Why Corrosion in Fire Protection Systems Demands Attention
Fire sprinkler systems are designed to operate reliably in an emergency — often after years or even decades of standing by. During that time, the internal environment of the pipework can change significantly. Corrosion develops gradually, and by the time visible signs appear, the damage may already be extensive.
Corroded pipes can develop pinhole leaks, blockages, and structural weaknesses that prevent a sprinkler system from performing as intended during a fire event. Beyond the immediate safety risk, corrosion leads to costly repairs, unplanned system downtime, and potential liability for building owners and operators.
Understanding the mechanisms behind corrosion — and knowing how to mitigate them — is therefore essential for anyone responsible for maintaining a fire protection system.
About the FM Global Corrosion Report
FM Global, a leading commercial and industrial property insurer with deep expertise in risk engineering, has published a detailed technical paper dedicated to corrosion in fire sprinkler protection systems. The report is widely regarded as one of the most thorough and authoritative resources available on this subject.
The paper covers both the analysis of corrosion causes and a range of practical mitigation strategies. It is intended to support fire protection engineers, facility managers, contractors, and insurers in making informed decisions about system design, installation, inspection, and maintenance.
The full report is available to download directly from the FM Global website, making it freely accessible to professionals across the industry.
Key Causes of Corrosion Identified in the Report
The FM Global report identifies several primary factors that contribute to corrosion within fire sprinkler pipework. Each of these factors can act independently or in combination, accelerating the rate of pipe degradation.
Pipe Welds and Corrosion Initiation
Welded joints are a common feature of steel fire sprinkler pipework, and the weld area can be a significant site of corrosion initiation. During the welding process, the heat-affected zone around the weld can alter the metallurgical properties of the steel, making it more susceptible to corrosive attack.
Poor weld quality, incomplete penetration, or the presence of weld spatter can create surface irregularities that trap moisture and contaminants. These localised conditions accelerate the electrochemical reactions that drive corrosion, often resulting in pitting that can penetrate the pipe wall over time.
Ensuring high-quality welds and conducting post-weld inspections are therefore important steps in reducing corrosion risk at these vulnerable points.
Residual Water in Dry Pipe Systems
Dry pipe fire sprinkler systems are designed to hold pressurised air or nitrogen in the pipework rather than water, with water only entering the pipes when the system is activated. This design is commonly used in environments where freezing temperatures could cause water-filled pipes to burst.
However, residual water — water that remains trapped in low points of the system after testing, draining, or activation — is a major contributor to corrosion in dry pipe systems. Even small volumes of standing water create a localised wet environment that promotes oxygen-driven corrosion and, in some cases, microbiologically influenced corrosion (MIC).
Proper drainage design, regular inspection, and the use of auxiliary drain points are essential practices for managing residual water and limiting its corrosive effects.
Air Entrapment in Wet Pipe Systems
In wet pipe fire sprinkler systems — where the pipes are permanently filled with water — the presence of trapped air is a leading cause of internal corrosion. Air introduced during system filling, maintenance, or repair contains oxygen, which acts as a primary driver of the corrosion process.
As oxygen is consumed by the corrosion reaction, it creates a differential aeration environment within the pipe. This accelerates localised pitting corrosion, particularly at points where air pockets form, such as high points in the pipework or areas with poor circulation.
Strategies to address air entrapment include careful system filling procedures, the installation of air vents at high points, and the use of nitrogen to purge oxygen from the system — a technique increasingly adopted in modern fire protection installations.
Microbiologically Influenced Corrosion (MIC)
One area that the FM Global report addresses with particular thoroughness is microbiologically influenced corrosion, commonly referred to as MIC. This form of corrosion is caused by the activity of bacteria and other microorganisms that colonise the internal surfaces of fire sprinkler pipes.
MIC can be especially aggressive, producing localised pitting that penetrates pipe walls far more rapidly than conventional corrosion. It is often found in systems with residual water, stagnant flow conditions, or where organic material has entered the pipework.
Identifying MIC requires specialist testing, and treatment typically involves biocide application, system flushing, and in some cases, pipe replacement. Early detection through regular water sampling and analysis is the most effective defence against MIC-related damage.
Corrosion Mitigation Strategies for Fire Sprinkler Systems
The FM Global report does not simply describe the problem — it provides a structured set of recommendations to help organisations mitigate corrosion risk across both new and existing fire protection systems.
Nitrogen Inerting
Replacing the air in dry pipe and pre-action systems with nitrogen significantly reduces the oxygen available to drive corrosion. Nitrogen inerting is one of the most effective and increasingly common mitigation techniques endorsed by fire protection engineers and insurers alike.
Corrosion-Resistant Pipe Materials
Specifying corrosion-resistant materials — such as stainless steel, CPVC, or internally coated steel pipe — during system design can dramatically extend the service life of a fire sprinkler installation. Material selection should be matched to the specific environmental conditions and water chemistry of each site.
Regular Inspection and Water Testing
Routine internal inspections, obstruction investigations, and water quality testing are fundamental to any corrosion management programme. These activities allow problems to be identified early, before they escalate into system failures or require extensive pipe replacement.
Proper System Design and Drainage
Good system design — including adequate drainage points, correct pipe gradients, and the avoidance of dead-leg sections — reduces the likelihood of water and air accumulation that drives corrosion. Reviewing existing system layouts against current best practice guidelines can reveal opportunities for improvement.
Accessing the Full FM Global Report
The FM Global corrosion report represents an invaluable resource for fire protection professionals seeking to understand and address corrosion in fire sprinkler systems. Its depth of analysis, combined with its practical recommendations, makes it an essential reference for engineers, contractors, facility managers, and insurers.
The full report can be downloaded free of charge from the FM Global website. Whether you are designing a new system, managing an existing installation, or investigating a corrosion-related issue, the guidance contained within this document provides a strong foundation for informed decision-making.
Taking a proactive approach to corrosion management is not just good engineering practice — it is a fundamental responsibility for anyone entrusted with the safety and reliability of a fire protection system.