Nonvisible Contaminants on Railcar Surfaces
|Publication Date:||1 August 2014|
Coating manufacturers and the contracting authority have an interest in establishing the parameters that define satisfactory performance of specified coatings.
Therefore, soluble-salt removal requirements sometimes are included in the job specification. The fact that no field method is considered to capture 100% of the salts from a surface continues to hamper efforts to establish acceptable levels of salt contamination under coatings. It is beyond the scope of this report to designate specific numeric levels. Coating manufacturers may be able to give some insight as to what nonvisible salt levels are acceptable for their products.
Shortened coating life has often been attributed to errors in the selection of material, formulation, surface preparation, coating application, or an additional contributor such as nonvisible surface contaminants (NVSC).
New and used steel surfaces can become contaminated during manufacture, transport, storage, and fabrication, from the environment, or surface preparation, or by lading in the case of railcars. Also, a railcar's prior service is often a key contributor to surface contamination and corrosion.
NACE and SSPC(1) joint surface preparation standards1-9 are based on visual examination without magnification. Visible contaminants are not addressed in this report. Surfaces typically are prepared to an appropriate visible standard; however, they may still contain a level of NSVC.
The components usually considered key to determining the potential or rate of failure for coatings applied to railcar steel surfaces as a result of NSVC are as follows:
- The contaminant and the quantity of contaminant remaining on the surface to be coated;
- The coating system to be applied; and
- The future exposure to contaminants as a result of services (lading).