Ideas
Exchange
Column
l/EC's features bring in lots o f f a n m a i l . Readers w a n t information, and they pass along ideas. Ideas Exchange Column is a careful screening o f this correspondence. This is not a place f o r praise or criticism; it is a source o f technical questions a n d their factual answers.
tion purposes, on our next trip to the States?
Corrosion in CO2 Production DEAR COCK:
MESSRS.
LUCE
AND
PEA-
We have in operation a locally made plant for producing CO2 which works on the monoethanolamine method. All of the different parts of the equipment have been built of low-carbon steel or black iron, and in order to protect the internal surfaces, some copper sulfate and potassium iodide are used, in low concentrations dissolved in the monoethanolamine solution, as recommended in the literature. Lately, some severe corrosion was observed in heat-exchanger pipes (water/m.c.a. solution) (m.e.a. solution/carbonated m.e.a. solution) and also in pipes of the reboiler where C 0 2 is liberated from the amine by heat. When each part of the equipment was examined to investigate the reasons for this heavy corrosion, some significant difference in potential was observed between pipes, heat-exchangers, and reboilers and also between each piece of equipment and ground (potential 0). In some cases, that potential difference was of the order of 2 mv,—sometimes on the positive and sometimes on the negative side. Considering this fact an abnormality, our first reaction was to connect the whole system to ground, but as this is a superficial approach to the basic problem, we request your advice on the following questions: 1. Could ground connections eliminate corrosion due to galvanic currents? 2. Is 2 mv. significant from a corrosion point of view? 3. Is there information in the literature that could help us cope with corrosion problems in monoethanolamine C 0 2 plants? 4. Is there literature on cathodic protection, which shows whether it is feasible to protect our plant by this method? 5. Whom could we interview personally in the U.S.A., for consulta-
J. A. MILLER, The Coca-Cola Export Corp., Sucursal Argentina, Buenos Aires, Argentina
Mr. Peacock's
answer:
Thank you for your letter pertaining to the corrosion you arc encountering in producing CO·) by the monoethanolamine method. Our comments will perhaps not be as detailed and complete as you may like in that we are not aware of the many details of the particular problem. By this we mean such items as exact service conditions (concentration, temperature, velocity, and aeration), how and where corrosion is manifesting itself on each particular piece of equipment, whether the severe corrosion is strictly a recent problem, materials from which each piece of equipment is made (lowcarbon steel, black iron or combinations thereof), whether it has definitely been established that the only type corrosion being encountered is galvanic corrosion, and location of the various pieces of equipment with relation to each other. As you can see, there are many facts that must be considered to provide detailed comments pertaining to the most economical solution to your problem. A book that wc highly recommend concerning corrosion and its various aspects is, "Corrosion: A Compilation" by Mars G. Fontana. This book consists of Dr. Fontana's monthly corrosion columns which appeared in INDUSTRIAL AND ENGINEERING CHEMISTRY over a period of
10 years and describes in detail the various forms of corrosion, how they can be recognized and eliminated, in addition to corrosion data concerning many materials of construction. The following comments pertain to the questions listed in your letter: 1. We seriously doubt that a
ground connection would eliminate the corrosion taking place due to galvanic currents. By grounding, you do not eliminate the cell action but assure yourself it is taking place by actually creating a galvanic couple which is the opposite of what you want to accomplish. It is likely, however, that if there is a feasible method of insulating the respective pieces of equipment, the cell action could be eliminated and possibly arrest the corrosion. 2. Two millivolts could be significant from the corrosion aspect depending upon specific details previously mentioned in addition to the type of meter used to measure the voltage. A good, sensitive, high resistance meter should be used to measure accurately the relatively small potential difference to be absolutely certain the measurement is correct. 3. Unfortunately we cannot cite any literature references pertaining to corrosion problems in monoethanolamine CO2 plants. 4. Corrosion magazine published by the National Association of Corrosion Engineers is perhaps the best reference we could recommend concerning literature on cathodic protection. However, most articles on cathodic protection in this monthly magazine pertain primarily to protection of pipe lines, cables, dock structures, ships, and water tanks rather than process equipment. But we do not know any reference on cathodic protection that is mainly concerned with an application similar to yours. 5. As it appears you may have somewhat of a complex problem, it is possible there may be a less expensive corrective measure than cathodic protection if the minute details were known. The fact that you stated, "Lately, some severe corrosion was observed . . .," indicates there may have been a slight process change of which you may or may not even be aware. This could be contributing V O L . 52, N O . 7
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IDEAS to the excessive corrosion presently being encountered. For consulta tion purposes, we would recommend Dr. Mars G. Fontana, Chairman of the Department of Metallurgy, Ohio State University, Columbus, Ohio. Dr. Fontana has a wealth of practical corrosion experience from organiza tions throughout the world and is quite well known in the corrosion field. However, to enable him to assist you in solving your problem whether it be by cathodic protection or other means, we are sure he would need many details such as those de scribed earlier in this letter and per haps a few additional details which we may have omitted.
Skin, a flexible stainless steel which can be used as a sandpaper and is presumably recoverable. Can you supply the manufacturer's name? The last paragraph under the heading "Acrylic Resins" refers to several new polymers and copolymers and I would like to have information concerning the availability and sup pliers of these materials. J. W. BROCK, Technical Planning Manager, Paints Division, Cana dian Industries Limited, Box 10, Montreal, Que., Canada
A.P.A. PIGMENTI bm, Via S. Martino
61, Genoa Editor's
Note:
There is : The Lead Industries Association 60 E. 42nd St. New York 17, Ν. Υ. Attn. : Mr. E. J. Mullarkey
1.
Dragon Skin is manufactured by : Red Devil Tools, Union, N. J. Suppliers of these polymers are :
Our error. We do know the dif ference between a proton and a neutron.
a.
Sampling System
b. c. d.
e.
Polyaldehyde Resin, Shell Development Co., Emery ville, Calif. Sunstar-Aldehyde Starch, Miles Chemical Co., Elk hart, Ind. Epoxy Novolac—X 2638.3, Dow Chemical Co., Mid land, Mich. Ethylene Maleic Anhydride Copolymer, Monsanto D X 840, Monsanto Chemical Co., Springfield, Mass. Polycarbonate-Lexan, Gen eral Electric Co., Schenec tady, Ν. Υ.
Polyethylene Shields DEAR S I R :
Protective Coatings DEAR S I R :
We always look forward to the annual article which you publish by Dr. Harry Burrell which reviews the developments of the past year in protective coatings. The article [I/EC 52, 59A (January I960)] mentions some de velopments with which I am not familiar and I would like to obtain references to the source of the infor mation. In the last paragraph of the article reference is made to Dragon
T. FRIEDMAN, Physicist, Aerojet-Nucleonics, Box 77, San Ramon, Calif.
STANTON
Editor's
DEAR S I R :
Please advise if there is an Ameri can Institution (such as the "Zinc Development Association" in Great Britain) that gives information on the use of lead for the making of pig ments or other chemical products. We have an important pigment factory in Genoa and we use lead and zinc in large quantities.
2. The hydrogen (and other nuclei) of the polyethylene, slows down high energy neutrons not pro tons. These slowed down neutrons are then absorbed by the boron nuclei. The hydrogen nucleus is it self a proton with a mass essentially equal to that of the neutron which is why it is a better neutron "scatterer" than other heavier nuclei. Where was your nuclear consultant?
Dr. Burrell's Reply:
2.
Lead Association
EXCHANGE
The report "Get the Lead Out of Your Submarine" [I/EC 52, 34A (May I960)] contains two misrepre sentations. 1. The use of polyethylene will not make it possible to decrease the amount of lead shielding around a nuclear reactor. Lead is used to absorb gamma radiation and is rela tively ineffective (per unit weght) as a neutron shield. Polyethylene and other light hydrogenous ma terials (such as water) are effectively used to slow down and absorb neu trons but arc quite inefficient gamma ray shields (on a per unit thickness basis) compared to materials such as lead.
Note:
DEAR M R . W A L L :
I enjoyed reading your article "New Developments in Process Analysis Instrumentation" [I/EC 51, 53A (August 1959)]. I am most interested in obtaining a reprint of Frank Karasek and Buell Ayers' article, since this problem of injecting small samples (especially gas) contin uously has been bothering us here for quite awhile. We have built a few sampling systems which we dis carded and now are in the middle of building a new one which, we hope, will do the trick. Could you please advise as to the availability of a reprint of this article? S. SIDEMAN, Israel Institute of Tech nology, Department of Chemical Engineering, Haifa, Israel Mr. Wall's Answer: I suggest that you write directly to either Frank Karasek or Buell Ayers, Phillips Petroleum Co., Bartlesville, Okla., for a reprint of their article describing their small chromatograph sample valve. You may also be interested in knowing that Greenbriar Instruments, Roncenverte, W. Va. have been li censed by Phillips to manufacture their high speed chromatograph and are offering for sale both complete instruments and components. You can obtain Phillips' small chromato graph from them. VOL. 5 2 , N O . 7
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