Corrosion in Water Wells

Part 2. Evaluation of materials for water well construction based on corrosion resistance.

By Thom Hanna, PG

In this second part of our series on corrosion and material selection, we will discuss materials and how they react to the water well environment.

Water wells are essential components of groundwater extraction systems serving municipal, agricultural, and industrial purposes. Their long-term performance depends heavily on appropriate material selection during design and construction.

Corrosion represents one of the primary challenges affecting well longevity, leading to mechanical failure, contamination, and costly maintenance (Hanna et al. 2016). Materials used in water wells—such as casings, screens, and pumps—must endure exposure to groundwater chemistry, mechanical stresses, and variable operating conditions while maintaining structural integrity over decades.

Carbon steels have been widely used in water well construction historically because of their availability and low cost. However, their susceptibility to corrosion in aggressive environments significantly limits their service life (Clarke 1980).

Advances in metallurgy and polymer science have introduced a variety of alternatives including high-strength low-alloy (HSLA) steels, stainless steels, and polyvinyl chloride (PVC). Each material provides a unique balance between mechanical properties, corrosion resistance, and cost.

This column evaluates these materials to identify the most corrosion-resistant and cost-effective choices for different hydrogeochemical conditions, with emphasis on well environments encountered in potable water supply and industrial applications. We will focus on metals and their reactions to the environment, which is shown in a simple corrosion cell in Figure 1.

In a water well, a simple galvanic corrosion cell can form on a steel casing even when no second metal is present. Variations along the casing surface—such as differences in oxygen concentration, soil chemistry, water flow, or surface condition—create local anodic and cathodic areas.

The anodic regions of the steel undergo oxidation and corrode, releasing iron ions into the surrounding groundwater, while nearby cathodic areas support reduction reactions, typically involving dissolved oxygen. Groundwater acts as the electrolyte, allowing ionic current to flow and completing the electrochemical circuit. This localized galvanic action can lead to pitting and uneven wall loss along the steel casing over time.

Materials and Their Corrosion Characteristics

Carbon steels, low carbon steel (LCS), and HSLA (high-strength low-alloy) are among the most common materials used in water well casings and screens. They typically contain about 0.26% carbon with small amounts of manganese, silicon, and copper (Table 1) (Van Droffelaar and Atkinson 1995).

While mechanically strong and inexpensive, these steels are highly susceptible to electrochemical corrosion, particularly when exposed to groundwater containing oxygen, chlorides, or carbon dioxide (Clarke 1980). Over time, corrosion can result in thinning, pitting, and eventual perforation of well casings, compromising water quality and structural stability.

HSLA steels are micro-alloyed with trace amounts of nickel, chromium, molybdenum, and other elements intended to increase mechanical strength and atmospheric corrosion resistance. However, multiple studies (Ahrens 1966; Badrak 2012a) have shown that these micro-alloying elements do not provide significant improvement in corrosion resistance in water well environments compared to low carbon steel.

In saturated groundwater, the microstructure of HSLA steels behaves similarly to that of plain carbon steels, forming localized galvanic cells that accelerate corrosion. Therefore, HSLA steels should be considered primarily for applications where mechanical strength—not corrosion resistance—is the primary requirement.

Stainless Steels: 304 and 316 Stainless Steels

Type 304 stainless steel is an austenitic alloy containing approximately 18% chromium and 8% nickel (Zapffe 1949; Edstrom Industries 2022). Its corrosion resistance derives from a thin, continuous, self-healing chromium oxide (Cr2O3) passive film that forms spontaneously in the presence of oxygen.

In potable and moderately aggressive groundwater, this passive film provides orders-of-magnitude reduction in corrosion rate compared to carbon steels. Type 304 performs well in low- to moderate-chloride waters but is susceptible to pitting and crevice corrosion when chloride concentrations exceed approximately 300 mg/L, particularly under stagnant or low-oxygen conditions.

Sometimes you will see stainless steels designated as 304L or 316. This refers to low carbon that helps prevent weld decay, which is typically not important in water well applications.

Type 316 stainless steel builds on the corrosion resistance of Type 304 through the addition of 2% to 3% molybdenum (Zapffe 1949; Hanna et al. 2016). Molybdenum significantly enhances resistance to chloride-induced pitting and crevice corrosion and improves performance in higher-temperature and higher-TDS waters.

Among the materials evaluated, Type 316 offers the best balance of corrosion resistance, mechanical properties, availability, and cost for demanding groundwater environments. When properly designed and fabricated, 316 stainless steel wells routinely achieve service lives exceeding 50 years.

Corrosion Resistance in Potable Water Environments

Stainless steel is highly corrosion-resistant in most potable water environments due to the stability of their passive chromium oxide film. In neutral to slightly alkaline potable waters (pH 7–9), this oxide layer remains continuous and self-healing (Figure 2), preventing oxygen and chlorides from penetrating to the metal substrate (Hanna et al. 2016).

Even when the surface film is scratched or abraded, it reforms rapidly in the presence of dissolved oxygen, maintaining protection without the need for coatings or cathodic systems (Edstrom Industries 2022). Nickel enhances the ductility and toughness of the alloy while stabilizing the austenitic structure, which aids in preventing stress corrosion cracking. The addition of molybdenum, particularly in Type 316 and 316L stainless steels, further increases resistance to localized corrosion, especially pitting caused by trace chloride ions (Zapffe 1949).

Because most potable waters are low in chloride (<300 mg/L) and near neutral in pH, the passive film on stainless steels remains intact for decades, resulting in negligible metal loss or contamination risk. This passive protection mechanism explains the widespread use of stainless steels in municipal wells, food-grade pipelines, and drinking water systems where long-term corrosion resistance and cleanliness are paramount. The passive oxide coating does not set up in carbon steel, be it either LCS or HSLA (Figure 3).

Environmental Factors and Performance Studies

The corrosion resistance of water well materials is strongly governed by hydrochemical and environmental conditions including pH, chloride concentration, total dissolved solids, temperature, flow velocity, and microbiological activity. These factors control electrochemical reactions on metal surfaces and determine whether protective passive films remain stable or break down.

Waters with low pH accelerate corrosion, particularly in carbon and HSLA steels, because acidic conditions dissolve oxide layers and destabilize carbonate films. Neutral to slightly alkaline waters promote passive stability on stainless steels, while fluctuating pH during pumping cycles or degassing can remove protective films just as oxygen becomes more available near the static water level.

Chloride ions are especially aggressive because they disrupt passive films and initiate pitting or crevice attacks. In groundwater environments with chloride concentrations above 300 mg/L, Type 316 or duplex stainless steels are recommended to resist chloride-induced breakdown of passivity (Hanna et al. 2016).

High TDS levels increase electrical conductivity, enhancing electrochemical activity at the metal surface and accelerating corrosion. Higher temperatures increase reaction kinetics and reduce protective film stability, often doubling corrosion rates for every 10°C increase.

Flow velocity further shapes corrosion behavior by controlling how corrosion products, passive films, and biofilms form and detach. Excessive flow mechanically removes protective layers (Figure 4), leading to erosion-corrosion, while stagnant or low-flow conditions promote differential aeration cells that drive localized attack (Badrak 2012a).

These stagnant zones also support biofilm formation and the activity of microorganisms that contribute to microbiologically induced corrosion. MIC interacts strongly with the chemical drivers of corrosion, often accelerating metal loss beyond what pH, temperature, or chloride levels alone would predict.

Iron-related bacteria, sulfate-reducing bacteria, and slime-forming organisms colonize on casings, screens, and pump components, producing biofilms that trap water and create corrosive micro-zones. Beneath these deposits, oxygen becomes depleted or acidic and sulfide byproducts accumulate, promoting deep pitting.

Warm temperatures increase microbial metabolism, while stagnant conditions near the static water level or behind mineral deposits favor colonization. Flow velocity influences MIC because moderate velocity can shear off early biofilms, while sheltered areas such as crevices, threads, pits, and encrusted surfaces allow bacteria to thrive even when overall flow is high.

Laboratory research by Badrak (2012a, 2012b) and others has validated these environmental relationships under controlled conditions. Testing demonstrated that 316 stainless steel maintains passive stability across broad ranges of pH, chloride levels, and temperature, while LCS and HSLA steels corrode rapidly in similar environments.

In static tests, low carbon steel exhibited uniform corrosion, tuberculation, and scaling, whereas 316 stainless steel showed negligible weight loss (Badrak 2012a). Under dynamic flow, stainless steel continued to resist corrosion because their passive films re-formed rapidly after minor mechanical damage
(Badrak 2012b). These findings align with the known behavior of stainless steels in wells, where their chromium-rich passive layers can re-form quickly unless overwhelmed by high chlorides, low pH, or severe MIC activity.

Field evaluations from mining, municipal, and dewatering wells confirmed laboratory trends. Stainless steels—especially 316 and duplex grades—show long-term stability, minimal pitting, and negligible wall loss over multi-year operation in high-chloride, high-TDS, and elevated-temperature waters (Badrak 2012b; Hanna et al. 2016).

Field failures in carbon steel casings are concentrated near the static water level, where oxygen ingress, temperature gradients, pH shifts, mineral deposition, and MIC combine to produce severe pitting and perforation. These patterns reinforce the predictability of corrosion behavior based on local hydrogeochemical and biological conditions.

Wells operating in waters exceeding 500 mg/L TDS, chloride concentrations above 300 mg/L, or temperatures above 40°C should avoid carbon or HSLA steels, as their corrosion rate increases exponentially under these conditions (Hanna et al. 2016). In contrast, 316 stainless steel and duplex alloys maintain protective passive films, resist MIC more effectively, and provide service lives exceeding 50 years when professionally designed and maintained.

The Nail Test—A Practical Indicator of Corrosion Potential

The nail test is a simple, inexpensive field method used to estimate how corrosive well water may be toward steel casings and pump components. It works by using a low carbon steel nail as a stand-in for the steel found in well structures. Because the nail’s metal is softer and more chemically reactive than casing steel, it reacts more quickly to corrosive water, providing an early indication of water aggressiveness.

When placed in a sample of well water, the nail reacts with dissolved oxygen and minerals. If the water is corrosive, a pink or reddish tint will develop within a few hours as the nail begins to oxidize. This reaction mimics the slow corrosion that would occur on steel surfaces inside a well over months or years. The faster the color develops, the more aggressive the water is toward metal.

In a working well, moving water usually carries oxygen away from the casing, reducing direct oxidation. When the well sits idle, however, oxygen remains in contact with metal surfaces and corrosion accelerates. The nail test reproduces this static condition, making it an effective small-scale model for long-term corrosion behavior in an inactive well.

The Langelier Saturation Index helps interpret the results. The LSI predicts whether water will deposit a protective calcium carbonate film or dissolve it.

• A slightly positive LSI (0.2–0.5) suggests the water can form a thin scale that limits corrosion.
• A negative or weakly positive LSI indicates that the water lacks buffering capacity and will likely be corrosive during idle periods.

If the nail corrodes quickly (Figure 5) even when the LSI appears favorable, it signals that other factors like oxygen, biological activity, or degassing are undermining the water’s stability.

Test Procedure

1. Place an uncoated carbon steel, 6-penny common nail in about 200 mL (6-7 ounces) of well or aquifer water.
2. Use a clear glass jar or beaker so changes are easy to see.
3. Leave the container undisturbed for 24 hours at room temperature.

Interpretation:

• Color within 3 hours: Highly corrosive
• Color between 3 to 24 hours: Moderately corrosive
• No color after 24 hours: Non-corrosive or chemically balanced.

A qualitative evaluation of the color can be used as a corrosion indicator. As corrosion starts, iron oxidizes in stages:

1. Iron (Fe²⁺) reacts with oxygen to form ferrous oxide (FeO).
2. Ferrous oxide combines with water to form ferric oxyhydroxide [FeO(OH)], producing a pink or red hue.
3. Over time, this changes into ferric oxide (Fe₂O₃), the familiar brown or black rust deposit.

These changes parallel to what occurs on well casings when oxygen and mineral balance shift toward corrosion.

Interpreting and Using Results

While the nail test does not capture all real-world influences such as bacterial growth, sediment abrasion, or under-deposit corrosion, it provides a clear first indication of whether the water’s chemistry is protective or aggressive. Rapid color development points to corrosive tendencies that can worsen with biological activity or stagnant conditions. A clean nail after 24 hours indicates stable chemistry and adequate buffering capacity.

In essence, the nail test serves as a small-scale predictor of well health. It links laboratory chemistry, such as pH and LSI, to practical field observation and offers an early warning of potential corrosion problems before they appear in the well itself.

Material Selection Guidelines

The selection of materials for water well construction should balance corrosion resistance, mechanical strength, and economic feasibility (Figure 6). Based on the compiled data (Badrak 2012a; Hanna et al. 2016), the following general guidelines apply:

• Low carbon and HSLA steels: Suitable only for non-aggressive groundwater (pH > 7, low chloride and TDS). Their expected service life rarely exceeds 25 years.
• Type 304 stainless steel: Performs well in moderate water chemistries but should be avoided where chlorides exceed 300 mg/L.
• Type 316 and 316L stainless steels: Recommended for aggressive environments, providing superior chloride and temperature resistance.
• Duplex stainless steels: Best suited for high-pressure or saline applications, offering the highest combination of strength and corrosion resistance.

Material selection for water wells should follow a structured decision framework:

1. Characterize groundwater chemistry: pH, alkalinity, chlorides, sulfates, TDS, dissolved oxygen, temperature
2. Assess biological risk: Presence of iron bacteria, SRB, historical fouling issues
3. Define operational conditions: Pumping frequency, drawdown, flow velocity, idle periods
4. Evaluate design life requirements: Temporary vs. long-term infrastructure
5. Apply life-cycle cost analysis: Not initial cost alone.

When corrosion risk is uncertain or consequences of failure are high, conservative material selection favoring stainless steel provides predictable performance and risk reduction.

Municipal Wellfield Performance

A municipal wellfield in the southwestern United States provides a representative comparison of material performance. Wells completed in the 1980s with low carbon steel casing and screens began exhibiting significant drawdown increases and iron bacteria fouling within 10 to 15 years. Inspection revealed severe pitting at the static water level and extensive tuberculation along screen intervals. Rehabilitation cycles
shortened progressively until wells were abandoned after approximately 22 years.

Adjacent replacement wells installed using HSLA casing showed modest improvement, with the first major rehabilitation delayed to approximately 18 years. However, localized corrosion and MIC were identified as dominant failure mechanisms, particularly near screen slots and threaded connections. Service life improvement over LCS was estimated at less than 25%.

In contrast, wells completed with Type 316 stainless steel screens and casings have operated for more than 30 years with minimal loss of specific capacity.

This case history reflects performance trends documented across multiple municipal wellfields in the southwestern United States (Hanna et al. 2016; Badrak 2012a; Roscoe Moss Company 2004). Video inspection shows intact surfaces with limited mineral scaling and negligible pitting. Maintenance has been limited to periodic mechanical cleaning, confirming laboratory and field expectations regarding stainless steel performance.

Realistic Expectations for Material Life in Submerged Wells

Laboratory corrosion rates are useful for comparing materials, but they rarely translate directly into well casing service life. In real wells, corrosion is seldom uniform; it concentrates at welds, threaded joints, perforations, under deposits (scale/biofilm), and near the static water level where oxygen, temperature, and chemistry fluctuate.

A simple uniform wall-loss calculation can provide a baseline. For a 0.315-inch wall casing (315 mils), the time to through-wall penetration under uniform corrosion is thickness divided by corrosion rate. However, localized attack (pitting and crevice corrosion) often produces maximum penetration rates that are several times the average wall-loss rate.

To reflect field behavior, engineers commonly apply a pitting (localization) factor, defined as the ratio of maximum pit depth to average wall loss. Typical ranges for submerged service are 5 to 10 times for carbon/low-alloy steels, and one to two times for stainless steels when the passive film remains stable.

In chloride-bearing or stagnant crevices, stainless steels can experience localized pitting/crevice corrosion, so service life becomes chemistry- and design-dependent rather than rate-controlled (Van Droffelaar and Atkinson 1995; Clarke 1980).

Table 2 provides realistic life expectations for a 0.315-inch wall casing using measured immersion rates as a baseline and applying conservative localization factors to estimate time to first perforation. The field expectation column reflects typical industry experience in potable groundwater and highlights that localized corrosion, MIC, and differential aeration frequently control failure in carbon steels long before uniform thinning would predict.

Life-Cycle Cost Considerations

While initial material cost often dominates procurement decisions, life-cycle cost (LCC) provides a more accurate basis for evaluating water well materials (Hanna et al. 2016; McLaughlan 2002; Clear Creek 2003). LCC incorporates installation, maintenance, rehabilitation, downtime, and replacement costs over the service life of a well. Field studies demonstrate that corrosion-related failures drive the majority of unplanned well rehabilitation expenses.

Low carbon steel typically offers the lowest initial cost but the highest long-term cost due to frequent redevelopment, corrosion repair, screen replacement, and premature abandonment (Table 3). HSLA steels incur moderately higher initial cost but show only marginal improvement in corrosion performance,
resulting in similar long-term maintenance burdens. Stainless steels, particularly Type 316, have higher upfront costs but significantly reduced maintenance frequency and extended service life, often yielding lower total ownership cost over 30 to 50 years.

Conclusion

Corrosion performance, not mechanical strength, governs material suitability for water well construction. Low carbon steel and HSLA steels remain vulnerable to localized corrosion and microbiologically influenced corrosion under realistic groundwater conditions. HSLA offers only incremental improvement over LCS and should not be considered corrosion-resistant material.

Stainless steels represent a fundamentally different corrosion-control strategy through stable passive film formation. Among the materials evaluated, Type 316 stainless steel consistently provides the most robust performance across a wide range of groundwater chemistries, flow conditions, and biological environments. Although its initial cost is higher, reduced maintenance, extended service life, and lower risk of failure result in the lowest life-cycle cost for long-term wells.

For critical water supply infrastructure where longevity, reliability, and water quality are priorities, Type 316 stainless steel is the most technically defensible choice. Carbon and HSLA steels should be restricted to non-aggressive environments or applications where short design life and frequent maintenance are acceptable trade-offs.

References

Ahrens, E.H. 1966. Soil corrosion of low alloy steels. Journal of Materials Engineering 18, 3: 201–208.

Badrak, R.P. 2012a. Corrosion and materials for water well applications. Proceedings of the 3rd International Congress on Water Management in the Mining Industry: Santiago, Chile.

Badrak, R.P. 2012b. Corrosion and materials for water screen applications. NGWA Groundwater Summit: San Antonio, Texas.

Clarke, F.E. 1980. Corrosion and encrustation in water wells: A field guide for assessment. Food and Agriculture Organization of the United Nations: Rome.

Clear Creek Associates PLC. 2003. Sun City and Sun City West Wellfield Analysis, Surprise, Arizona

Edstrom Industries. 2022. Stainless steel and corrosion resistance: Material properties guide. Edstrom Technical Bulletin.

Hanna, T.M., Schnieders, M.J., and Schnieders, J.H. 2016. Operational Stage of the Well. National Ground Water Association Press: Westerville, Ohio.

Roscoe Moss Company. 2004. Increased Well Efficiency, Extended Lifetime and Reduced Maintenance through Selection of Stainless Steel Casing and Well Screen—Sun City and Sun City West, Arizona. Technical Memorandum.

Van Droffelaar H., and Atkinson, J. 1995. Metallurgical structures and corrosion behavior of water well materials. Materials Performance 34, 7: 46–52.

Zapffe, C. 1949. Development of stainless steels for corrosion-resistant applications. Journal of the Iron and Steel Institute 162: 145–152.

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Thomas M. Hanna, PG, is a technical director of water well products/hydrogeologist for Johnson Screens where he works in areas of well design, development, and well rehabilitation. He is a registered professional geologist in Arizona, Kentucky, and Wyoming and has worked for several groundwater consulting firms. Hanna can be reached at thom.hanna@johnsonscreens.com