Corrosion of Agriculture Equipment
All this makes corrosion a key issue in agriculture, even though it is often not given the importance it deserves.
How does corrosion affect the agricultural industry?
Agricultural chemical & biological products
Fertilisers – Some fertilisers have very corrosive decomposition by-products, such as ammonia, hydrogen sulphide or chlorides (including potassium or ammonium chloride).
Silage – is high-moisture fermented forage, used as food for ruminants. It undergoes fermentation over approx. 2 weeks from the time it is stored in the silo. In the process it releases a nitric-bearing corrosive liquid.
Herbicides and pesticides – often contain copper-bearing fluids. For example, the “Bordeaux Mixture” is made from copper sulphate, water and lime, which attacks aluminium and zinc, thereby eroding the protective galvanic layer from equipment and structures made of galvanised steel.
Slurries and manures – Slurry is a mixture of animal dung and urine, and manure is slurry composted with straw, wood shaving and other waste. They have corrosive constituents, such as uric acid, ammonia, ammonium salts, and naturally excreted chloride.
Structures
Agriculture makes prolific use of steel structures and sheet-metal walls and partitions. As mentioned above, many agricultural chemical and biological substances are corrosive. Also, the environment takes its toll, especially in locations close to the sea or with high ambient humidity. Condensation is always a problem in humid climates having marked temperature differences between day and night.
Much of the steel used is galvanised. However, corrosive substances, whether salt or acidic by-products erode the protective galvanic coating, exposing the underlying steel to corrosion. For example, in rural inland areas, a galvanised sheet-steel wall may last over 30 years without preventive maintenance, whereas in a humid or polluted environment, it would last 5 to 10 years.
Additionally, certain soils (sulphate and chloride bearing peats and marshes) attack structure foundations.
Silos are damaged by organic acids – A very acidic and corrosive environment prevails in silos containing crop maize silage, which rapidly ferments, producing acids with a typical concentration in solution of 2% lactic acid, 0.5% acetic acid, and a pH as low as 3.6.
Dairy farming infrastructure – Milking equipment is generally made of stainless steel, which has excellent corrosion withstand. However, supporting structures, made of mild steel, are prone to corrosion by lactic acid- bearing milk wastes and chlorine-bearing cleaning/sterilisation agents.
Machinery & equipment
Agricultural activity is seasonal, different machines being used in different seasons. Machines are stored away, sometimes for months on end, when seasonal activity (or inactivity) does not require their use – especially during cold humid winters. If they are not thoroughly cleaned before storage, the residue of the substances they handle will surely cause corrosion over the months.
Machines that handle chemicals are the most vulnerable to corrosion, in particular those handling slurries and artificial fertilisers, which are highly corrosive, as already mentioned.
Poorly drained areas and inner machine structures, where chemicals, dirt and moisture can accumulate are particularly vulnerable to corrosion. High humidity (leading to condensation) and poor ventilation of the hangars where machinery is stored off-season accelerates any corrosion process, sometimes significantly.
Which parts of the machinery are the most vulnerable to corrosion? The inner surfaces of metal containers and piping which handle corrosive substances, overlapped joints, spot-welds, or any other crevices, as well as moving parts, e.g. cutters, feed mechanisms, bed chains, hinges.
What are the consequences of corrosion in agriculture?
Corrosion reduces the metal thickness of structural elements, which leads to a loss of mechanical strength and the risk of structural failure – with the attendant risk of causing injury to people, animals and/or spillages.
Leaks caused by corrosion can lead to fluids stored in vessels or flowing in pipes to be contaminated by foreign substances.
Leaks also cause spillage, and consequent damage to surrounding equipment, to animals, and/or to the environment.
Pumps and valves may suffer damage from solid corrosion products carried by the fluid which they handle.
And how much is corrosion costing the agricultural industry?
According to the US National Agricultural Statistics Service, there are approx. 1.9 million farms in the USA, and the value of farm machinery and equipment is estimated to stand at $15 billion annually (1997 census). It was found that the two principal reasons for replacing machinery and equipment were the upgrade to more modern equipment and the replacement of worn-out and corroded equipment.
According to the NACE publication “Corrosion Costs and Preventive Strategies in the United States – publication no. FHWA-RD-01-156”, released by the U.S. Federal Highway Administration (FHWA) in 2002:
The corrosion cost in the US agricultural industry is estimated to be $1.1 billion, based on the assumption that corrosion costs represent 5% to 10% of the value of all new equipment.