Use of 3CR12 in the Sugar Industry
3CR12 is a weldable, structural, corrosion resistant steel containing a nominal 12% Chromium. 3CR12 was originally developed as an alternative material of construction to materials such as mild steel, galvanised and alurninised steel, where the mechanical properties and corrosion resistance of these materials was unsuitable.
With an average life expectancy of 5 to 10 times that of mild steel and at considerably less cost than higher grades of stainless steel, 3CR12 is recognised as an extremely effective alternative to coated mild steel, resulting in minimum capital cost increases and significant maintenance cost savings.
3CR12 has been in use in the sugar industry, locally and world-wide, since 1980 and has become an accepted material in many applications ranging from the cane yard to the final product.
3CR12 exhibits excellent properties in wet sliding abrasion applications by resisting corrosive attack, therefore improving flow and reliability. This allows widespread use of 3CR12 in cane sugar and beet handling applications, where abrasion is aggravated by the moisture and solids present in the cane and beet being processed.
The Benefits Of 3CR12 Corrosion Resistance
All metals react with oxygen and water in he air to form a surface layer of oxide. That formed on carbon steel is soft, friable, hydrated iron oxide rust. The process of rust degeneration is greatly accelerated by surface abrasion or scouring.
3CR12 with a nominal 12% Chromium content, has an inert tough surface layer of iron-chromium oxide. This passive layer is invisible to the naked eye, allowing the natural brightness of the metal to be seen. If scratched, the film has the ability to reform instantaneously, thus maintaining protection.
With mild steel, abrasion removes the corroded layer and exposes fresh reactive surfaces for further corrosion to take place.
3CR12’s excellent wet sliding abrasion properties are derived from its superior corrosion resistance and slideability. Under dry conditions, 3CR12 offers only marginal improvement over mild steel, but under wet or damp conditions (eg. over 4% moisture), the corrosion vector is underestimated. Dry conditions are seldom encountered in the cane sugar and beet sugar industry.
When the cost per unit loss by corrosion abrasion is taken into account, 3CR12 is superior to other grades tested. (See histogram right).
Cane Sugar Processing
The sugar industry is characterised by high maintenance costs due to the replacement and repair of equipment due to corrosion and corrosion abrasion.
Sugar cane is not washed prior to cutting and crushing in the mills and the presence of sand and stone contribute to the abrasive conditions that already exist.
3CR12 with its excellent wet sliding properties improves the flow of materials and has gained rapid acceptance in cane handling and bagasse applications. It has also gained acceptance in most other areas within the sugar mills due to its corrosion resistance and superior mechanical properties.
Examples of the many applications where 3CR12 has been used in the processing of sugar cane are listed below
MS Diffuser Internals Maidstone Sugar Mill have installed their second diffuser which was comissioned in the 1995 season. The diffuser is 70 metres long, 10 metres wide and capable of processing 300 tonnes of sugar cane per hour The roof, side wall internals, perforated floor sections and lifting screws have been fabricated from 3CR12.
Felixton Ash Settler
3CR12 is proving its worth in corrosion abrasion applications as liners on cane carriers and deck plates on intercarriers and ash disposal carriers. The photograph on the left is of the Felixton sugar mill ash seffler deck plates which were installed in 1992 and are still in excellent condition. The carrier disposes wet ash originating from bagasse burnt in the boilers.
Transvaal Sugar’s (T.S.B.) new Komati mill in Komatipoort started production in March 1994, processing 225 tonnes of cane per hour which has doubled over the past five years.
3CR12 is being used in areas where corrosion and corrosion abrasion present high maintenance demands.
The Komati mill has installed 3CR12 in its conveyor systems, cane carrying, diffuser feed slat and sample system conveyors. In the juice extraction area where the acidic nature of the product can rapidly degrade mild steels, 3CR12 has been used for the diffuser side walls, roof and some juice piping. Chutes and intercarriers in this area have also been fabricated in 3CR12.
Downstream production machinery fabricated using 3CR12 includes the clarifier launders and root mud mixers, filter frame, agitator, trough and hood filtration piping. The evaporator tubes and fourth effect condenser, pan tubes and condensation pipes have also been fabricated from 3CR12. Further into the mill, 3CR12 has also been used to build the centrifugal monitor casings, sugar screw conveyors and sugar scales.
In total, over 450 tonnes of 3CR12 has been used in the Komati mill, demonstrating the versatility of the 3CR12 applications throughout the factory.
|0.03%||1.5%||1.5%||1%||0.03%||0.03%||11% to 12%||0.6%|
Mechanical Properties at Room Temperature
|Ultimate Tensile Strength||460||MPa||min|
|Proof Strength (0.2% offset)||280||MPa||min|
|Elongation (in 50mm)||t < 4.5 mm||18||%||min|
|t > 4.5 mm||20||%||min|
|Hardness||t < 12 mm||220||BHN||max|
|Charpy Impact (20°C)||35||J/cm3||min|
|Modulus of Elasticity (tension)||200||GPa|
|Specific Heat Capacity||460||J/kgK|
|Thermal Conductivity||at 100°C||23||W/mK|
|Electrical Resistivity||at 25°C||660|
|Coefficient of thermal expansion||0-100°C||10.8||μ/m°C|
|German Werkstoff Equivalent||1.4003|
|American Equivalent||ASTM A240 410S|
3CR12, a registered trade mark of Stainless steel product, is a weldable chromium containing utility stainless steel, with a fine grained duplex ferritic-martensitic microstructure.
Stainless steel 3CR12 is a proprietary modification of Grade 409 chromium stainless steel. It has been developed as a readily fabricated, low cost grade, exhibiting good resistance to wet abrasion and mildly corrosive environments. National specifications cover this grade by designations 1.4003 and UNS S40977 / S41003.
Proprietary 3CR12 conforms to EN 10088.2 grade 1.4003, ASTM A240/ A240M grades UNS S40977 and S41003 and ASME SA240 grades UNS S40977 and S41003. 1.4003 is also included in EN 10028.7 covering stainless steels for pressure purposes.
Like other chromium stainless steel, 3CR12 has useful strength at temperature about 600oC. This ele vated temperature strength is significantly higher than that of plain-carbon steels. Hot working can be carried out at 700ºC – 800ºC without significantly affecting subsequent mechanical properties. Above 850ºC, 3CR12 behaves superplastically due to the fine grained duplex microstructure.
|0.03 Max||0.1 Max||0.15 Max||0.40 Max||0.03 Max||1.5 Max||10.5 – 13.0||0.06 Max||0.03 max|
|0,2% Proof Stress||< 3mm
|280 MPa (Min)
300 MPa (Min)
|Tensile Strength||460 MPa|
|Elongation in 50mm G.L||≤ 4.5mm
|Charpy Impact V 20ºC|
Possible Alternative Grades
Possible alternative grades to grade 3CR12 stainless steels are given in table.
|Why it might be chosen instead of 3CR12|
|Better corrosion resistance and fabrication properties are required.|
|Better corrosion resistance and appearance is required. Weldability not needed.|
|A lower cost is required, and the reduced corrosion resistance and
fabrication characteristics of galvanised steel are acceptable.
|A lower cost is required, and the reduced corrosion resistance and
fabrication characteristics of weathering steel are acceptable.
3CR12 is effective in many applications where carbon steel, galvanised, aluminised or painted steel or aluminium give unsatisfactory life. It is not attacked by strong alkalies, and often gives adequate resistance in acidic conditions.
3CR12 strongly resists chloride stress corrosion cracking, but is less resistant than 304 to pitting and crevice corrosion in chloride environments. 3CR12 is likely to resist water with chloride contents of up to 150 to 200 mg/L at ambient temperatures. The presence of sulphate or nitrate ions will reduce the corrosivity of chlorides. Light surface rust can form in many atmospheres, making the material unsuitable for decorative applications.
In air 3CR12 offers scaling resistance to 600°C continuous or 750°C intermittent, but if under stress the temperature should be limited to 450°C continuous or 600°C intermittent. 3CR12 suffers negligible embrittlement after extended exposure at temperatures of 450-550°C; it can be used safely at these temperatures without loss of room temperature impact resistance.
Annealing – heat to 700-750°C, soak for 1½ hours per 25mm section. Air cool. The maximum temperature of 750°C should not be exceeded. Annealing should usually be followed by pickling and passivating.
This grade should not be hardened by heat treatment; quenching treatments may reduce the corrosion resistance and mechanical properties.
3CR12 can be readily welded using similar techniques to austenitic stainless steels. Low heat input processes are preferred – particularly GTAW (TIG) and GMAW (MIG). Filler wire pre-qualified by AS 1554.6 (3CR12 referred to as “4003”) is grade 309, but 309L, 309Mo, 316L and 308L have been successfully used. Argon plus 1-2% oxygen shielding gases are recommended. Discolouration of the weld should be removed by pickling, except possibly in wear applications; effective purging and use of backing gases is often a better option.
3CR12 has a machinability similar to that of grade 430, ie about 60% of that of mild steel. The work hardening rate is lower than that of austenitic stainless steels, so reducing the need for special machining techniques.
3CR12 is available in standard HRAP (Hot Rolled Annealed and Pickled) finish in plate, and 2B or 2D in coil. “Black” finish is also produced; this is hot rolled and with the high temperature scale left on the steel. The resulting dark oxidised surface has good low friction characteristics and a corrosion resistance that is useful for many wear applications, even although slightly less resistant than the “white” pickled finish.
3CR12 is a particularly recommended for use on moderately aggressive environments found in the construction, industrial, marine, mining and mineral
processing fields. It provides a cost effective solution to corrosion, oxidation and corrosion/abrasion problems in a wide range of environments. Typical examples include:
• Ore Cars
• Pipe & Tube for Slurry Handling
• Coal Chutes and Liners
• Storage Bins and Hoppers
• Locomotive Bodies
• Ash Handling
• Masonry Fixings
• Coal Wash Plant Structure
• Conveyor Decking
• Sand – Chutes Dredging
• Screw Conveyors
|More Detail »|
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