October 8, 2009

Testing of Coatings and Linings in Wastewater Environments

by Bob Murphy

New coating and lining formulations are being developed to meet current performance needs and also future environmental regulations. The time is takes from original concept to possible formulation to commercialization is being compressed. Evaluation of the new formulations for coatings and lining used in harsh wastewater environments can be a daunting task. The standard practice has been to have 5-10 years worth of field use before a product can be approved. Today, coating formulations can be tested using accelerated methods that may approximate actual field conditions.

Laboratory and field performance testing can provide the specifier with valuable data, which forms the basis for responsible material choices. Comprehensive testing of coatings and linings for wastewater environments can provide a means to compare materials based on analytical data and well as field experience.

The question arises, what test methods and their results are truly applicable?

Key Physical Testing Methods

Compressive Strength: ASTM C-579 “Test Method for Compressive strength of Chemical Resistant Mortars and monolithic Surfacers”

Compressive loads are usually not an issue in wastewater structures. This method can be used when using “filled” coatings than can form a monolithic coating over a substrate.

Abrasion: ASTM D-4060 “ Test Method for Abrasion Resistance of Organic Coatings by Taber Abrasion” The surface is abraded by a rotating a coated panel under weighted abrasive wheels. Abrasion resistance is usually expressed as the loss of coating weight in milligrams at a specific number of cycles under a specific abrasive wheel. This test method has poor reproducibility between labs, so testing should be restricted to one lab and a control used if possible.

Permeability: Permeability is a material property, which defines the ability of molecules of water vapor (i.e. corrosive chemicals, sulfides etc.) to penetrate through the coating/lining and therefore be able to begin to attack the substrate. The two most common methods are ASTM E96 / E96M – 05 Standard Test Methods for Water Vapor Transmission of Materials and ASTM D1653-93 Standard Test Methods for Water Vapor Transmission of Organic Coating Film.

Chemical Resistance: Municipalities such as the City of Houston, LACSD and MWRA have undertaken testing programs that have tested a wide range of chemicals including sulfuric acid, sodium  hypochlorite, sodium hydroxide, soaps  and so on. This testing when combined with third party testing programs can lead to an increased level of confidence in coating/lining performance for the specifier and owner.

A coating/lining system that exhibits good chemical resistance, excellent abrasion resistance and resistance to permeation when properly installed and inspected can achieve long term asset protection

Comments

  1. October 27th, 2009 at 6:10 am

    Dear Sir,

    For a big project for sewage channel lining we suggest poly urea, do you know poly urea used in sewage channel till now for a big channel or No? and if this lining can resist against negative pressure of water or No?
    In advance thank for your cooperation

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