This next article in our Mechanical Integrity (MI) series focuses on storage tank integrity, an area often underestimated due to the perceived low-pressure nature of tanks, yet one that's been responsible for several high-severity fires, spills and business interruption events. This article highlights how seemingly low-risk equipment can lead to major consequences.
Atmospheric storage tanks are widely used across industrial facilities to store hydrocarbons, chemicals and intermediate products. Common tank types include fixed roof, floating roof (internal and external), and specialty tanks designed for specific services.
While storage tanks operate at relatively low pressure compared to pressure vessels, they often contain large inventories of flammable or hazardous materials, making them among the most significant contributors to a site's fire and spill risk profile.
Failures in storage tanks are typically:
- Slow to develop but severe in consequence
- Environmentally impactful (large spills resulting in soil and groundwater contamination)
- Triggers for a domino effect (pool fires, bund fires, multi-tank involvement)
- Costly, with significant clean-up, repair and business interruption implications
From an insurance perspective, storage tank failures can drive high-value loss scenarios, particularly when fire or tertiary containment failure occurs.
Why does storage tank integrity require special attention?
Storage tanks present distinct integrity challenges:
- Large surface areas exposed to corrosion (internal and external)
- Bottom plates in continuous contact with soil or water ingress
- Susceptibility to settlement and foundation-related issues
- Vapour space hazards (flammability, overpressure, rim seal fires)
- Relatively long inspection intervals with limited online visibility
Degradation in tanks can remain undetected for extended periods, particularly at the tank bottom and underside, where inspection is most difficult.
A practical self-check: Are your storage tanks truly under control?
The following self-checks can help quickly assess whether your mechanical integrity program is effectively managing the inherent risks.
1. Are you effectively managing tank bottom integrity?
Tank bottoms are one of the most critical and failure-prone components due to corrosion from both internal contents and external soil-side exposure.
Ask yourself:
- Are appropriate inspection techniques being applied for the tank bottom assessment (e.g., Magnetic Flux Leakage or Saturated Low Frequency Eddy Current)?
- Are tank bottom inspection intervals risk-based, justified and aligned with actual degradation rates?
- Are water draw-off practices effective in minimising internal corrosion risk?
2. Are settlement and foundation conditions actively monitored?
Foundation issues can lead to shell distortion, bottom plate stress and eventual failure if not detected early.
Ask yourself:
- Are settlement surveys conducted periodically and compared against allowable limits and are pass/fail criteria clearly defined?
- Are tilt, edge settlement and differential settlement routinely measured?
- Are drainage and foundation conditions maintained to prevent water ingress? Is water accumulation or soil erosion around the foundation promptly identified and rectified?
3. Are floating roof and rim seal systems properly maintained?
Floating roofs are critical for vapour control and fire risk reduction. Failures in seals or roof systems can significantly increase vapour emissions and ignition risk.
Ask yourself:
- Are rim seals regularly inspected and maintained?
- Are roof drains, pontoons and deck integrity checked for leaks or damage?
- Are gaps or seal degradation promptly addressed?
4. Are overfill protection and level control systems reliable?
Overfill remains one of the most common causes of major tank incidents, often leading to large spills and fires.
Ask yourself:
- Are independent high-level alarms and shutdown systems installed?
- Are these systems tested periodically and independently of the basic control system?
- Are filling procedures and operator responses clearly defined?
Final thoughts
Although storage tanks operate at low pressure, their large inventories and fire potential mean they carry a significant level of inherent risk.
Across higher-performing sites, we typically observe:
- Strong focus on tank bottom integrity and corrosion monitoring
- Active monitoring of settlement and foundation conditions
- Robust maintenance of floating roof and sealing systems
- Independent and tested overfill protection systems
- Conservative decision-making around inspection intervals and deferrals
Our next article will delve into the challenges associated with ensuring the integrity of heat exchangers. These are common pieces of equipment across high-hazard industries that present unique challenges in ensuring mechanical integrity.
Gallagher is the third-largest broker in the world and is committed to supporting risk management best practice across the Energy Industry. For more information about our in-house risk engineering and risk advisory services and how we can support you, please reach out to our team.