Knowledge base
Steel tank corrosion — causes, symptoms, and what to do next?
Corrosion is the most common cause of steel tank failure. Learn to recognise the symptoms, understand the consequences of neglect, and know when it pays to repair — and when to replace — a tank.
Corrosion by the numbers
That is what corrosion costs in industrialised countries — according to NACE International data.
The average carbon-steel tank without adequate corrosion protection.
Stainless-steel tanks or those that are regularly serviced can last significantly longer.
The estimated share of storage-tank leaks attributable to corrosion processes.
Types of steel tank corrosion
Steel tank corrosion is not a uniform phenomenon. Uniform corrosion causes a gradual, even loss of material across the entire surface — it is the easiest type to predict, yet it often goes unnoticed until the wall has been critically weakened.
Pitting corrosion is a far more insidious form. It creates small but deep cavities that can perforate the tank wall before the overall visual condition raises any concern. It is particularly dangerous in tanks storing chemically aggressive media.
Crevice corrosion occurs at points of contact between components — under gaskets, at welds, and around nozzles. Galvanic corrosion occurs when a tank is connected to pipework made of a different metal without adequate electrical isolation.
Corrosion can progress from the inside (contact with the stored medium) or from the outside (moisture, atmospheric conditions, lack of insulation). Correctly identifying the type of corrosion is essential for choosing the right repair method or deciding whether to replace the tank.
Early warning signs
Identifying corrosion at an early stage allows you to avoid a costly failure. Here are the most common symptoms to watch out for:
Visual changes: rust streaks on the outer surface, blistering and delamination of the protective coating, discolouration around welds and nozzles. Even minor rust spots can indicate advanced corrosion beneath the surface.
Leaks and moisture: damp patches at the base of the tank, traces of moisture on insulation, the smell of the stored medium in the vicinity of the tank. Any leak, however minor, requires an immediate response.
Changes in the quality of the stored medium: cloudy water, mechanical contamination, changes in odour or taste. If the medium's properties are changing, the cause may be corrosion inside the tank.
Wall-thickness measurement results: regular ultrasonic measurements allow material loss to be detected far earlier than visual inspection. This is the most effective method of monitoring the technical condition of a tank.
Consequences of ignoring the problem
Dismissing the first signs of corrosion almost always leads to escalation of the problem. Emergency leaks mean not only the loss of the stored medium, but often contamination of the soil and groundwater — which entails criminal liability and remediation costs running into hundreds of thousands of złoty.
In the case of pressure tanks, corrosion weakening the wall creates a direct risk to human life. A tank rupture under pressure is a catastrophic scenario.
Unplanned production downtime, the need for emergency emptying and tank replacement, and penalties for breaching environmental regulations — these are real costs that can be avoided through systematic inspection and proactive replacement.
The UDT may order the immediate withdrawal of a tank from service if its technical condition poses a hazard. Resuming operation then requires completing the full acceptance procedure for the new equipment.
Repair or replace? Decision criteria
The decision between repairing and replacing a tank depends on several factors. Repair makes sense when corrosion is superficial and localised, wall thickness remains within the standard, and the tank is relatively new.
Replacement is necessary when corrosion losses exceed the permissible minimum wall thickness, corrosion is extensive or multi-focal, the tank is approaching the end of its planned service life, or when the cost of repair exceeds 40–50% of the price of a new tank.
It is worth considering preventive replacement with a stainless-steel tank or a double-walled tank — particularly when the stored medium is chemically aggressive or poses an environmental hazard. The higher upfront cost pays back quickly thanks to years of trouble-free operation.
When replacing a tank, it is worth consulting the manufacturer on the choice of material and design best suited to the specific application. A tank designed with the properties of the medium and operating conditions in mind will deliver a significantly longer service life.
Corrosion prevention methods
Selecting the right material is the most effective form of protection. Stainless steel (AISI 304, 316L) eliminates corrosion problems in most applications. Acid-resistant steel is essential for chemically aggressive media.
Protective coatings — both internal (laminates, epoxy paints, rubber lining) and external (paint systems, galvanising) — extend the service life of carbon-steel tanks. The quality of surface preparation before applying the coating is critical.
Cathodic protection — galvanic anode or impressed-current systems — is particularly effective for underground tanks and installations exposed to soil corrosion.
Regular inspection and maintenance — annual visual inspections, periodic ultrasonic testing, and timely renewal of protective coatings. The maintenance plan should take into account the specific properties of the medium, environmental conditions, and the manufacturer's recommendations.
For tanks storing hazardous substances, an additional layer of safety is provided by a double-walled design with an interstitial space leak-monitoring system.
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