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Case Study Premature Failures of Mild Steel Continuous Slot Well Screens
Technical Memorandum 004-4 - Case Study Premature Failures of Mild Steel Continuous Slot Well Screens Imprimir
Viernes, 15 de Julio de 2011 02:22

 

Executive Summary

Water purveyors in California have experienced premature failures of water wells constructed with mild steel continuous wire-wrapped screen. Laboratory testing was conducted to evaluate the properties of this type of well screen. The results show a clear relationship between the type of steel, the amount of open area in continuous wire-wrapped well screens, and corrosion rates.

Background

Beginning about 1981 well screens constructed of triangular-shaped mild steel wire wrapped around an array of mild steel support rods were introduced and heavily marketed in the southwestern United States. Some water purveyors were attracted to the mild steel wirewrapped screen because of its high percentage of open area and availability in slot sizes smaller than 0.050-inch. However, most selected it as a less expensive alternative to stainless steel continuous wire-wrapped screens.

 

When mild steel continuous wire-wrapped screen was introduced to the water well industry, Roscoe Moss Company (RMC) recognized its clear potential for accelerated corrosion. The most undesirable post-installation scenario was as follows:

1. The mild steel wire and internal rods (with their large surface area) would be subjected to aggressive groundwater quality conditions.

2. The corrosion of the mild steel wire would result in a widening of the numerous slots between the wires.

3. The widened well screen slots would allow aquifer material and gravel pack to pass through the screen and into the well. A portion of the sand would pass through the pump and damage its internal mechanism.

4. The numerous small welds that join the wire to the array of rods would be weakened by corrosion; and, in the worst-case the well screen would collapse.

This memorandum presents a brief overview of laboratory testing that was conducted to assess corrosion effects of mild steel screen. It also includes case studies that briefly describe the experiences of several water purveyors who installed production wells using mild steel continuous wire-wrapped screen.

Laboratory Testing

In 1982 a laboratory testing program was conducted to evaluate the corrosion rates of three types of mild steel well screen: 1) RMC “Standard” louvered screen; 2) RMC “Ful-Flo” louvered screen; and 3) continuous wire-wrapped screen. The testing program began with preparation of mild steel screen samples. Each sample had the following dimensions: 21...

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