by Mars G. Fontana
part two of a description of Tthe isInternational Nickel Co. corHIS
rosion test station located near Wilmington, N. C. Area 3 is inside the building where tests on sea water pumps, corrosion fatigue, salt spray tests, and rotating spindle tests occur. The pump tests include 1. An investigation to see if it is practical to coat an impeller and pump casing with liquid neoprene in order to arrest corrosion 2. A comparison of modified Type I Ni-Resist, Worthite, and aluminum bronze sea water pumps 3. A test of mechanical seals versus ordinary graphite impregnated or flax pump packing materials 4. Tests on wear rings made from S hlonel, Monel, titanium, Hastelloy C, and inert materials such as hard rubber and various plastics.
Figure 1.
Rotating spindle tests
Tapered tensile test specimens for corrosion fatigue tests are rotated a t 1400 r.p.m., and sea water is permitted to flow on their surface in sufficient quantity t o keep them wet at all times. One end of the test specimen is loaded by the use of a linkage and bearing arrangement so t h a t a continuous stress is applied on t h e end of the test bar throughout the test period. Loading can range from 5000 to 35,000 Ib. per sq. inch and some materials have completed as many RS 100 x l o 6 cycles. Four spray mediums are used in cabinet t e ~ t s - 3 ~ ~NaCl solution, 20y0 NaCl solution, actual sea water, and synthetic sea water. I n 1955 c- For further August
general, no correlation is observed between the spray cabinet tests and tests in the actual marine atmosphere 80 feet from shore. Figure 1 shows the arrangement for rotating a disk specimen at different speeds in sea water. The outer edge of the rotating disk corrodes to protect the inner surfaces of the disk on all nonferrous materials. Ferrous metals are entirely reversed-the inner surface corrodes while the outer surface near the edge of the rotating disk is completely protected and suffers no discernible corrosion. This can easily be explained on bases of potential gradients across the surface of t h e test specimen, differential aeration effects, and the polarization characteristics of the metals under study. Other tests that have been completed or are under way are ( a ) the size relationship between anodic and cathodic areas on specimens of different diameters, ( b ) a study of the current (d.c.) necessary to stop the corrosion of rotating disks in sea water which is of particular interest since, if practical, iB may be useful in protecting impellers in sea water pumps, and (c) a study of the rate of corrosion of machined versus asrolled surfaces on nonferrous metals. Area 4, inside the building, is where jet tests and polarization studies are made. The jet test consists of squirting a stream of water on a metal specimen, l/4 inch from the orifice. Jet stream velocity can vary from 4 to 18 feet per second. Entrained air is usually maintained a t 3% b y volume. Area effects are a factor in the test because the area of the metal where the jet impinges b e come the anode and the remainder of the specimen the cathode. Other studies include effect of filtered and unfiltered natural sea water. Figure 2 shows apparatus for polarization studies on metals and alloys, one of the most important fields of study a t Harbor Island.
Figure 2.
The apparatus consists of a battery of 22 units which receives sea water from a 3000-gallon rubber-lined constant level tank under a &?-foot head. The flow through each test unit is controlled on the inlet side with a diaphragm type valve. This valve in conjunction with a weir box and hook gage provides for accurate control of water velocity in each test unit. The inner hard rubber body of each test unit is milled so as to provide a support for electrodes or test pieces which measure 2’/8 x 13/le X inches. When in place, these specimens form the walls of a channel through which sea water can pass. The channel measures */4 inch wide X 1 inch high. The nature of this water path is such that with the rates of flow that are used, from 0.5 to 13 feet per second there is considerable turbulence within the test chamber. Accessory equipment includes gaskets, backup plates, and clamps for holding the specimens in place. All units are electrically insulated from the surroundings b y hard rubber fittings. Electrical connections to the test pieces are made through the use of sharpened contact screws which pass through insulated pieces on the clamps and bear against the outer surface of the test pieces. Use is made of the numerous resistors, instruments, and switches on the electrical control board whenever polarization studies are under way.
INDUSTRIAL AND ENGINEERING CHEMISTRY information, circle number 86 A on Readers’ Service Card, page 115 A
Apparatus for polarization studies
85 A
*
Corrosion
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- $475.00
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+
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11 ithotit u o l i c e . Piirer I.0.b. j n r l o v ) .
SEE YOUR -hp- REPRESENTATIVE OR WRITE FOR COMPLETE DETAILS
HEWLETT-PACKARD COMPANY 3343rJIPage M i l l Rd. Palo Alto, Cal., U.S.A. Field representatives in all principal areos C a b l e "HEWPACK"
ELECTRONIC MEASURING INSTRUMENTS
~
*Wifh fronsducers Circle No. 88 A on Readers' Service Card, page 115 A
88 A
Each circuit is supplied b y completely filtered direct current from separate selenium rectifiers. The potential of metal is determined by measuring a voltage difference between the metal and the calomel half cell by the use of a potentiometer. The calomel half cell maintains a constant known potential and serves as a reference point to which the potential of any metal may be referred. A great number of investigations can be conducted nith this apparatus to predict the amount of current necessary to protect steel piles or a ship's hull in sea water and to establish the advisability of roupling dissimilar metals together in sea water. Area 5 to the left of the main building is where piping and valves are tested under actual conditions. These tests have been in operation since 1947. Sea water is received a t a rate of 1000 gallons per minute. The system i s composed of two sections, one is made up of pipes from 1 to 2 inches in diameter, while the other is made up of pipes from 1 to 3 inches in diameter. Sea water flow is controlled and maintained a t predetermined flow rates by means of a number of valves, orifice plates, and manometer gages located a t strategic positions throughout both sections. Flow rates are set a t values between 10 and 15 feet per second. At present, the test is run on a 5-day operational schedule, 24 hours a day. Materials that have been or are a t present under test are aluminum brass; aluminum bronze; Ampco 5 ; 90-10 cupronickel (different iron levels) ; 70-30 cupronickel (diflerent iron levels) ; Yoloy; aluminum and its alloys: titanium; steel, bare and galvanized; cast iron; wrought iron, bare and galvanized; laminated fiberglass; and other experimental alloys. The primary aim is to find new and improved piping materials, but aspect9 related to the corrosion that occurs in these systems are also under study-i.e., the advantages of a long radius elbow versus the short radius elbow in minimizing the effect of turbulence; a study of the corrosion that occurs a t heat-affected zones due to welding and brazing operations; corrosion of pipe materials in stagnant sea water, such as might occur in dead end systems, such as fire mains.
A number of different types of sea water valves are being tested, such as globe, gate, diaphragm, and Y valves. Although each has a particular application, most show one or more weaknesses, Early tests indicated t h a t valve seats and disks were subject t o early failure. This problem was solved by specifying either Monel, S Monel, titanium, or nylon for this critical area. Valve stems have given trouble from time to time, but by specifying higher alloyed materials this problem is now of minor importance. Surprisingly enough, while valve manufacturers will meet specifications for the internal parts of a valve, very few seem to recognize the need for better materials for such miscellaneous items as valve handles, nuts and bolts for gland supports around valve stems, and the nut which holds the handle t o the stem. Many of these parts, which seem too small to be worth consideration, cause considerable trouble for the maintenance and repair crews early. Area 5 also contains a 600 footlong sea water trough with a flow velocity of 2 feet per second. Galvanic and other studies are carried out here because little fouling occurs in moving water. Maximum length of exposure is 2 years; longer times do not provide additional information. Area 6 covers the remainder of the main building. Scaling and corrosion tests are being conducted in actual evaporators for making fresh water from sea water. The laboratory carries a stock of 228 different nietttls and alloys for corrosion test spool specimens. Of particular interest is a balance for weighing specimens to 20 lb. with an accuracy of 1/60,000ounce. The machine shop i s well equipped. The Museum contains 1800 catalogued specimen6 displayed so t h a t effects of composition or velocity can be seen a t a glance. The wood samples showing marine borer attack are quite spectacular. The tremendous amount of data obtained in these testing stations i~ summarized by the Corrosion Engineering Section of Inco in New York City and is available. Correspondence concerning this column will be forwarded if addressed t o t h e author, cfo Editor. ISDUBTRIALA N D ENUINEERINUCHEMIBTRY, 11,56-1Bth R t . , V.W., Washington 6, D. C.
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
Vol. 47, No. 8
