man spark testing the external coating on a storage tank

High Voltage Spark Testing

Spark (Holiday) Detection uses high voltage electricity to locate any minute gaps in coatings.

Electrical high-voltage holiday detection is a simple method for testing coated or lined equipment using Holiday / Spark Test Detectors which are instruments that use electricity to locate film discontinuities.


Why Is Spark Testing Important?

Awareness of the environmental damage and safety implications of hydrocarbons leaking into the environment has been growing for a number of years.  Poorly fabricated tanks or corrosion of the steel used to make the tanks are the main causes of this. Corrosion-resistant steel such as stainless steel is one option to address this but the increased material costs make this solution unviable. In response to these concerns manufacturers of underground tanks have worked with coatings specialists to develop coatings specifically designed for this application. In addition, a worldwide standard for the manufacture of underground tanks (EN 12285-1) was created to ensure best practice was being applied and to give customers the confidence of knowing their tanks, regardless of manufacturing location were being produced to a common standard.

Creating an impervious layer around the outer skin of the tank preventing corrosion is a critical part of this standard. Many coating may appear to give this protection but in fact, can contain small “pinholes”  or voids that will allow moisture to penetrate to the steel skin. To ensure this does not happen with the coatings we use “Spark Testing” after the tanks are coated to confirm the coating has created an impervious layer.

How Does High Voltage Holiday Testing Work?

The vast majority of coatings and linings are poor electrical conductors and as such act as insulators. However steel items are conductive to electricity.

A spark test detector consists of a power source, a ground wire, an electrode (typically a drum brush type), and an indicator. Current flows if the leads of the ground wire and the electrode are attached to the power source and their tips are touched. When the ground wire is connected to an uncoated part of a coated piece of steel and the electrode is placed on the coated surface, the coating acts as an insulator and no current flows. However, if a pin hole is present in the coating, there is a pathway for the current to flow. The spark detector has indicators both audible and visual to reveal when current is flowing and a defect located.

If a defect is detected it is repaired and re-tested before dispatch.