【国外标准】 Standard Guide for External Corrosion Protection of Ductile Iron Pipe Utilizing Polyethylene Encasement Supplemented by Cathodic Protection

4.1 This guide provides basic information on the application of cathodic protection to polyethylene encased ductile iron pipe for engineers, owners, water companies, corrosion consultants, ductile iron (DI) pipe manufacturers and others who have an interest in providing underground corrosion protection to ductile iron pipe.4.2 There are many publications, standards, recommended practices, and specifications for the application of coatings and cathodic protection to steel pipe. However, the metallurgy, chemistry, physical properties, surface composition and texture, coating requirements and electrical continuity of standard production ductile iron pipe are significantly different than those of steel pipe, and coating and cathodic protection specifications written specifically for steel pipe may not be directly applicable to ductile iron pipe. The latest revision of a commonly accepted cathodic protection specification (NACE SP0169) states the following in the forward: “This standard does not include corrosion control methods based on injection of chemicals into the environment, on the use of electrically conductive coatings, or on the use of non-adhered polyethylene encasement (refer to NACE Publication 10A292).” It is the purpose of this guide to summarize publications, case histories, and studies which are available regarding cathodic protection installations of polyethylene encased ductile iron pipe to give the reader guidance on this unique method of protection.4.3 This guide may be utilized with galvanic or impressed current cathodic protection.4.4 This guide is written specifically for ductile iron pipe and does not apply to any other type of piping material. It may also be used for ductile iron fittings, valves, and appurtenances specific to ductile iron piping systems.4.5 This guide references requirements for vendor provided information which should be requested and reviewed by the user.1.1 This guide will discuss standard practices which have been successfully utilized in the field for over 35 years to provide external corrosion protection of polyethylene encased ductile iron pipe supplemented with cathodic protection (CP). This guide may also be used for ductile iron fittings, valves, and other appurtenances specific to ductile iron pipe systems. Case histories and publications reporting on the use of cathodic protection to supplement polyethylene encasement are included as an Appendix in this guide.1.2 Other external corrosion control methods which have been used for ductile iron pipe include, but are not limited to: cathodic protection, metallic zinc coatings, bonded dielectric coatings, dielectric coatings with cathodic protection, and trench improvement. Detailed information on these methods of protection are available from other sources and are beyond the scope of this guide.1.3 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.