I/EC A
CORROSION
W O R K B O O K
F E A T U R E
by Arthur I. Heim, Research Engineer, Copper and Brass Research Assoc.
Corrosion Resistance of Copper and Copper Alloys Copper has good corrosion resistance to many chemicals, but there are certain applications where the conditions, under which contact is made, influence the degree of resistance
I N F E B R U A R Y 1957,
we
looked
at
the different types of corrosion to which copper and its alloys are susceptible. This month, some of the specific conditions and media which affect the corrosion resistance of copper are discussed. Temperatures at which corrosive mixtures are handled have an important effect upon the rate of attack, as do the concentrations. Most acids are less corrosive in dilute solutions than when concentrated, and when cold than when hot. Oxygen or oxidizing agents in a solution tend to accelerate the corrosion rate on copper and copper alloys.
T h e patina which forms is an effective corrosion inhibitor. Acids-Alkalies
Copper alloys are rapidly attacked by oxidizing acids such as nitric and chromic acids. Corrosive attack by other acids usually depends upon the presence of oxygen or some other oxidizing agent in the solution. Brasses which contain not more than 1 5 % of zinc can be used with many acids, but in general, high-zinc brasses should not be used with acids. Copper, red brass, phosphor bronze, copper-silicon alloys, alumi-
Temperature and Concentration Effects
Temperature Up to 100° F. 100 to 175° F. Over 175° F.
Eled brass-sodium hydroxide Concentration, % 20 40 60 S S S HR6 HR HR HR HR
" S, satisfactory. NR, not recommended.
80 S HR* HR
100
s HR HR
6
Atmospheres
Virtually all copper and copperbase alloys are highly resistant to the corrosive effects of atmospheres, whether industrial, marine, or rural. Some alloys will pass through brown and black tarnish stages prior to forming the familiar green patina. T h e principal constituent of the patina, which usually takes 8 to 10 years to form, is basic copper sulfate (brochantite) [ ( C u S 0 4 - 3 C u ( O H ) 2 ] . Copper, M u n t z metal, red brass tube, and architectural bronze extruded shapes all serve exceptionally well against atmospheric corrosion.
n u m bronze, and cupronickel are highly resistant to both hot and cold dilute sulfuric acid. H o t concentrated sulfuric acid m a y cause corrosive localized pitting. Interestingly enough, some intermediate concentrations of sulfuric acid are more corrosive to copper alloys t h a n the same acid in either concentrated or dilute solutions. M a n y of the copper and copper-base materials give reasonable resistance to both dilute and concentrated hydrochloric acid at room temperature. Corrosive attack is more rapid when the acid is hot a n d concentrated. Copper, red brass,
cupronickel, aluminum bronze, and copper-silicon alloys can be considered for handling hydrochloric acid. Organic acids are usually less corrosive than the mineral acids. Copper and many of its alloys can handle sodium and potassium hydroxide solutions of all concentrations at room temperature. Most of the materials are also resistant to hot dilute alkalies. Cupronickel, 3 0 % , is most resistant to corrosion by alkalies. O n the other hand, binary copper-zinc alloys containing more than 1 5 % zinc should not be used because of the possibility of dezincification. Although copper and copper alloys are not corroded by ammonia that is absolutely dry, they are r a p idly attacked by moist ammonia and ammonium hydroxide solutions. Corrosion is caused by the formation of complex soluble copper a m m o nium compounds. Ammonia in the presence of moisture and air may cause stress-corrosion cracking—often referred to as season cracking— of certain copper alloys. Of all the copper-base alloys, cupronickel, 3 0 % , is the most resistant to corrosion by moist a m m o n i a or a m m o nium hydroxide and should offer fair resistance to such corrosion at ordinary temperatures. Salt Solutions
Alkaline salts, including sodium carbonate, sodium phosphate, and sodium silicate, react with copper and copper alloys, but with somewhat less corrosive action than the hydroxides. Neutral salt solutions are extensively handled in copper alloy equipment. However, equipVOL. 49, NO. 8
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AUGUST 1957
63 A
A Workbook Feature
Acetic acid 2 2 4 2 3 2 2 2 2 2 Acetic anhydride 2 2 4 2 3 2 2 2 2 2 Acetone 1 1 1 1 1 Alcohols 1 1 1 1 1 Alum 2 2 4 2 1 Alumina 1 1 1 1 1 Aluminum chloride 2 2 4 2 2 Aluminum hydroxide 1 1 1 1 1 Aluminum sulfate 2 2 4 2 2 1 Ammonia, absolutely dry 1 1 1 1 1 Ammonia, moist 4 4 4 4 4 4 4 4 3 4 Ammonium hydroxide 4 4 4 4 4 4 4 4 3 4 Ammonium chloride 4 4 4 4 4 4 4 4 3 4 Ammonium nitrate 4 4 4 4 4 4 4 4 3 4 Ammonium sulfate 3 3 4 3 4 3 3 3 2 3 Amyl acetate 1 1 2 1 1 1 1 1 Amyl alcohol 1 1 1 1 1 1 1 1 Aniline 3 3 3 3 3 3 3 3 Aniline dyes 3 3 3 3 3 3 3 3 Asphalt 1 1 1 1 1 1 1 1 Atmosphere, industrial 1 1 2 1 1 1 1 1 Atmosphere, marine 1 1 1 1 1 1 2 1 Atmosphere, rural 1 1 1 1 1 1 1 1 1 1 1 Barium carbonate 1 1 1 1 1 Barium chloride 2 2 4 2 2 2 2 2 1 1 1 Barium hydroxide 1 1 2 1 1 Barium sulfate 1 1 1 1 1 1 1 1 Barium sulfide 3 3 2 3 3 3 3 2 Beet sugar sirups 1 1 1 1 1 2 1 1 Benzine 1 1 1 1 1 1 1 1 1 1 1 Benzoic acid 1 1 2 1 1 1 1 1 Benzol 1 1 1 1 1 Black liquor, sulfate process 3 3 4 3 3 3 3 3 Bleaching powder, wet 2 2 4 2 2 2 2 2 Borax 1 1 1 1 1 1 1 1 1 1 1 1 Bordeaux mixture 1 1 2 1. 1 1 1 1 Boric acid 1 1 2 1 2 2 1 1 Brines 2 2 4 2 1 1 1 1 Bromine, dry 1 1 1 1 2 2 2 Bromine, moist 2 2 2 4 2 1 1 1 1 1 1 1 1 Butane 1 1 1 1 Butyl alcohol 1 1 1 1 Butyric acid 2 2 3 2 2 2 2 2 2 2 2 2 Calcium bisulfite 2 2 4 2 2 2 4 2 2 2 1 1 Calcium chloride 1 1 2 1 1 1 1 1 Calcium hydroxide 2 2 2 2 Calcium hypochlorite 2 2 4 2 Cane sugar sirups 1 1 2 1 1 1 1 1 Carbolic acid 2 2 2 2 2 2 2 2 1 I 1 1 Carbon dioxide, dry 1 1 1 1 2 2 2 2 Carbon dioxide, moist 2 2 3 2 2 2 2 2 Carbonated water 2 2 3 2 2 2 2 2 2 2 1 2 Carbon disulfide 1 1 1 1 1 1 1 1 Carbon tetrachloride, dry 2 2 4 2 2 2 2 2 Carbon tetrachloride, moist 1 1 1 1 Castor oil 1 1 1 1 1 1 1 1 1 1 1 1 Chlorine, dry 3 3 3 2 3 Chlorine, moist 3 3 4 3 2 2 2 2 2 2 2 4 2 Chloroacetic acid 1 1 I 1 1 Chloroform, dry 1 1 1 1 4 4 4 4 4 4 4 4 4 Chromic acid 3 3 3 3 3 Copper chloride 3 3 4 3 3 3 3 3 3 Copper nitrate 3 3 4 3 2 2 2 2 2 Copper sulfate 2 2 4 2 Creosote 1 1 1 1 1 1 1 2 I 2 2 2 1 2 Crude oil 2 2 3 2 I 1 1 1 1 Ethers 1 1 1 1 1 1 1 1 1 Ethyl acetate 1 1 2 1 Ethyl alcohol 1 1 1 1 1 1 1 1 1 Ethyl chloride 2 2 3 2 2 2 2 2 2 2 Ethylene glycol 1 1 2 1 1 1 1 1 1 1 Ferric chloride 4 4 4 4 4 4 4 4 4 4 Ferric sulfate 4 4 4 4 4 4 4 4 4 4 Ferrous chloride 2 2 4 2 2 2 2 2 2 2 2 2 4 2 2 2 2 2 2 2 Ferrous sulfate 1 1 3 1 1 1 1 1 1 1 Formaldehyde Formic acid 2 2 4 2 3 2 2 2 2 2 Freon 1 1 1 1 Fuel oil 2 1 I Fufural 1 3 1 Gasoline 1 1 1 Glue 2 1 1 Glycerol 1 1 Hydrobromic acid 3 3 4 3 3 3 3 3 3 1 1 1 1 1 1 1 1 1 Hydrocarbons, pure Hydrochloric acid 3 3 4 3 3 3 3 3 3 3 «. R a t i n g s . 1. Suitable for most c o n d i t i o n s of u s e . 2. Offers g o o d corrosion resistance. Can f r e q u e n t l y b e u s e d in p l a c e of a metal with a 1 rating w h e n s o m e o t h e r p r o p e r t y g o v e r n s its selection. 3. Fair corrosive resistance.
64 A
INDUSTRIAL AND ENOINEERINO CHEMISTRY
Copper Low-Ziinc Brasses High-Ziinc Brasses Phosph or Bronzes (Inhibit ied Admiralty Alumin um Brass) Alumin um Bronzes Copper-Silicon Alloys Cupron ickel, 10% Cupron ickel, 30% Nickel Silvers
Cupronickel, 30% Nickel Silvers
Aluminum Bronses Copper-Silicon Alloys Cupronickel, 10%
Comparative Corrosion Resistance"
Copper
I/EC
·
Low-Zinc Brasses High-Zinc Brasses Phosphor Bronzes (Inhibited Admiralty
CORROSION
4 4 4 4 4 4 4 4 4 4 Hydrocyanic acid Hydrofluoric acid 3 3 4 3 4 3 3 3 2 3 Hydrofluosilicic acid 2 2 4 2 2 2 2 2 2 2 Hydrogen 1 1 1 1 1 1 1 1 1 1 Hydrogen peroxide 2 2 3 2 2 2 2 2 2 2 Hydrogen sulfide, dry 1 1 1 1 1 1 1 1 1 1 Hydrogen sulfide, moist 4 4 3 4 3 4 4 4 3 3 1 1 1 1 1 1 1 1 1 1 Kerosene 1 1 1 1 1 1 1 1 1 1 Lacquers Lacquer solvents 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Lime 3 3 2 3 2 3 3 3 2 2 Lime-sulfur 2 2 2 2 2 2 7 2 2 2 Linseed oil 2 2 4 2 3 2 2 2 2 2 Magnesium chloride Magnesium hydroxide 1 1 1 1 1 1 1 I 1 Magnesium sulfate 1 1 3 1 1 1 1 1 1 4 4 4 4 4 4 4 4 4 Mercury Mercury salts 4 4 4 4 4 4 4 4 4 Methanol 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Methyl chloride, dry Mine water 3 3 4 3 3 3 3 3 3 2 1 1 1 1 1 1 1 1 Natural gas 4 4 4 4 4 4 4 4 4 Nitric acid 1 1 1 1 1 1 1 1 1 Nitrogen Oleic acid 2 2 3 2 2 2 2 2 2 2 2 4 2 3 2 2 2 2 Oxalic acid 1 1 I 1 1 1 1 1 1 Oxygen 2 2 3 2 2 2 2 2 2 Palmitic acid 1 1 1 1 1 1 1 1 1 Paraffin 2 2 4 2 3 2 2 2 2 Phosphoric acid 1 1 2 1 1 1 1 1 1 Potassium carbonate 2 2 4 2 2 2 2 1 1 Potassium chloride 1 1 l· 1 1 1 1 1 1 Potassium chromate 4 4 4 4 4 4 4 4 4 Potassium cyanide 4 4 4 4 4 4 4 4 4 Potassium dichromate, acid 2 2 3 2 2 2 2 1 I Potassium hydroxide Potassium sulfate 1 1 2 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Propane 1 1 1 1 1 1 1 1 1 Rosin 2 2 3 2 e 1 2 1 1 Sea water 1 1 3 1 1 1 1 1 1 Sewage Silver salts 4 4 4 4 4 4 4 4 4 1 1 2 1 1 1 1 1 1 Soap solutions Sodium bicarbonate 2 2 3 2 2 2 2 1 1 2 2 4 2 2 2 2 1 1 Sodium bisulfate 2 2 4 2 2 2 2 1 1 Sodium bisulfite 1 .1 2 1 1 1 1 1 1 Sodium carbonate 2 2 4 2 2 2 2 1 1 Sodium chloride 1 1 1 1 1 1 1 1 1 Sodium chromate 4 4 4 4 4 4 4 4 4 Sodium cyanide 4 4 4 4 4 4 4 4 4 Sodium dichromate, acid 2 2 3 2 2 2 2 1 1 Sodium hydroxide 3 3 4 3 3 3 3 3 2 Sodium hypochlorite 2 2 3 2 2 1 2 1 1 Sodium nitrate 3 3 4 3 3 3 3 2 2 Sodium peroxide 1 1 2 1 1 1 1 1 1 Sodium phosphate 1 1 2 1 1 2 1 1 1 Sodium silicate 1 1 2 1 1 1 1 1 1 Sodium sulfate 3 3 2 3 2 3 3 3 2 2 Sodium sulfide 2 2 4 2 2 2 2 2 2 2 Sodium sulfite 3 3 2 3 2 3 3 3 2 2 Sodium thiosulfate 1 1 3 1 1 1 2 1 1 1 Steam 2 2 3 2 2 2 2 2 2 2 Stearic acid 1 1 2 1 1 1 1 1 1 1 Sugar solutions Sulfur, dry 2 2 1 2 1 2 2 2 1 2 4 4 4 4 4 4 4 4 4 4 Sulfur, molten 1 1 1 1 1 1 1 I 1 1 Sulfur chloride, dry 1 1 1 1 1 1 1 1 1 1 Sulfur dioxide, dry 2 2 4 2 2 2 2 3 3 3 Sulfur dioxide, moist 1 1 1 1 1 1 1 1 1 1 Sulfur trioxide, dry 2 2 4 2 3 2 2 2 2 2 Sulfuric acid, 8 0 - 9 5 % 3 3 4 3 3 3 3 3 2 3 Sulfuric acid, 4 0 - 8 0 % 2 2 4 2 3 2 2 2 2 2 Sulfuric acid, 4 0 % 2 2 4 2 2 2 2 3 3 3 Sulfurous acid 1 2 1 1 1 1 Tannic acid 1 2 1 1 1 1 Tar 1 1 1 1 1 1 Toluene 2 4 2 3 2 2 Trichloroacetic acid 1 1 1 1 1 1 Trichloroethylene, dry Trichloroethylene, moist 1 1 1 1 1 1 Trichloroethylene, moist 2 3 2 2 2 2 Turpentine 1 2 1 1 1 ι 1 1 Varnish 1 1 1 1 1 1 1 3 1 1 1 1 Water, potable Zinc chloride 3 3 4 3 3 3 3 3 3 2 2 4 2 2 2 2 2 2 2 Zinc sulfate 4. N o t r e c o m m e n d e d . -, '· R a t i n g 4 far i n h i b i t e d a d m i r a l t y , 3 for a l u m i n u m brass. « R a t i n g 1 Î3r i n h i b i t e d a d m i r a l t y o n l y if at m o d e r a t e v e l o c i t y a n d for u n p o l l u t e d w a t e r ; o t h e r w i s e rating is 3.
CORROSION
I/EC
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A Workbook Feature
ment made of brasses containing more than 15% zinc is not generally satisfactory. Chlorides are more corrosive than sulfates Mercury and solutions of its salts cannot be handled by equipment made of any of the copper-base alloys. Acid salts and many of the metal salts which hydrolyze, act like dilute acid solutions and may be corrosive to some copper alloys. Hydrolyzing compounds such as ferric chloride and ferric sulfate, which also have oxidizing properties, are definitely corrosive to copper and its alloys. Salts having oxidizing properties, such as chromâtes, are not corrosive in neutral or alkaline solutions but are severely corrosive in acid solutions. Sulfides are more corrosive to copper and alloys high in copper content than to brasses such as yellow brass or Muntz metal. Gases
Copper and its alloys are not attacked by dry gases at room temperatures or lower, but may be attacked by moist gases. For example, acetylene forms an explosive compound with copper when moist. For this reason, alloys containing more than 6 5 % copper should not be used with the wet gas under pressure. Moist carbon dioxide is corrosive to brasses high in zinc, but can be handled by other copper alloys. Tin coatings are highly resistant to moist carbon dioxide and are often used on copper alloys. Moist chlorine gas is corrosive to all copper alloys. Sulfur dioxide and sulfur trioxide in the presence of moisture form sulfurous and sulfuric acid, respectively. Organic Compounds
Copper alloys are resistant to most· organic solvents such as acetates, alcohols, aldehydes, ketones, petroleum solvents, and ether. Copper alloys can be definitely corroded by chloride hydrocarbons, such as carbon tetrachloride and trichloroethylene, at their boiling points in the presence of moisture, unless the hydrocarbons are stabilized by a neutralizer. Of the copper alloys, cupronickel, 30%, offers the best resistance to moist chloride hydrocarbons. Other alloys can be tincoated. 66 A
Fresh Water
Deoxidized copper and red brass are the most common piping materials for carrying fresh water. Red brass is more resistant than copper to waters containing free carbon dioxide. Such water can dissolve trace amounts of copper from bare copper and red brass pipe. The dissolved copper may then combine with soap to cause blue or green* stains. A suitable water neutralizer will prevent such staining or, if necessary, the copper or red brass can be tin-lined. Hard water can be protective to copper alloys by the deposition of a lime film on the surfaces. There is, however, an increasing use of water softening systems in which the filmforming salts, particularly calcium bicarbonate, are changed to soluble sodium bicarbonate. When water containing such bicarbonate is heated above 140° F.,the bicarbonate breaks down chemically and releases free carbon dioxide, making the water considerably higher in corrosiveness. Thus, when a copper, watertube system is used, most satisfactory results call for the use of softened water at 140° F. and less, and a neutralizer to remove carbon dioxide is recommended. Sea Water
Copper and copper alloys are used extensively for the handling of sea water, as, for example, in ships and tide water power stations. Many standard and special alloys are used for this service, but the cupronickels are the preferred alloys. Copper alloys are chosen for this service partially because of their inherent corrosion resistance, but more because of their ability to form films of corrosion products that are resistant to erosion by turbulently flowing sea water. Of all the copper alloys, cupronickel, 30%, has the highest corrosion resistance and the best ability to withstand high water velocities. A close second is cupronickel, 10%, which was specifically developed for condenser-tube applications. Muntz metal is frequently used for tube plates in steam condensers because of the good mechanical strength and relatively low cost. Although resistance to sea water is
INDUSTRIAL AND ENGINEERING CHEMISTRY
good, some dezincification does take place. However, the plates are usually thick enough so that structural stability is not a problem. Inhibited admiralty metal offers excellent corrosion resistance to unpolluted sea water at moderate velocities. Aluminum brass has effective corrosion resistance for sea water that is polluted and it will withstand higher velocities than will inhibited admiralty. With phosphor bronzes the resistance to the action of sea water improves as the tin content increases. Petroleum Refining
Oil refinery heat exchangers require metals that are resistant to many types of natural waters—both, fresh and saline—as well as to many corrosive chemicals in the process vapors. Many copper alloys can be used for this type of application, with the brasses being most frequently chosen. At high temperatures, particularly over 400° F., cupronickel, 30%, tubes are more frequently used because of their superior strength and corrosion resistance. Red brass is also used extensively in tube and baffle plates, in refinery condensers, and for refinery acid-sludge lines. Steam
Copper and copper alloys resist the attack of pure steam. There is some chance of attack when the steam contains carbon dioxide, oxygen, or ammonia. Under these conditions, the steam itself will have little or no corrosive effect, but the condensate will attack copper alloys, particularly the high zinc brasses. Copper is frequently used in boiler feedwater heaters for low and moderate pressures and temperatures. Cupronickel, 30%, tubes are preferred for heaters involving high pressures and high temperatures.
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