcement in concrete; f) sheet steel piling. This document provides details only for pipeline systems although the principles can be applied to other buried structures. The EN 50162 series of standards also provide guidance for railway related structures.