Holiday detection: No room for coating defects

A holiday, as it’s called in industry jargon, might sound like a break, but in pipe coating, it’s the last thing you want. A small imperfection can lead to corrosion, paving the way for leaks, environmental damage and costly repairs. This article explains how holiday detection helps identify coating defects before they become a problem.

The term “holiday” originates from shipbuilding. If a painter accidentally missed a spot, part of the hull remained unprotected. They called it a holiday. Not because they were celebrating, but because the painter clearly needed one.

Today, the stakes are much higher. Just as an uncoated wooden ship could rot and sink, an undetected flaw in a modern pipeline coating can eventually lead to corrosion and pipeline failure.

What is holiday detection?

Holiday detection is one of the final quality checks before a coated pipe leaves the production line. The process identifies defects in the protective coating before they become a problem.

During the inspection, a holiday detector applies between 2 kV and 30 kV to the coated pipe. If the coating is intact, it insulates the steel and no current flows. If there’s a defect, the current reaches the steel and immediately triggers an alarm.

Holiday detection also helps prevent issues such as cathodic disbonding, where the protective coating loses adhesion and leaves the steel vulnerable to corrosion.

No room for guesswork

If there’s a gap in the coating, it needs to be detected before the pipe leaves the production line. That’s why the machine’s signals leave no room for doubt. As Jan Peter Biersteker, Sales Director LINEPIPE Division, explains: “At that moment, it’s alert mode in the factory! WEE-OOO WEE-OOO and flashing light.”

Why early detection matters

A holiday means the protective layer of a pipe isn’t doing its job. In industries such as oil, gas, hydrogen and CO₂ transport, coating defects simply aren’t an option. Pipelines are expected to operate safely for 30 to 50 years, making reliable coating inspection essential.

Early holiday detection helps to:

• Prevent corrosion before it develops into leaks.
• Avoid costly repairs and downtime. On offshore pipelay vessels alone, delays can cost millions per day.
• Reduce the risk of failures after installation.
• Protect long-term pipeline integrity.

A pipeline is only as strong as its weakest link. One coating defect can have major consequences.

Real-world challenges

Holiday detection sounds straightforward, but in practice it requires speed, precision and immediate decision-making.

Pipes continue moving through the production line while inspections are carried out. If a test fails, operators often have only minutes to decide whether a coating should be repaired locally or recoated.

The challenge becomes even greater on offshore pipelay vessels, where coated pipes are welded together before being lowered into the sea.

As Jan Peter explains: “Re-coating an entire pipe is a massive job. And since our coatings are built to last for decades, removing them isn’t exactly a casual afternoon task. That’s why, in many cases, fast, local repairs are the best option.”

Tailored to every project

No two production environments are exactly the same. Some projects require fully automated inspection systems capable of scanning an entire pipe within seconds and providing immediate feedback.

That’s why Selmers develops holiday detection solutions tailored to each production environment, helping customers combine speed, accuracy and reliability throughout the coating process.

The final quality check

As one of the final quality checks before a pipeline enters service, holiday detection helps identify coating defects before they become costly problems. Detecting imperfections at the right moment helps prevent repairs later and supports safe, reliable pipeline performance for decades.