Rubber lining corrosion

Dry chlorine has a great affinity for absorbing moisture, and wet chlorine is extremely corrosive, attacking most common materials except HasteUoy C, titanium, and tantalum. These metals are protected from attack by the acids formed by chlorine hydrolysis because of surface oxide films on the metal. Tantalum is the preferred constmction material for service with wet and dry chlorine. Wet chlorine gas is handled under pressure using fiberglass-reinforced plastics. Rubber-lined steel is suitable for wet chlorine gas handling up to 100°C. At low pressures and low temperatures PVC, chlorinated PVC, and reinforced polyester resins are also used. Polytetrafluoroethylene (PTFE), poly(vinyhdene fluoride) (PVDE), and... 

As every operator of a mercury cellroom knows, corrosion of rubber-lined parts of the cell is a general occurrence. The softer the rubber, the higher the speed of corrosion. 

With reaction conditions of 200-225°F, 150—225 psi, and a palladium chloride-cupric chloride catalyst, MEK yields are 80-90%. The operating costs of the Wacker process for MEK (and acetone and several other petrochemicals as well) are relatively low. But the plant Is made of more expensive materials. Because of the corrosive nature of the catalyst solution, critical vessels, and the piping are titanium-based.(chats expensive ), and the reactor is rubber-lined, acid-resistant brick. ... 

The principal benefits of rubber lining are its excellent resistance to corrosive and abrasive chemicals and materials, e.g., acids, alkalies, salt water, slurries, sand, shot blast media, crushed ores etc. In addition to this, rubber linings provide other benefits including noise and vibration reduction, electrical and thermal insulation and product protection. 

Whilst carbon and stainless steels are commonly used materials of construction, increasing use is being made of non-metallic and rubber lined equipment. The selection of the material of construction should take into account the cases of the worst process conditions that may occur under foreseeable conditions and should be applied to all components including valves, pipe fittings, instruments and gauges. Both composition (e.g., chlorides, moisture) and temperature deviations can have a significant direct effect on the rate of corrosion. The operator should demonstrate that procedures are in place to ensure that potential deviations in process conditions such as fluid temperature, pressure and composition are identified and assessed in relation to the selection of materials of construction for piping systems. 

This acid is very corrosive towards most of the common metals and alloys. The corrosivity is increased where aeration or contamination by oxidising agents is present. Copper is particularly prone to this problem. Also many failures occur due to the presence of minor impurities such as ferric chloride. Rubber-lined steel is widely used for pipelines and large or small vessels. The rubber compound should be free from copper bearing antioxidants or accelerators. 

Materials of construction for ammonia are dependent on the operating temperature. Whilst mild steel may be used at ambient temperature, special costly steels are required at low temperatures to avoid embrittlement. Impurities in liquid ammonia such as air or carbon dioxide can cause stress corrosion cracking of mild steel. Ammonia is highly corrosive towards copper and zinc. Rubber lined steel construction is suitable for service at ambient temperature. 

Marine Industry Corrosion resistant linings for fume scrubbers and cooling pipelines. Wear resistant linings for dredging pipelines. Ebonite or hard rubber for corrosion resistance. Soft natural rubber for wear resistance. 

The thickness of lining depends on the severity of corrosion or erosion. The diffusion of liquids is inversely proportional to the square of the thickness of the lining at a given temperature. That is to say, a 6 mm thickness is four times more resistant than a lining of 3 mm thickness. The speed of diffusion in the temperature range 30-80 deg C is proportional to the temperature increase. The fabricators of vessels are to be informed in advance that the vessel is meant for lining and should be asked to follow the standard procedure for fabrication of equipment meant for rubber lining. 

Design and fabrication of tanks, vessels, piping and other equipment which are required to be protected with rubber lining against corrosion need special consideration in chemical plant construction. Certain features are to be incorporated in the design, and precautionary methods should be taken while fabricating the mild steel equipment to be suitable for rubber lining application. These are discussed below. 

The solids are thrown outwards against the wall of the vessel and then move away from the gas inlet and are collected in the conical base of the equipment. This separation process is very effective unless the gas contains a large proportion of solid particles less than 10 p in diameter and is equally effective when used with dust or mist-laden gases. The cyclone separators are obviously rubber lined to withstand wear at the velocity of gas and corrosion and are the most commonly used general purpose separator in the chemical process industry. 

The chemical reaction of rubber lining with the corrosive chemicals and acids is much deteriorating to it, resulting in progressive damage of the lining, unless the reaction is not allowed to continue... 

Rubber sheets are the most important materials for the construction and fabrication of much chemical plant equipment such as storage tanks, reactor vessels, pipelines, seals, hoses and rubber lined mild steel equipment of different sizes and shapes, inflatables, etc., and almost all equipment subjected to different corrosive environments. The rubber sheets can be either plain or fabrics coated with rubber. The fabrics used for coating are nylon, rayon, cotton or various other synthetics. Rubberized fabric cords are also used as reinforcing members in various products. 

The materials handled in the bins were 20% solids by weight, flow of 2.9 tons of water per hour and 47 gallons/minute of pulp. The size of the material was 100 to plus 325 BSS mesh. Maximum acid concentration was 20% hydrochloric acid. The temperature in the system was 60°C. A 6 mm thick natural rubber lining of shore hardness 50°A was used to protect the equipment against the abrasive environment as well as the corrosion effects of hydrochloric acid. 

Phosphoric acid is corrosive to most construction materials and rubber-lined steel or food-grade stainless steel holding vessels are generally recommended. 

Sometimes the vessels arc lined with a corrosion resisting material (lead, tiles, cement, tar, asphalt, rubber or synthetic resins). Lead is used to line both wooden and steel vessels enameled steel vessels are sometimes used in small plants if electrolysis is to proceed at a higher temperature. Acid proof tiles used for the lining of steel yessels are mounted on a cement basis. A coating of tar or asphalt can sometimes be used to line a wooden container instead of the more expensive lead. Steel electrolyzers are frequently used with a natural or synthetic rubber lining. 

If the environment slowly attacks either the substrate or the membrane, the interposition of a brick lining between the contained liquid and the substrate or membrane will reduce to a tiny trickle the amount of chemical that reaches the membrane or substrate. Corrosion products, if any, are trapped behind the brick and cannot be washed away to uncover further material to be corroded, so that the corrosion slows down and may eventually stop. Example In a dished bottom, cylindrical steel tank containing a mixture of acid and oil, the steel was lined originally with sheet natural rubber. The rubber lining swells as the oil enters it, but the brickwork holds it in place until the rubber has swollen into all the pores of the brickwork and blocked them preventing any more of the contained liquid from passing behind the brick. 

Typically, the entire contents of a calcium hypochlorite container are emptied into a mixing tank where they are readily and completely dissolved in water. The resulting corrosive solution is stored in and fed from a stock solution vessel constructed of corrosion-resistant materials such as plastic, ceramic, glass, or rubber-lined steel. Solutions of 1% or 2% available chlorine can be delivered by a diaphragm-type, chemical feed pump or metering pump. 

Severe corrosion conditions which exist throughout this process have led to the use of wood, lead-lined wood, polyester-fiberglass, and rubber-lined steel for construction of much of the equipment, with dense carbon or a nickel alloy being favored for heat exchangers. 

---