Water Well Journal
Issue link: https://read.dmtmag.com/i/557876
The nail test, a simple method for corrosion evaluation. Heavy deposit buildup, resulting in corrosion damage to well components. Well filter pack material evaluated in comparative research. from potential deposit formation and resulting maintenance requirements. Correspondingly, mineral and bacterial deposition in the well can have an ad- verse effect on the produced water quality from mineral concentrations or sluffing of organic biofilm. These ef- fects on water quality can cause changes to the planned treatment process. The Saturation Index is used for pre- dicting if the water is corrosive or scale- forming from a calculation including temperature, total dissolved solids, cal- cium concentration, total alkalinity, and pH value. Evaluating concentrations of chlorides, carbon dioxide, and dissolved oxygen in the water can also assess the corrosion potential. Total organic car- bon concentrations are indicators for potential bacterial accumulation and the residual effects of system fouling and microbial-induced corrosion. In a bacteria assessment prior to well construction, it is difficult to predict the biofilm potential. However, knowledge of the organisms present and the bacter- ial load can be beneficial in the evalua- tion for material needs. Potential well maintenance and reha- bilitation equipment, chemicals, proce- dures, and physical clearance issues including two-piece wells should be considered. Cleaning chemistries are generally acid-based compounds and disinfection products are often strong oxidizers. Both present corrosion poten- tial to some materials. Of all the factors affecting well con- struction material selection, corrosion potential is the most apparent. The vari- ety of sources for corrosion offer a wide range of issues that must be taken into account within the material selection process. In the galvanic corrosion activity, anode-cathode-electrolyte ion transfer phenomenon, the issue of dissimilar metals used in the well construction along with a strong electrolyte, the aquifer water, can produce the loss of metal ions from the anode to the cath- ode—resulting in corrosion damage to the anodic metal. The Saturation Index is the first step in evaluating the potential for galvanic corrosion by assessing the water chem- istry. This, in addition to the galvanic series of metals, can guide in making proper material selections. As the Saturation Index requires lab- oratory analysis, a simple corrosion test is available, the nail test (Schnieders 2009). This test uses a cup of the aquifer water and a low carbon steel 6 penny nail submersed for 24 hours. The test is observed for the presence of a pink color in the water indicating metal oxi- dation or corrosion. Concentration cell corrosion which occurs where deposits are present, also referred to as "under deposit corrosion," creates a localized pitting type of damage. Impingement attack corrosion is caused by physical and chemical con- ditions occurring within the moving water. High suspended solids in the aquifer water can be an indicator of this problem and gas/air bubbles can cause cavitation within the pump. The contin- ual collapse of bubbles on the metal sur- face of the pump impellers creates the impingement damage. The selection of stronger metal components or metal- lized surfaces can inhibit this damage. Microbial-induced corrosion (MIC) is difficult to predict as previously noted but is an important factor in the life of a well. The presence of iron-oxidizing bacteria or acid-producing organisms in high numbers can be an indicator of future problems from MIC, fouling, and associated deterioration. In review of common well construc- tion materials and their effects on deter- ring the issues noted, the comment should be made in regards to corrosion there are various systems and technolo- gies available such as protective coat- ings, cathodic protecting systems, and sacrificial anode assemblies to consider. Casing component The primary components of a water well structure, casing, screen, and filter pack material provide the major area of consideration for proper material selec- tion that can impact the full life cycle cost of a well. Casing and screen com- ponents are generally available in steel, PVC, and to some degree, HDPE and fiberglass. Steel casing and screen components for water wells basically fall into three categories: low carbon steel, high CRITERIA from page 21 waterwelljournal.com 22 September 2015 WWJ