A sea water pond on the Atlantic coast near Wilmington, N . C , used as a proving ground of marine corrosion by several metal companies.
The pond drained, the erosion testing apparatus is now in position for installing specimens of variously treated metals to be tested.
Corrosion Research Project at Kure Beach Test Station HARRY W . STENERSON, Industrial Editor A t Kure Beach, Ions-term research is soins on in metal corrosion in sea water from chemical action, galvanic current, and from marine organisms such as the Teredo.
Many alloys and protective finishes are
being tested under exacting conditions. A T KURE, Beach, near Wilmington, ** N. C , metals, alloys, andfinishesarc taking a form of punishment which scientific ingenuity could hardly simulate in any man-made laboratory. Some 19,000 specimens are exposed for years to sea water and to as corrosive and damaging an atmosphere as can be found anywhere
along the Atlantic Coast—to a sea and air that are brine-laden, humid, and variable in temperature, water, and wind velocity. Ordinary unprotected carbon steels crumble and flake off to the touch after exposure for a year or so to such conditions. On the same site, and not far from the
Specimen racks exposed with pond drained
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Ethyl Dow plant for extracting chemicals from the ocean at Cape Fear, metals, coatings, and plastics are submerged in the briny stream which feeds that operation. In this manner manufacturers can determine the extent of their resistance to fouling, corrosion, and erosion, and thus make valuable contributions to ship construction and operation. The companies engaged in this important research project, which they call the "Proving Ground of Marine Corrosion", a term which only partly describes the work done there, are The International Nickel Co.; the Carnegie-Illinois Steel
Piling test specimens at intake basin
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Corp.; and the magnesium division of The Dow Chemical Co. In addition, hundreds of other companies send in speci mens of metals and coatings for testing. The studies are cooperative and there is a free interchange of data and ideas for mutual benefit. During the first week in June, the three companies mentioned invited a group of editors of technical and industrial journals down to Kure Beach for a first hand view of this research which has been under way for 10 years. Through personal inspec tion they were able to determine the value of the long-term testing program in terms of actual results. Participating in the discussion were F. L. LaQue, in charge of the corrosion engineering section, Inter national Nickel Co., J A. Peloubet, de velopment engineer η magnesium divi sion, Dow Chemical Co.; Ewart S. Taylerson, research engineer, Carnegie-Illinois Steel Corp.; and W. F. Clapp, Wm. F. Clapp Laboratories, Duxbury, Mass., specialist in marine growth. Headquarters were maintained at the Hotel Bame, Caro lina Beach. Comparative Resistance
The strongly corrosive action encoun tered at the atmospheric testing station was withstood successfully by specimens of stainless steel, particularly where the chromium and nickel contents ran high; by aluminum, nickel, and magnesium alloys. Ordinary carbon steels and irons probably fared the worst, especially when copper content was as small as 0.004%. Samples containing such small amounts of copper exposed for 1.5 years or more rusted away in layers. The best perform ances were obtained from steels with nickel contents of 0.5 to 5 + % , in some instances with copper up to 1%, and from other more complex steels containing chromium, nickel, copper, and molyb denum in different combinations. Some of these better steels lost only 10 grams through corrosive action in 3.5 years, while other steels lost over 100 grams in the same length of time. Samples of steel with sprayed or "metal lized" coatings resisted well the severe conditions at Cape Fear. In this group were specimens so coated with zinc, alu minum, and lead. Hot-dipped zinc coat ing also afforded excellent protection to steel, as did special coatings of nickel-zinc alloys. While galvanized coatings as light as 0.75 ounce per sq. ft. (including coat ings annealed after galvanizing) were pro viding good protection after 4.5 years, it was evident that the heavier coatings (up to 2.5% ounce per sq. ft.) would be more durable. Samples of steel coated with baked phenolic varnishes which had been left outdoors for two years showed only slight chalking on their surfaces. "Plstn and alloy cast irons turned a J $ep reudish brown in this atmosphere but re sisted corrosion well as compared to the ordinary unalloyed steels. V O L U M E
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Typical section of steel weld after service for 6 years
Stainless steels were in excellent condi tion after years of exposure, and in the severe weather at the testing station those containing at least 18% chrome plus nickel and molybdenum were the most re sistant. Mr. LaQue said that while 13% chrome steel might pass a salt spray test, it would show definite rusting under the punishment inflicted by the weather at the Kure Beach testing lot. Interesting tests were made with "buttons" of stainless steel combined with other metals, consist
ing of washers of various sizes piled in pyramid fashion so that each sample left a circular margin. It was noted that with Monel and stainless forming a galvanic couple, stainless fared even better than it did by itself in these tests. Similar results were observed in combinations of stainless steel with lead, zinc, copper, brass, and aluminum. Surprisingly enough, these other metals did not appear to suffer greatly from their contact with stainless steel in this atmosphere.
Racks exposed with pond drained
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Monel metal, a natural alloy which con sists of about two-thirds nickel and onethird copper, was selected for the con struction of many of the test frames at the atmospheric station. Others were made of 18-8 stainless steel. These frames served as much as a test against seaside conditions as any of the specimens they supported. Inconcl, consisting of 8 0 % nickel, 7% iron, and 13% chrome, sur vived 4 years of exposure in excellent condition and appeared to do better than pure nickel which assumed a relatively dull appearance. Inconel finds an important place in equipment used ! ι the manu facture of dyes and certain organic chemi cal processing, fatty acids, pharmaceuti cals, vegetable oils. In addition to corro sion resistance, it withstands temperatures up to 2,100° F. Chromium-nickel and chromium-nickelmolybdenum stainless steels were exposed in the form of panels joined by spot weld ing. The welds and laps were all in good condition and exhibited only a slight de gree of staining after 4 years. In the magnesium racks where Dow Chemical Co. is conducting atmospheric tests of this metal, many panels were in good to excellent condition after exposures of from 3.5 to 10 years. As in the in stance of other specimens, the magnesium panels are insulated with small spindle ceramic insulators against moisture pock ets and galvanic effect. T h e magnesium alloys in most cases were coated with a thin, dull film wrhich resisted corrosion.
D i e castings, sand castings, sheet, and extrusions of magnesium are being tested on the atmospheric lot at 800 to 80 feet from the ocean. Most satisfactory among the magnesium specimens are Dowmetal R die castings ( 9 % aluminum; 0.2% manganese; 0.6% zinc; balance mag nesium) and Dowmetal J-lh sheet (6.5% aluminum; 0.2% manganese; 1.0% zinc; balance magnesium).. Sheet and extrusion of magnesium which had been exposed for 3.5 years showed development of the pro tective coating referred to and appeared to be substantially the same as when set out. Some paints of the colored enamel and lacquer type applied to sheet magnesium panels showed chalking after 3 years' ex posure to the intense sunlight while aluminized varnish stood up very well. This is actually a test of the paint as well as the magnesium under it. Preliminary treat ment of the magnesium sheets prior to painting involved a dip in hydrofluoric acid, followed by boiling in sodium dichromate. This treatment provides, good paint anchorage in the same manner as the common phosphate coatings applied to steel. Very good corrosion resistance was ob tained in bare or painted cast magnesium bars which contained 6% aluminum, and 3 % zinc (Dowmetal II). The aim in future casting, Mr. Peloubet said, would be toward high-purity alloys yielding even better corrosion resistance—such as is now obtained with the standard wrought alloys of controlled purity.
Bars and tube brackets on erosion testing disk exposed with pond drained
Dow has brought in a great variety of magnesium aircraft parts for testing at the Cape Fear Station, including many welded sections, large castings, tail stabi lizers and booms, bomber wheels, and fuselage sections. In this heavily brineladen air, which destroys plated automo bile parts and covers less resistant objects outdoors and indoors with a layer of rust, the magnesium airplane castings and assemblies showed no corrosion. Early tests of welded magnesium parts showed a susceptibility to cracking after exposure. The cracking was due, the D o w engineer said, to locked-in welding stresses and the effect can be avoided through the use of simple stress-relieving measures. Annealing of welded parts for one hour at 265° t o 400° F.—depending upon alloy composition—prevents subsequent crack ing. Paint coatings alone offered not more than 5 months' protection before cracks appeared, so should not be considered as replacing the stress relief. Magnesium tail booms when first built for experimental P-61 airplanes exhibited cracking due to lack of relief of the lockedup welding stresses. However, properly stress-relieved booms subsequently built have proved to be satisfactory even under flight loading conditions. Various metals were exposed in contact with magnesium to the intensely corrosive conditions near the sea at Kure Beach in order to determine what alloys could be safely used at such junctions. 52S alumi num yielded the least galvanic (battery) effect on the magnesium while such dis similar metals as brass, copper, and steel were among the worst. The galvanic corrosion present at the junction of magnesium with steel bolts can be reduced by cadmium-plating the bolts and substantially eliminated through the use of zinc plating (galvanizing). Gal vanizing also protects the steel better than cadmium plating does in this seacoast atmosphere. Galvanic Attacks
Aluminum rivets of 28 and A17ST alloys cause galvanic attack on magnesium— eventually resulting in more corrosion of the aluminum due to the presence of alka line magnesium hydroxide. Paints retard, but do not prevent this cell action. The use of 56S aluminum rivets in magnesium has been satisfactory in that no corrosion takes place, whether the part is painted or left bare. T h e answer is proper match ing of metals to prevent galvanic action. Interesting results were obtained with household fly screen materials including Saran, and stainless steel as well as most of the more common insect screen ma terials. Saran, thermoplastic resin, was in good condition. The type 316 stainless samples appeared to be the most durable. D r . Clapp discussed the various tests being conducted at Kure Beach on pro tective coatings and methods and ma terials which are used to control the growth
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of marine organisms. Among these are various alloys, paints, greases, plastics. Samples of propeller blades and tests of similar alloys submerged in salt water were generally found to be less fouled when the copper content was comparatively high. Marine organisms were found plentifully on metals low in coppers, while some appeared on test specimens made of pure or nearly pure copper. Various Finishes Tested
Because of the proved value of copperas an antifouling agent, there is a definite demand for green anti fouling paints due to the genera] belief that color indicates a high copper content. The green color, however, is no indication of whether or not copper is present. Actually a white antifouling paint would be the most desirable because other factors being equal the fouling organisms thrive best on the clarker colors. Tests also appeared to indicate that antifouling materials which break down at an even rate are most desirable, since the failure of the surface finish provides a very insecure foothold for the fouling organisms. Dr. Clapp drew a number of metal panels which had been covered with various types of greases and lubricants to demonstrate this theory. After several weeks of exposure the grease-covered panels were found to be comparatively free from fouling, demonstrating his conclusion that a material which does not provide a firm, more or less permanent base, is desirable in controlling fouling. Lanolin, a wool fat, proved to be a failure in this respect, however, and did not retard marine growth. Various plastics and coal-tar products are also being tested to determine their effectiveness in providing protection from the fouling of ships' hulls and structures in salt water. A number ^f acrylic resin panels supplied by Rohm & Haas, Philadelphia, for testing purposes had been submerged in the testing pond and upon examination were found to be in the preliminary stage of fouling. These panels had been in the water for only 3 weeks. They were in various shades ranging from white to very dark blue for the purpose of determining the effect of color on the different species of marine organisms present. In this brief period of time, the darker colon* were much more heavily fouled than the lighter shades with the white fouled least of all. In another Plexiglas panel test the transparent sample was as heavily fouled as the darkest colored panels. This was also true of glass and other transparent material.
Oysters on intermittently immersed racks
pest. Soine species of teredo are capable of drilling through wood at the rate of 1 inch per week. In two months they may construct tunnels J8 or 10 inches in length. When present in large numbers they frequently completely destroy large piling 12 or more inches in diameter in 3 months. The teredo is apparency not affected by arsenic and many other toxic materials. In Dr. Clapp's opinion itbs tunneling in wood is not for the purpose of obtaining food but solely for protection. Close relatives of the teredo form similar tunnels in marble, shale, or poor concrete for the same purpose. Solid blocks of various tppes of paraffins and waxes arc submerged at Kure Beach in order to determine into just what materials the "ship worm" cam drill. At the present time coall tar creosote is the only preservative whiih has a proved value in controlling attack by teredo. In Dr. Clapp's opinion this is not due to the toxicity of this preservative, but rather to the fact that it renders Uhe very minute cutting teeth of the teredo's drilling apparatus ineffective. Incidentally, the dental equipment of the teredo is marvelously efficient. When the teeth are worn down by arduous drilling the animal is capable of growing a new row of denticles during a rest period of only a few hours. Facilities at Kure Beach for antifouling research duplicate conditio«ns encountered by a vessel at dock or in motion. Sea water is pumped "as is" into a testing reservoir or pond where it flows past the specimens at a constant, uniform rate of 2 feet per second. Metals anad other specimens are fastened with WTonel bolts and
Damage by Teredo
The teredo, a mollusk which drills into wood and some other materials and which has been known to mariners for centuries as the "ship worm", has become the object of special attention of many researchers. Dr. Clapp's work has brought to light some valuable data regarding this destructive V O L U M E
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phenolic insulators to Monel or creosoted wood racks, and the racks are submerged at a depth of 3 to 4 feet. Suspension is made from parallel wood beams, supported on piling. Marine organisms attach themselves to practically everything racked as they would to hulls of ships in port. Corrosive influences get to work on metals and alloys in the same manner as they bring about deterioration of submerged parts of a vessel. Corrosion and erosion, especially of pump impellers, propellers, and condenser tubes, of course, proceed when a ship is plowing its way through the sea. To meet these conditions the corrosion engineers have devised revolving disks which spin constantly under water at high speeds, and to which they have fastened ship parts exposed to high velocity sea water action. The effect on the metal samples in the form of tubes, rods, or flat bars is highly destructive. According to Mr. LaQue, this apparatus permits observations of the behavior of materials under as severe conditions as are likely to be encountered in marine service. By precise measurements of damage, the probable result of many years' service can be determined within a few weeks. No test in the reservoir is conducted for less than 6 months, and some metals have been submerged for as long as 10 years. Steel piling is tested for corrosive action by Inco and by several steel makers. The piles are driven deep into mud at the sea water intake basin fronting the plant so as to take advantage of tides. Progress of the corrosion is measured by the decrease which* occurs in the steel's thickness, both above and below the water. 1163
