What is a pipeline blister?
A pipeline blister is a void located near the surface of a steel pipe that is surrounded by a thin layer of metal. These defects typically occur during manufacturing. While blisters themselves are not usually a structural problem, they can create weak points that may lead to other issues over time.1,2
How do pipeline blisters occur?
Pipeline blisters usually form during the manufacturing process, when gas is trapped in the steel as it solidifies. Common causes include laminations, inclusions, or other hydrogen traps. Hydrogen can enter the steel of a pipeline when corrosion occurs inside the pipe, or when chemical reactions take place outside the pipe. These hydrogen atoms migrate through the metal and accumulate in tiny cavities, where they combine to form hydrogen gas. As more gas accumulates, the pressure inside the cavities increases, causing the blister to grow and separate the layers of steel. This process continues until the blister reaches solid metal, at which point it may split open. Depending on the pipe’s condition, a sufficiently large blister can weaken the pipe wall, leading to leaks or even a complete rupture.2
What are the risks of pipeline blisters?
Although small blisters do not usually pose a direct threat to pipeline integrity, they can lead to subsequent problems.
For example:
- Corrosion initiation: If the cavity becomes contaminated, it can initiate pitting corrosion.
- Coating damage: Blisters can create “holidays” (gaps) in protective coatings, compromising corrosion protection, unless they are removed before the coating is applied.
- Structural failure: Large blisters that burst can weaken the pipe wall, potentially causing leaks or ruptures under pressure.1,2
Explore more on this topic
Pipeline Corrosion Management
Understanding pipeline corrosion is the first step – assessing and managing it is the next. Discover how our corrosion assessment solutions support pipeline safety.
The Competence Club
Looking to build practical knowledge beyond the Encyclopedia? Join The Competence Club to access exclusive learning modules, expert insights, and technical guidance on pipeline safety, defect assessment, and more.
Source reference
- The Encyclopedia of Pipeline Defects, ROSEN UK, Edition 3, 2017.
- Managing Pipeline Threats, John Tiratsoo, 2019.