More and more frequently, engineers are called out to instances where steel tanks have become victims of corrosion and rusting, which is generally due to chemical or electrochemical reactions between a tank and the environment.
The oil industry is certainly no exception, with corrosion seen as a major cause of expensive equipment failures and reduced operational functionality. For example, in 2018 the UK experienced an extremely cold winter which was followed by an incredibly dry summer. This led to a 23% rise in callouts to instances of corrosion and reports of fuel contamination.
More often than not, steel tanks are used to store bulk amounts of fuel due to their preferable characteristics when compared to plastic tanks. They are a sturdier option for fuel storage so are able to withstand more impact when onsite and they are generally non-porous, meaning they will not absorb any of their contents.
Unfortunately, despite their comparable strengths, steel tank properties also mean that they are more prone to corrosion from weather conditions, such as UV light, heat and condensation. Water in fuel tanks is particularly common during spring and summer due to heat gain and evaporation. When the temperature increases, condensation forms internally and causes the tank to breathe. This exacerbates contamination and causes water and bacterial microbial contamination to build up.
Corrosion forms from the inside out, so the extent of the problem is not generally known until external problems manifest, which can often be too late to rectify. As a rule, diesel fuel should be stored for no longer than six months without being checked by fuel testing to ensure that it meets specification before it is used.
In a 12-month period, Crown Oil Environmental was called out to 482 instances of corrosion. The vast majority of these cases could have been avoided by regular checks, simple tank maintenance and keeping fuel levels to a maximum to reduce the risk of moisture.
There are several types of corrosion, including: general, local, pitting and weld metal corrosion. General corrosion occurs throughout a tank whereas local corrosion appears in specific areas where water collects or flows. Pitting is found along horizontal surfaces, the bottom of tanks and where water accumulates. Once pitting corrosion becomes thicker than one-third of the wall depth, it manifests as a problem. Weld metal corrosion occurs when welding metal interacts with metal in the fuel tank, triggering an electrolytic action.
Written by Chris Beatty, Crown Oil Environmental, UK.
Read the article online at: https://www.tanksterminals.com/special-reports/07032019/combatting-corrosion/