Agricultural Machinery Corrosion

Abstract

Agricultural machinery expose to wear and corrosion. This damage results from dealing with varying conditions, such as plant moisture, density of plants, soil types, and environmental condition in the field; therefore, this damage leads to an increase in energy consumption, production losses, and a decrease in the lifetime service of reciprocating mower knives. There are many studies that have identified solutions that can be used to increase the life span of agricultural machinery by reducing the chemical corrosion of agricultural machinery. The methods used to reduce chemical corrosion in agricultural machinery can be summarized by selecting new resistant materials, using paint, and using corrosion inhibitors.

1. Introduction

Agricultural mechanization plays an important role in achieving many United Nation’s sustainable development goals, especially the first goal (no poverty) and second goal (zero hunger) [1]. Agricultural mechanization can help the sustainable development of world food systems by increasing output production and reducing lost foods through the production chain [2]. Agricultural mechanization covers the manufacture, use, maintenance, and repair of machines used in agricultural production (crop and livestock) and postharvest process [3]. Agricultural machinery is working in special and hard conditions, where it deals with different kinds from the environment, soil, plants, pesticide, fertilizers, harvesting, and postharvest processing due to the reaction between agricultural machines and these conditions lead to exposure to wear, such as adhesive, abrasion, fatigue, erosion, chemical, and corrosion [4, 5].

1.1 Corrosion phenomena in agricultural machinery

Corrosion is the surface disintegration of metals/alloys within a specific environment. Some metals basically exhibit high corrosion resistance than others and this can be attributed to several factors like their chemical constituents, the nature of electrochemical reactions themselves, and others [6]. All machines and mechanical systems have moving parts from different materials, so wear is the biggest problem in the industry [7]. In addition, Figure 1 explained the effect of different conditions on agricultural machinery wear [8].

Figure 1.

Corrosion in agriculture machinery [8].

1.1.1 Corrosion cost in agricultural machinery

Hou [9] pinpoints the cost of corrosion in the world is about 2505 billion dollars and this represents 3.4% of the gross national product (GNP) as shown in Table 1. In addition, the effective control of corrosion (coatings, new materials, and preventative maintenance) is estimated to reduce this cost by 15–35% or as much as 875 billion dollars annually [10, 11]. The cost of wear and friction in Turkey is decreased by 337 million dollars due to improving the material used in the industry against corrosion and wear [12, 13].

Economic regions	Corrosion cost of agriculture US$ billion	Corrosion cost of industry US$ billion	Corrosion cost of services US$ billion	Total corrosion cost US$ billion	Total GNP US$ billion
United States	2.0	303.2	146.0	451.3	16,720
India	17.7	20.3	32.3	70.3	1670
European Region	3.5	401	297	701.5	18,331
Arab World	13.3	34.2	92.6	140.1	2789
China	56.2	192.5	146.2	394.9	9330
Japan	0.6	45.9	5.1	51.6	5002
Four Asian Tigers plus Macau	1.5	29.9	27.3	58.6	2302
Rest of the world	52.4	382.5	117.6	552.5	16,057
Global	1527	1446.7	906.0	2505.4	74,314

Table 1.

Global cost of corrosion by region by sector [10].

There are about 1.9 million farms in the USA that produce livestock and crops. All these farms have a big problem with the cost of replacing machinery and equipment due to wear and corrosion. The cost of this problem in the agriculture sector was estimated to be 1.1 billion dollars, as shown in Figure 2 [14]. In addition, in China, the cost of corrosion in the agriculture machine sector was 1.38 billion dollars as 2.5% of the total estimated value of the agricultural machinery industry [9].

Figure 2.

The corrosion cost in production sectors [14].

Agricultural machinery refers to the machines used in plant production and husbandry production as seedbed preparation machines, plating machines, protection machines, harvesting machines, processing machines, livestock machinery, and agricultural transport machinery. At present, there are about 3500 kinds of agricultural machinery products in China [15]. Repair and maintenance are necessary for keeping machine parts with minimized effect wear, part failures, accidents, and natural deterioration. Moreover, the repair costs for a machine are highly variable and good management may keep costs low [16]. Wear in agriculture working parts leads to an increase in fuel consumption and decreases the lifetime of these parts [17]. Table 2 shows the readability of agriculture machines for corn and soybean breakdown time [16].

Operation	Breakdown time (h/y)	Breakdown probability Per 40 ha.	Reliability per 40 ha.
Tillage	13.6	0.109	0.89
Planting corn	5.3	0.133	0.87
Planting soybeans	3.7	0.102	0.90
Row cultivation	5.6	0.045	0.96
Soybeans harvester	8.2	0.363	0.64
Corn harvester	12.3	0.323	0.68

Table 2.

Agricultural machinery reliability and breakdown probability [16].

1.1.2 Corrosion sources in agricultural machinery

Many studies stated that crop protection machine corrosion is caused by the effect of chemical pesticides and fertilizers used in farming. The metal elements of crop protection machines are exposed to the corrosive effects of pesticides. In addition, this corrosive effect is due to the direct connection among steel, brass, copper, and aluminum with pesticides [18, 19, 20, 21]. The sprayer content, especially the pump exposed to wear and corrosion, is due to corrosion and abrasive material used in crop production [22].

Moreover, there are studies indicating that when water is mixed with a pesticide in many stations from manufacturing, packaging, transportation, and usage increases the corrosion of metal surfaces of sprayers and it is a component, and due to that maintenance cost of machines is increasing [18, 21].

The key factors of fatigue and corrosion-fatigue failure of crop protection machines used in agricultural production determine the state of working surfaces, load parameters, environments aggressiveness degrees in consideration of the different kinds of fertilizer, and weather conditions. On examining the technical state of agricultural machinery after 3 years of operation, it is observed that corrosion contributes to approximately 80% of all mechanical failures of assembly units [6]. Many commercial chemicals are used in farming, including fertilizers, and chemicals for pests, disease, and weed control [23]. Corrosion is often more serious than the simple loss of a mass of metal. Corrosion may result in the reduction of metal thickness, leading to loss of mechanical strength and structural failure or breakdown (and structural failure or breakdown) [24].

Some fertilizers are more corrosive than others, especially if they decompose or react to produce aggressive substances such as ammonia or hydrogen sulfide; if chloride ions are present (including potassium or ammonium chloride), or if acidic conditions prevail. For example, dihydrogen ammonium phosphate or ammonium nitrate can lead to increased corrosion [18].

The most corrosive-active mineral fertilizers are nitrophosphate and ammonium sulfates, less aggressive is ammonia water, and humidity is a catalyst for corrosion processes. The relative ratios of the essential plant nutrients can influence the corrosiveness of compound liquid fertilizers, there being some evidence that the greatest effects occur with fertilizer solutions containing about 15% nitrogen, especially when half the free nitrogen is derived from urea and half from ammonium nitrate. Some typical reactions for liquid fertilizers are given in Table 3 [25].

Liquid fertilizers	Chemicals	Reactions with steel
Nitrogenous solutions	Ammonium nitrate, urea	Slow reaction with steel can be more rapid at weds and bolt holes, etc.
Phosphate solutions	Ammonium phosphate	Tends to be less reactive, forms a protective phosphate coat, which can protect the metal from subsequent attack by nitrogenous solutions unless acid conditions prevail.

Table 3.

Corrosive reactions of liquid fertilizers.

Farm wastes and slurries are known to be considerably corrosive. Also, chemicals most significantly damaging to farming structures and machinery are acid preservatives, additives, some fertilizers, and manures/slurries. As regards acid-cleaning chemicals, these can be used along with eco-friendly and bio-degradable [26].

Silo has a consistency akin to chipboard; therefore, equipment used for conveying and unloading silage can be subjected to corrosive wear. Abrasion and acid attack are also particularly destructive to concrete as acids are known to react with lime, which causes the concrete to become friable. Thus, this encourages the concrete to crack and eventually spall further, exposing the internal structure to inclement weather. Plastics, chlorinated rubber, and epoxy-based coatings are resistant to acid attacks and will provide alternatives as floor coverings over concrete in agricultural environments [27].

1.2 Solutions for reducing wear in agricultural machinery

There are many ways to reduce corrosion and increase the lifetime of the machine, such as the selection of the material, adapting to environmental conditions and surface treatment. Most of the agricultural machinery working parts need surface engineering (coating process) that resists wearing conditions and corrosion conditions during all their applications. Surface engineering includes thermal spraying, hard facing, heat treatment, electroless, and electrodeposition coatings [21, 28, 29, 30].

1.2.1 Using new materials

New materials against corrosion are important to improving the agricultural machinery sector [18]. Ryabova et al. [28] mentioned that high-strength new carbon steels had been used for soil processing agricultural machines. This steel has a yield strength of 1200, 1500, and 1700 MPa with different carbon content of 0.30–0.45%, economically alloyed with manganese, nickel, chromium, copper, and molybdenum (in total from ~2 to ~4%) in combination with a set of microalloying strong carbide-forming elements (titanium, niobium, vanadium) and boron.

1.2.2 Surface coating

In general, the coating of the material has an extra cost, but it is considered to be more functional, in long-term applications, because it supplies large savings in the maintenance cost. Surface coating is a branch of surface engineering science and it is one effective solution for tribological problems. Moreover, surface coating methods are applicable to decrease the friction coefficient, change the surface roughness, increase the surface hardness, induce residual compressive stresses, and reduce corrosion effect. So, they extend the lifetime and improve the corrosion and wear resistance. The coating methods can be categorized into several types as the gaseous state, solution state, and molten state of deposition techniques [31].

The electrochemical deposition technique is attractive due to the low energy consumption for depositing a coating on the different substrates. This technique has many advantages, such as low cost, ease of operation, versatility, and high yield. Important properties for electrodeposits include wear resistance, hardness, ductility, coating layer adhesion to substrate, and corrosion resistance. All these properties and characteristics can be affected by many of variables such as temperature, species concentration, electrolyte pH, current density, electrolyte flow conditions, and the use of electrolyte additives [32]. There are many studies about increasing abrasion wear resistance and corrosion resistance for agricultural machinery working parts by using nickel and hard chromium electroplating [33, 34, 35].

Electroplating mechanics is an electrochemical reaction during which metal oxidation occurs in electrolyte and transfers to metal ions after that metal ions are reduced on an electrically conductive substrate. It consists of oxidation-reduction reactions. Oxidation reaction and reduction reaction occur at the anode and at the cathode respectively [36]. There are many metals coating materials, such as silver, nickel, copper, tin, chromium, and lead on substrate, whereas the coatings of zinc, aluminum, and cadmium belong to the latter group. The metal layer must have pores by increasing the coating thickness [37].

Electroplating of nickel occurred from electrolytes containing nickel salts (sulfate and chloride) to cause dissolution of Ni²⁺ ions in the anode to be deposited at the cathode. At anode, nickel is the main metal rod where oxidation reaction happened, while cathode is a coating substrate needed to produce and reduction reaction happened [38, 39].

There are many methods used to carry out direct current (DC), alternating current (AC), and periodic current reversal (PCR) as shown in (Figure 17). DC method is used continuously for electrical current and DC method is economical and simple technology. In AC, an electrodeposition negatively charged layer is formed by currents in a periodic manner and reaches zero. There are two main stages pulsed on time and pulse of time. In pulse-off time period, it is permissible transferring the ions toward the cathode surface. The PCR electrodeposition process is used for the reduction of ions until arriving at zero by a change in polarity another effect of the PCR method is the lowest internal stresses in the deposit [40, 41].

Composite coating is become a trend in surface coating due to improving mechanical properties, abrasion resistant, corrosion resistance, reducing friction between moving parts, malleability, and increasing surface hardness. In addition, recent years were new trends in using nanoparticles as the incorporation particles into metal coating [42, 43, 44].

There are many types of electrodepositing baths commonly used for electrodeposition of nickel as Watt’s bath, chloride baths, citrate bath, and sulfamate bath. Nickel electrodeposition from a Watt’s bath has been used in many functional applications to modify or improve the corrosion resistance and increase wear resistance to increase the lifetime of service parts and reduce worm parts [45]. The physical and mechanical properties of nickel deposited from a Watt’s bath are affected by the electrodeposition parameters, such as deposition time, current density, pH, cathode material, electrolyte agitation, and electrolyte temperature, among others [46]. Nickel as a metal base for composite coating is appropriate for wear resistance in industrial systems, gear systems, measuring tools, and abrasive tools [47, 48].

Nanocomposite coating technique is a new surface coating deposition process with physical and mechanical unique properties due to mixing two or more materials in the nanoscale [49]. Nanoparticle incorporation in the metal matrix can increase hardness, increase corrosion resistance, modify growth coating to deposit nanoparticles, and shift the reduction system of metal ions [32].

Table 4 shows a summary of the effect of Ni composite and Ni nanocomposite on improving the chemical and mechanical properties of steel. From this table, an improvement in mechanical and chemical properties of surfaces is evident due to adding micro- and nano-element to the nickel coating.

substrate	Corr. rate	Wear rate	Hardness
Uncoated mild steel	0.181 mm/y [27]	0.018 mm^3/N-m [50]	180 HV [27]
Uncoated low-carbon steel	0.310 mm/y [51]	0.038 mm^3/N-m [52]	166 HV [51]
Steel coated with pure Ni	0.049 mm/y; [27]; 0.110*10^−3mpy [53]	13.5 × 10^−4 mm^3/N-m; [47]; 1.2 mg/h; [54]; 5.596 × 10^−5 mm^3/m; [55]	243 HV; [27]; 245 HV; [56]; 280 HV; [54]
	Composite coating
Steel coated with Ni-Cu	0.170 mm/y [57]	15.18*10^−4 mm^3/N-m [56]	331 HV [57]
Steel coated with Ni-Cr	0.038 mm/y [51]	0.9 mg/h [54]	385 HV [54]
Steel coated with Ni-Zn	0.144 mm/y [58]	6.83*10^−3 mm^3/N-m [59]	253 HV [60]
Steel coated with Ni-W	—	—	506 HV [61]
	Nanocomposite coating
Steel coated with Ni-W/Cr2O3	0.00670 mm/y [62]	—	498 HV [62]
Steel coated with Ni-GNS	0.0180 mm/y [27]	—	250 HV [27]
steel coated with Ni-GNS-TiO2	0.0004 mm/y [27]	—	478 HV [27]
Steel coated with Ni-TiO2	0.051*10^−3 mpy [53]	2.99 × 10^−5 mm^3/m [55]	480 HV [53]
Steel coated with Ni-SiO2	0.03784 mm/y [63]	—	—
Steel coated with Ni-W-SiO2	—	—	823 HV [64]
Steel coated with Ni-Co-SiO2	4.14*10^−6 mm/y [65]	—	502 HV [65]
Steel coated with Ni-Al2O3	—	18.7 mg/min [66] 2.44*10^−4 mm^3/N-m [50]	905.4 HV [66]; 641 HV; [67]
Steel coated with Ni-Cu/ Al2O3	—	—	570 HV; [56]
Steel coated with Ni/SiC	—	5.29*10^−4 mm^3/N-m [68]	495 HV [68]
Steel coated with Ni-SiC/Al2O3	—	4.95*10^−4 mm^3/N-m [68]	525 HV [68]
Steel coated with Ni-Cr	—	0.4 mg/h [54]	550 HV [54]

Table 4.

Effect Ni-composite and nanocomposite coating on improving the steel surface.

1.2.3 Inhibitor

Inhibitors are chemicals used to protect metallic surfaces. Inhibitors often work by adsorbing themselves on the metallic surface, protecting the metallic surface by forming a film. Inhibitors are normally distributed from a solution or dispersion. Some are included in a protective coating formulation. Inhibitors slow corrosion processes by increasing the anodic or cathodic polarization behavior (Tafel slopes), reducing the movement or diffusion of ions to the metallic surface, and increasing the electrical resistance of the metallic surface [69].

Monticelli mentioned that the standardized definition of a corrosion inhibitor is a “chemical substance that, when presented in the corrosion system at a suitable concentration, decreases the corrosion rate, without significantly changing the concentration of any corrosive agent” [70]. Abbout [71] proposed several characteristics that need to be possessed by an effective corrosion inhibitor, namely, stability at a certain temperature, low cost, and, more importantly, adherence to environmental laws and standards [71].

The corrosion inhibitors can be chemicals either synthetic or natural and could be classified by the chemical nature as organic or inorganic, the mechanism of action as anodic, cathodic, or an anodic-cathodic mix, and by adsorption action, or as oxidants or not oxidants [70].

The cathodic corrosion inhibitors prevent the occurrence of the cathodic reaction of the metal. These inhibitors have metal ions able to produce a cathodic reaction due to alkalinity, thus producing insoluble compounds that precipitate selectively on cathodic sites. Deposit over the metal a compact and adherent film, which restricting the diffusion of corrosion action in these areas. Thus, increasing the impedance of the surface and the diffusion restriction of the reducible species, that is, the oxygen diffusion and electrons conductive in these areas. These inhibitors cause high cathodic inhibition [72].

The label “green,” or sometimes “eco-friendly,” is commonly added to the noun inhibitor if the molecule, in addition to meeting the previous definition of inhibitor, also has biocompatibility in nature. Part of this class of inhibitors is complex matrices like plant extracts due to their biological origin and, by extension, their single components, such as flavonoids, alkaloids, polyphenols, and glycosides [73].

The relative simplicity of many extraction procedures, combined with the plenty of vegetable sources available even at very low prices, made the exploitation of plant extracts a new “trend” in corrosion science. This “green turn” must surely receive praise, but it is to be worth noting also the other side of the medal. A critical revision of the open literature concerning green corrosion inhibitors brings up a constructive critique [74]. Table 5 summarizes different types of green inhibitors.

Plant name	Additive	Results	Authors
Apricot juice	Phosphoric acid	a corrosion inhibitor of mild steel with maximum inhibition efficiency of 75% at 30°C	[75]
Amber	Succinic acid	Succinic acid was used as an inhibitor of the corrosion process at a temperature of 25°C at pH values ranging between (8 and 2), where they studied the effect of the concentration of the inhibitor on iron corrosion and the results were good, as the highest percentage of inhibition was about 97% at a pH value of 8	[76]
The garlic	The garlic extract	GAE was shown to inhibit corrosion in both metals in the presence and absence of bacteria; inhibition efficiencies were about 81 ± 3% and 75 ± 3% for the abiotic system while 72 ± 3% and 69 ± 3% in the presence of mixed bacterial consortia for CS and SS, respectively.	[77]
Ocimum basilicums	The iodide	Weight loss tests were utilized to assess the corrosion inhibition performance of Al alloy AA8011 in an alkaline environment using eco-friendly corrosion inhibitors.a decrease in the corrosion rate of the Al alloy from 0.407 mmpy to 0.106 mmpy in 0.25 M KOH was noted after a span of 5 h supporting the excellent inhibition performance of the extract.	[78]

Table 5.

The different types of green inhibitors.

2. Conclusions

Agricultural machinery is considered one of the most important lines of defense for achieving global food sufficiency. Therefore, the sustainability of these machines is one of the important issues. One of the most important factors that lead to reducing the life span of agricultural machinery is corrosion. There are many scientific methods used to reduce the wear of agricultural machinery, such as modern coatings, corrosion inhibitors, and the selection of modern materials.