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Design Considerations for Selecting Casing for ASR Wells: Use of Epoxy-Coated Steel or High Strength, Low Alloy Steel
Technical Memorandum 004-7 - Design Considerations for Selecting Casing for ASR Wells: Use of Epoxy-Coated Steel or High Strength, Low Alloy Steel Imprimir
Domingo, 24 de Julio de 2011 20:07



Many new aquifer storage and recovery (ASR) wells have been installed in recent years as part of a concerted effort to better manage ground-water resources. The majority of ASR wells have been constructed with stainless steel (casing and screen); the attributes of stainless steel for these applications are well known. As an alternative to stainless steel, some ASR well designers have selected high-strength low alloy steel (HSLA) for its strength, durability, utility, useful life, and cost. Another alternative for casing material is epoxy-coated mild steel pipe, which has been installed in recently constructed ASR wells. This memorandum presents a brief comparison between epoxy-coated steel pipe and HSLA steel for ASR well construction.



Applicable ANSI/AWWA Standard The American National Standards Institute (ANSI)/American Water Works Association (AWWA) Standard C210-03, entitled Liquid-Epoxy Coating Systems for the Interior and Exterior of Steel Water Pipelines is the applicable standard that provides guidance to the water industry in selecting and evaluating liquid-epoxy coatings for use in potable water service. The standard provides options for the epoxy coating and lining systems such as a) a two part primer and topcoat; b) two or more coats of the same two-part coating; or c) a single coat of two-part coating. The minimum thickness of the coating is to be at least 16 mils (406 μm).

The standard also includes guidance on the field procedures for the use of liquid-epoxy coated pipe for pipeline construction. It does not make specific reference to water well construction. However, it does indicate that precautions should be taken to minimize damage to the protective coating. It recommends against the use of metal tools or heavy objects to contact the finished coating. In the event that the coating is damaged, the standard indicates that the pipe should be reprocessed and recoated. In reference to the use of coated pipe for an ASR well, removal of the pipe for reprocessing and recoating is not a viable option. It would have to remain in place.

Use of Epoxy-Coated Pipe for Water Well Casing Epoxy-coated pipe is known for its use in water transmission pipe; however, its use as water well casing is relatively new. Proponents of epoxy-coated pipe refer to its reduction or elimination of the steel surface area that is subject to rusting (Pyne, 1995). The production of rust from steel casing is, of course, undesirable for ASR wells because the particulate matter might clog the aquifer. However, the application of a liner material to mild steel pipe to achieve non-rust producing conditions comes with some considerations. The first is the epoxy itself. It is widely recognized that a coating material can fail if not properly applied. It is also known that it is almost impossible to avoid some pinholes or holidays when applying a Roscoe...