Screening Tests for Evaluating the Effectiveness of Gypsum Scale Removers - Item No. 21230

Abstract

General

The two test methods described in this standard are static laboratory screening tests designed to measure the ability of chemicals to remove gypsum scale deposits.

The first method is a single-stage dissolver process in which the test agent dissolves the gypsum solid.

The second method is a two-stage process where the test agent converts the gypsum to an acid-soluble salt, and this salt is dissolved using an HCl solution.

Both methods should be performed, and should use the same original form of gypsum to make economic and performance decision on which method and chemicals are most appropriate for each field situation.

There are two types of scale-removal chemicals: dissolvers and converters.

Scale dissolvers, generally chelating or sequestering agents, can affect the dissolution and removal of gypsum scale in one step.

Converters, such as those formulations based on sodium (or potassium) glycolate and sodium (or ammonium) carbonate (or bicarbonate), are used to alter or convert the calcium sulfate to another compound which is then removed by dissolution with a dilute mineral acid (typically hydrochloric acid).

Test methods for screening both gypsum scale dissolvers and converters are described.

The purpose of this test method is to provide an approach for users to compare 1) their scale dissolvers against EDTA, a standard dissolver chemical and 2) their scale converter against potassium glycolate, a standard converter chemical.