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Guidelines for Metal Selection 2016-12-29T09:16:42+00:00

Guidelines for Metal Selection

Metal and metallic composition gaskets are used where high temperatures and corrosive media are involved. The metal used shall be dictated by its degree of heat resistance and its corrosive resistance and its corrosive resistance to the media sealed. The following metals are readily available for gasketing. No attempt is made to elaborate on each, only to generalize their usage.

BRASS
An alloy of copper and zinc with addition of other elements. Brass falls into three basic categories:

PLAIN BRASS
Where copper content is above 50% of total composition with balance being zinc. Muntz metal, red brass, and commercial bronze fall into this category.

FREECUTTING BRASS
An additional element is added to copper and zinc, normally lead. Leaded brass and commercial bronze fall into this category.

MISCELLANEOUS BRASS
The addition of added elements to copper and zinc, other than lead. Naval brass and Admiralty fall in this category.

Generally, copper alloys are used successfully with non-oxidizing acids such as acetic, sulfuric acid, diluted hydrochloric and phosphoric acid. Has resistance to alkaline and neutral salt solutions. Acids such as nitric, sulfurous and concentrated sulfuric, and acids carrying oxidizing agents normally attack copper alloys. Brass has poor resistance to sulfur.

ALUMINUM
Lightweight metal, with high strength capability, which is covered with a thin oxide film that is highly resistant and protective. Aluminum alloys are used in the petroleum, rubber processing, chemical, aeronautical, pharmaceutical, and plastic industries, and steam power plants. It has excellent corrosion resistance to organic acid solutions with the exception of nitric acid. Resists the action of most alcohols at low temperatures. Well suited for handling steam or steam condensate.

COPPER
A metal having electrical conductivity, corrosion resistance, malleability and strength, forms readily and work hardens slowly. Copper is highly resistant to effects of atmosphere, naturally occurring fresh and salty waters, alkaline solutions (except those containing ammonia), and many organic chemicals. Copper is used successfully in acetic acid and related chemicals, neutral salts such as nitrates and sulfates, and a wide range of organic compounds. Oxidizing salts corrode copper rapidly and should not be used.

TYPE 304 STAINLESS STEEL
In the annealed condition, withstands rusting, is immune to most organic chemicals and dyestuffs, and a wide variety of inorganic chemicals. It resists nitric acid well, halogen acids poorly, and sulfur acids moderately.

TYPE 316 STAINLESS STEEL
It is a molybdenum-bearing austenitic steel with increased percentage of nickel. Offers higher corrosion resistance than Type 304. Resist sulfurous acid compounds.

TYPE 309 STAINLESS STEEL
12% nickel with 22% chromium. The higher alloy content of this grade improves corrosion resistance and increases oxidation resistance to 2000°F. Creep strength is slightly better than Type 304, but less than Type 316.

TYPE 321 STAINLESS STEEL
A stabilized alloy similar to Type 304 with titanium added. Widely used in high temperature corrosive service.

TYPE 347 STAINLESS STEEL
A stabilized alloy similar to Type 304 with columbium and tantalum. Used high temperature corrosive service.

TYPE 410 STAINLESS STEEL
A martenistic type. A heat-treatable 12% chromium steel combining good general corrosion resistance with high strength.

HASTELLOY “B”
A corrosion resistant alloy. Effectively resists corrosion of hydrochloric acid under most conditions as well as phosphoric acid, other halogen acids, and reducing conditions.

HASTELLOY “C-276”
Exceptional resistance to severe oxidizing conditions encountered with nitric acid, free chlorine, and strong aqueous and acid solutions.

STEEL
Used normally in soft annealed temper, exceptional formability and deep drawing. Widely used for handling of sulfuric acid in heavy concentrations. Unsatisfactory when media is hydrochloric acid in any concentration.

MONEL
A nickel-copper alloy. For general applications requiring corrosion resistance in addition to toughness and high strength. Has found use in heat exchangers, petroleum process vessels, boiler feed water heater, valves and pumps, and chemical processing equipment.

NICKEL
Has high degree of corrosion resistance to natural and distilled water. Resists neutral and alkaline salt solution, as well as alkalis such as caustic soda. It does not possess useful resistance to corrosion of oxidizing acids such as nitric acid. Strong, hot sulfurous acids are very corrosive to nickel. It is particularly useful in the food, synthetic fiber, and chemical industries.

INCONEL 600
A nickel-chromium alloy. Withstands high temperatures. Has exceptional resistance to corrosion by halogen gases and compounds.