Eleventh of a series of columns on corrosion testing describes procedures for concentration cell tests b y Mars G. Fontana cell corrosion is one C of the chief forms of localized corrosion, and it causes many failures.
To Millivoltmeter and often occurs in or Milliammeter a constant or identical environment. Nitrogen However, there are no definite or Concentration cell standardized field or laboratory testing corrosion is somemethods specifically for this form of times called solucorrosion in the chemical process indus- tion cell corrosion tries, as far as I know. If the readers and also crevice corof this column have information on rosion and deposit this point, I mould be very glad to have attack, because it often occurs in crevices and under deposits. These areas become anodes and corrosion proceeds. Surrounding areas become cathodes. Figure 1. Concentration cell corroLocalized attack is sion of silver coil often intensified bethe details of these tests. A good cause in most cases plant test or evaluation test is needed. a n u n f a v o r a b l e In most cases, concentration cell cor- area effect existsFigure 3. Experimental oxygen concentration cell rosion data are obtained in connection namely, a large ratio with, or incidental to, other types of of cathodic to antests, for example, localized corrosion odic areas. The two most common types of con- as those used to separate corrosion under a specimen holder or spacer. Concentration cell corrosion results centration cells are oxygen and ion test specimens O r to support a Coil from cells, or anodes and cathodes, set cells. Oxygen is depleted in the crev- Or tube; loosely adhering corrosion products that are permeable t.0 liquids; up on the surface of a single metal be- ice or stagnant solution and is usually under insulation; looseIy rolled tubcause of differences in the environment consumed because of the corrosion ing in tube sheets; and almost any in contact with this metal. This form reaction. h%etallic ions often build other situation where an electrolyte of corrosion is different from galvanic up in the stagnant area, thus creating- a becomes stagnant and can change or two-metal corrosion, which is asso- higher ion concentration here as com- its concentration as compared with ciated with digerent metals or alloys pared with the solution in contact with adjacent solution. Generally speakmost commercial metals and surrounding or adjacent ing, alloys are susceptible to concentration metal surfaces. cell corrosion. Particularly susceptible are those materials that depend on Concentration cell cor- “passivity” for corrosion resistance rosion can occur in gas- such as the stainless steels. keted surfaces such as flanges; lap joints such Figure 1 shows concentration cell as a riveted joint; holes corrosion of a pure silver heating coil such as porous melds; contact faces that are not after a few hours of operation. The liquid tight such as under silver lining of this vessel showed no washers, bolt heads, or screwed fittings; under attack because solids formed only on deposits that are permea- the heating surfaces. Figure 2 is a ble to liquids such as s a n d , sludges, m a r i n e growths; solids that deposit on heating surfaces or anv other “foreim” Figure 2. Corrosion on gasket surface of or n&metallic matxer: stainless flange spacers o r supports such Figure 4. Rack for gasket tests
OKCENTRATION
November 1955
INDUSTRIAL AND ENGINEERING CHEMISTRY
81 A
Corrosion
Special heat exchanger materials are well ksrown at Downingtown! Enamel-Lined Tubes. This stainless steel heat exchanger, with enamel-lined tubes, solved a serious set of problems which inheavy corrosion intermittent cluded high temperatures operation and a tight budget. It now operates at 150% of design capacity, at a temperature of 1200’ F.-and the owner reports trouble-free service from his Downingtown unit. Dimensions: 28” diameter x 10’ 0” long. Stainless steel shell. Tubes: 3%” O.D., lined with high temperature enamel.
.. .
...
...
Ampco 8 - D o w n i n g t o w n engineered Solid Nickel-This solid nickel reboiler these two fixed tube sheet benzene confor vacuum service-one of eight identical densers for export. Process conditions reunits fabricated for o n e customer-was quired copper alloy tube sheets, yet the engineered by D o w n i n g t o w n to use a customer did not want a gasketed joint minimum amount of scarce and expensive between tube sheets and shell flanges. So materials. The double tube sheet construction required special assembly techniques. w e welded the Am co 8 tube sheets diNotice the large nozzles, which were inrectly to the steel siells, thus savin the stalled with a minimum of distortion b dicost of alloy shells. Dimensions: ameter x 12‘0” long. Eighty copper tubes, !sing roper care and skill during weld! ing. d a d e of Vi‘‘ solid nickel. Dimen1 “ O.D. x 14 gauge. Ampco 8 tube sheets sions: 34“ diameter x 17‘ 0” long. Has 7/8”thick.Ampco 8 heads %”thick.Design 292 nickel U-tubes, 1” O.D. x 16 B.W.G. pressure is 7 5 psi o n shell and tube sides. Visit us at the Chemical Show-Booth 714
18‘
W e furnish complete thermal and mechanical designs, or fabricate to your plans. Send now for additional information.
Downingtown Iron Works, Inc. Downingtown, Pennsylvania New York Office: 52 Vanderbilt Avenue, New York 17, N. Y. HEAT EXCHANGERS
TOWERS
PRESSURE VESSELS
STORAGE TANKS
Division of: Pressed Steel Tank Company, Milwaukee 14, Wisconsin
STEEL A N D ALLOY PLATE FABRICATION
Manufacturer of Hackney Products
CONTAINERS AND PRESSURE VESSELS FOR GASES, LIQUIDS AND SOLIDS For further Information, circle number 82 A on Readers’ Service Card, page 111 A
62 A
good example of attack a t a gasket face. The inside surface of this stainless steel pipe shows practically no corrosion. Figure 3 shows. a n experimental oxygen concentration cell for laboratory investigations. By eliminating the gas bubbling devices, this same apparatus is used for other types of concentration cells. For example, a dilute solution containing metal ions is placed in the porous cup and a more concentrated solution in the other vessel. Another example is to place different concentrations of any solution in this equipment. Figure 4 shows a plant test rack for studying the problems presented by the corrosion shown in Figure 2. The gasket test materials are held between bolted strips of Type 316 stainless steel. Duplicate gasket specimens are used and they are separated by a third strip between the two outer strips. The gasket specimens are 2l/, inches long and extend about l/4 inch on each side. This rack developed the type of attack shown in Figure 2. Evaluation of these tests was made by estimating the percentage of the area attacked, measuring the depth of the pits, and by the condition of the gasket, and its ease of removal after test. Another test method consists of two disks held together by a bolt and nut of the same material. The facing surfaces of the two disks are machined with a slight taper starting from a :enter flat about l/z inch in diameter. This results in a tight center joint and a fine crevice near the center which increases in width as the periph3ry of the disk is approached. This irrangement is sometimes modified by Ise of flat strips instead of disks. Another method consists of laying In a horizontal metal specimen a small nile of sand, some sludge, a piece of isbestos or gasket material, a piece of “ubber, or any other material to be studied. This is, of course, placed in ;he corrosive under study. If sludges )r slurries are involved, a specimen is sometimes placed vertically in a con;airier with sludge settled on the bot,om and clear liquid over it. One end if the specimen is thereby buried in the dudge. Another method consists of nerely wrapping the specimen with string, cord, or rubber bands. Another type of test specimen consists of two rods, one containing a male
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Vol. 41, No. 11
nitroparaffin derivative
"Tris Amino" is short for Tris(hydroxymethy1)aminomethane. This chemical is unique. I t is the only tri-hydroxy molecule commercially available having a primary amine group. /CHzOH H2N-CCHzOH \CH~OH Tris Amino is a raw material undergoing a very wide variety of chemical reactions. The reactivity of Tris Amino makes it of unusual interest in chemical synthesis, since it contains a primary amine group and three primary reactive hydroxyl groups. Manufacturers of resins, synthetic drying oils, and surface active agents cannot afford to overlook the potential usefulness of Tris Amino as a raw material. Tris Amino reacts with higher fatty acids to form soaps with unusually strong emulsifying power. Relative high boiling point and low combining weight recommend the use of Tris Amino in preparation of cosmetic creams, textile specialties, cleaning compounds and many other emulsions.
CSC's new Nitroparaffin plant a t Sterlington La. is now in full production. Additional facilities for increased volume of NP derivatives are nearing completion.
i
6
0
8
@
@
@
@
8
8
8
@
8
9
9
8
8
PROPERTIES Molecular Weight Boiling Point, "C Melting Point, "C pH of 0.1M Aqueous Solution at 2 0 ° C Solubility in Water a t 20°C, g/lOO ml
I
i I I
See What Tris Amino
Market Development Dept. Commercial Solvents Corp. 260 Madison Avenue New York, 16, N. Y.
Can Do For You Fill in
Coupon Now 0
10.4
80
Other Aminohydroxy Compounds AB (2-Amino-1 -butanol) AMP (2-Amino-2-methyl-1-propanol) AMPD (2-Amino-2-methyl-1, 3-propanediol) AEPD (2-Amino-2-ethyl-1, 3-propanediol)
Now available in semicommercial quantities.
t ~ . e * e a e e t a
COMMERCIAL SOLVENTS I
121.14 2 19 to 220 IOmm 171-1 72
INDUSTRIAL
I I II
So I can further evaluate CSC Tris Amino, please send me detailed technical data and a sample. Name ....,_ Iwe Company Street city
i Zone-State
........................................................
I I
1
For further information, circle number 83 A on Readers' Service Card, page 111 A
November 1955
INDUSTRIAL AND ENGINEERING CHEMISTRY
83 A
Corrosion and the other a female thread. These are screwed together with or without gaskets or spacers. A different arrangement consists of stringing specimens on a rod and using spacers of different materials or sizes. A method developed in our laboratory involves a test specimen that is readily preparedand gives good results. A l / p X 4 inch strip is bent downwards on a large radius-just enough to obtain a slight curvature. It is then bent 180” back on itself in the opposite direction over a 1/2- to 1-inch diameter rod. The resulting “hairpin” is then squeezed together so the two ends are in firm contact. The original downward bend causes the tips to spring back slightly, thus forming a crevice. As in any testing method, an attempt should be made to simulate or duplicate as closely as possible the actual conditions. If lap joints are to be used, the specimen should be a lap joint; if nails or tie rods in wood are to be used, then construct similar samples; if screwed joints are contemplated, use such a joint as a specimen.
References and acknowledgment
Let’s talk “LOW ABSORBENCY” For perchloric acid fume hoods. Alberene Stone has a low absorbency factor of 0.15%. It’s essentially nonstaining. Easily cleaned. And readily machined for tongue and groove, watertight construction. Both of these features are absolutely essential for perchloric hoods - where thorough water flushing and removal is necessary to keep them deposit-free. Further, with Alberene Stone - the natural silicate stone whose surface goes all the way thru - the all-silicate mineral components resist chemical attack. Our engineers are ready to help you select or design perchloric hoods or other special-purpose hoods. Alberene Stone Corporation, 419 Fourth Avenue, New York 16, N. Y.
provides LOW ABSORBENCY protection Far further information, circle number 64 A an Readers‘ Service Card, page 111 A
84 A
’ INDUSTRIAL AND ENGINEERING
Figures 2 and 3 were supplied by E. V. Kunkel, Celanese Gorp. of America, Bishop, Tex., and they appeared in “Selecting Gaskets to Limit Corrosion of Stainless Steel Bolted Joints in a Chemical Plant” [E. V. Kunkel, Corrosion, 10, 260-6 (1954) 1. Figure 4 is from an International Nickel Co. bulletin titled “Corrosion.” The use of these figures is hereby gratefully acknowledged. Previous columns on corrosion testing : Types of tests, reasons for conducting tests, materials, and specimens Surface preparation, mewuring, weighing, and exposure techniques Duration of tests Plant exposures, effect of temperature laboratorycontrolled iemperature baths, and plant tests for heating surfaces Aeration and expression for corrosion rates Nitric acid testing of stainless steels Procedures for cleaning specimens after exposure Nomograph for converting corrosion rates and densities, and costs of materials Procedures for galvanic or two-metal tests 3tress corrosion
Date Dis-cussed April 1954 July June 1954 1954
August 1954 September 1954 October 1954 December 1964 February 1955 April 1955 June 1955
Zorrespondence concerning this column will b e ‘orwarded if addressed to t h e author, $6 EdiLOT. INDUSTRIAL A N D EXGINEERINQ CHEMISTRY, 1155--16th St.. N.W., Washington, 6, D. C.
CHEMISTRY
Vol. 47, No. 11
4
-
