Corrosion-Resistant Valves

In general, valve bodies and boimets should be manufactured in a material similar to that used for the piping or vessel to which they are attached. Valve trims should be manufactured in a more resistant material to prevent erosion/ corrosion the choice of materials being dependent upon the process conditions. 

Where electroless nickel plating of valve internals is approved by the company (e.g. for ball valves or parallel shde gate valves), the following reqnirements should be met  

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NOTE Outline drawings for flanged valves shown VS-in raised face machined onto flange, as for 400-lb cast-steel valves 150- and 300-lb cast-steel valves and 2.50-lb cast-iron valves have i/ifi-in raised faces 125-lb cast-iron and 150-lb corrosion-resistant valves covered by MSS-SP-42 have no raised faces. 

AH columns, distributors, and ancHlary hardware such as piping, valves, and pumps must be constmcted of corrosion-resistant materials, or coated with an appropriate substance. AH streams that contact the hardware during each step of the cycHc operation need to be considered in this selection. 

Chemically Functional. Refractory coatings are used for corrosion-resistant high temperature service in gas turbine and diesel engines, components such as cmcibles, thermocouple protection tubing, valve parts, etc. 

Other martensitic grades are Types 501 and 502. The former has >0.10% and the latter <0.10% carbon. Both contain 4—6% chromium. These grades are also air-hardened, but do not have the corrosion resistance of the 12% chromium grades. Types 501 and 502 have wide appHcation in the petroleum industry for hot lines, bubble towers, valves, and plates. 

Standard stainless steels have significantly greater corrosion resistance to oleum than carbon steel, but higher price may make these materials less economical, except for special services such as valves, Hquid distributors, oleum boilers, etc. 

Uses. Uses for copper—siUcon alloys are siUcon bronze, UNS C 87200, as bearings, pumps, valve parts, marine fittings, and corrosion-resistant castings siUcon brass UNS C 87400 as bearings, gears, impellers, valve stems, and clamps and siUcon brass UNS C 87500 as small propellers, valve stems, gears, and bearings. 

Uses. Copper—nickel—iron alloys, UNS C 96200 (90 10 copper nickel) and UNS C 96400 (70 30 copper nickel), are used in corrosion-resistant marine (seawater) appHcations. UNS C 96400 is used for corrosion-resistant marine elbows, flanges, valves, and pumps. Leaded nickel—brass, UNS C 97300 (12% nickel-silver), is used for hardware fittings, valves, and statuary and ornamental castings. 

Recently in some types of refuelling stations, corrosion-resistant materials have been used between the filter-water separator and the outlet pipeline and valves, usually stainless steel, rarely aluminum. If these are buried, they must have good insulating coating and be electrically separated from other tank installations by insulating couplings. 

The filter elements should be replaceable and should be corrosion resistant. The filter should not contain any type of internal relief valve that would permit the bypassing of the dirty oil. 

Industrial equipment is a continuing area of development for plastics. Pipes, pumps, valves and sight glasses, made from such materials as PVC, PTFE and poly-4-methylpent-l-ene, have become well established on account of their corrosion resistance. The nylons are used for such diverse applications as mine conveyor belts and main drive gears for knitting machines and paper-making equipment. These and other materials are widely used where such features as toughness, abrasion resistance, corrosion resistance, non-stick properties, electrical insulation capability and transparency are of importance. 

Applications include high-performance insulation for wire and cables (particularly heater cables), and corrosion-resistant linings for pumps, valves, pipes and other chemical equipment. Its availability in the form of film and tubing has led to its demand for both corrosion protection and antistick applications. 

Halstrick, V. and Kirchner, W. 1996. Corrosion-Resistant Flame Arresters and Valves. Protego Technical Paper ha-sd 0660E780. DOC/8. Braunschweiger Flammenfilter GmbH, Braunschweig, Germany. 

For these special situations properly designed rupture disks using corrosion-resistant materials can be installed both before the valve inlet as well as on the valve discharge. For these cases, refer to both the valve manufacturer and the rupture disk manufacturers. See later discussion of code requirements for this condition. 

They must be readily accessible for cleaning, which should be carried out as frequently as necessary to ensure that pressure drop across the filter does not affect normal oil flow rates. The filtering medium should be of corrosion-resistant material such as Monel metal, phosphor-bronze or stainless steel. All first-stage filters should be provided with isolating valves. 

The corrosive and mechanical effects of flow are observed in pipes, especially at bends and downstream of flow disturbances, tube and shell heat exchangers, valves and pumps. More corrosion and/or harder materials are used in such areas. Austenitic stainless steels work harden and hence are superior in flowing conditions to ferritic stainless steels of otherwise similar corrosion resistance. Hard... 

Nickel is usually alloyed with elements including copper, chromium, molybdenum and then for strengthening and to improve corrosion resistance for specific applications. Nickel-copper alloys (and copper-nickel alloys see Section 53.5.4) are widely used for handling water. Pumps and valve bodies for fresh water, seawater and mildly acidic alkaline conditions are made from cast Ni-30% Cu type alloys. The wrought material is used for shafts and stems. In seawater contaminated with sulfide, these alloys are subject to pitting and corrosion fatigue. Ammonia contamination creates corrosion problems as for commercially pure nickel. 

The austenitic irons also show good corrosion resistance in caustic alkalis containing sulphides and mercaptans and have therefore proved useful materials for the construction of pumps, valves and piping in caustic soda regenerators in oil refineries. 

AUSIOIA Type 1 Least expensive austenitic iron good corrosion resistance particularly in acidic media Pumps, valves, furnace components... 

AUS104 AUS204 - Good resistance to high temperature oxidation good corrosion resistance in sulphuric acid Pumps and valves... 

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