Float operations of almost any size need to include some type of meaningful test plan. The plan should evaluate materials, finishes, applications and inspection procedures. In the absence of extensive historical field performance data, such plans are an objective basis for determining future work. These can be done in-house or contracted with a number of consulting/inspection companies to assist those who do not have the necessary staff.
REMEMBER: All parties interested in this work are in favor of developing the plan and agree upon the basis on which the decision is made.
Whenever possible, standard testing procedures and evaluation methods provided by NACE International, ASTM, SSPC, etc. should be consulted and followed. Only then can correlations with other workers' results be established. The tests described below are typical for coatings subjected to atmospheric exposure; however, the general method for buried or immersed coatings is similar in most respects.
lab testing
The number and types of tests that can be performed in a laboratory are virtually limitless. Because on-site testing of coatings is so expensive in terms of time, labor, and facilities, an ongoing goal for formulators, raw material producers, and coating users is to establish meaningful accelerated testing. These may involve a wide variety of procedures, ranging from relatively simple to highly complex.
Testing can define certain characteristics of a coating system. This distinction is usually specific to the type of accelerated test and usually does not indicate in advance how a given coating will perform in service. However, these tests are invaluable when developing coatings or evaluating new concepts for coating applications or use.
Field or Service Test
While in many cases the delays involved in field or service testing seem insanely long (it can take years to complete a full field test)) when coating expenditures run into the hundreds of thousands of dollars, and in some cases millions of dollars , it pays to ensure performance. Most field testing is done on site under the supervision of customer Testers. Typically, as a first step, the test specimen coated with the material to be tested is exposed multiple times at several test sites in the plant.
After various exposure times, according to the design of the test program, the specimens are removed from the exposure location to the laboratory where their residual properties are measured. At the end of such a procedure, very good performance can usually be identified from a similarly exposed set of coatings. This coating can be confident that it will receive good service.
As with any other testing, field test panels and applications should be chosen to represent common situations or other conditions of interest.
Once panel testing is complete, the usual procedure is to apply two or three promising material candidates to tanks or other large metal areas at the factory site, fully aware that all surfaces on site are highly Far from the same exposure. The four quadrants of the tank are different in sunlight exposure, and the top and bottom halves of the tank are different due to internal variations in liquid level.
In any large chemical or industrial plant, one plant location can be orders of magnitude more or less corrosive than another. Therefore, exposure at a single location may not give results that can be confidently expected everywhere in the plant. Also, since some locations are less corrosive, they may not require as expensive systems as those used in very aggressive locations.
This article was adapted by MP Technical Editor Norm Moriber from Corrosion Basics—An Introduction, Second Edition, Pierre R. Roberge, ed. (Houston, TX: NACE International, 2006), pp. 449-452.
