Vacuum melting technipues, shown in these three pictures, are now practiced commercially
New and improved production techniques, greater demands in sew ice any aspects of stainless steels are investigated and although many of the studies, notably in space technology, have no immediate interest to the chemical industry, future benefits will certainly accrue. Production procedures which a few years ago were far from reality are now practiced commercially, and entirely new techniques are approaching large-scale operation. Critical service demands have been a major contributory factor to these advances, and as a result the chemical industry will have available better quality steels with better corrosion resistance. This article covers developments occurring in 1962. Considerable effort is being devoted to studying selective corrosion. Anodic polarization and other means of effecting passivity appear promising and will probably broaden the scope of stainless steels. Cryogenic uses are expanding rapidly and in addition to stainless steels which meet the necessary toughness and high strength requirements, the relatively new and less costly nickel-cont”ainingsteels are being emphasized.
M being
50
Corrosion
The most serious weakness of stainless steels is their poor resistance to solutions containing chlorides which account for most failures such as stress corrosion cracking and pitting attack. Means for predicting and combating such failures have received much recent emphasis. Maintaining a state of passivity increases chloride resistance. Various means of producing a passive condition are being investigated, including anodic protection, cathodic protection, and use of surface active agents. I n anodic protection, used (7A) to control cracking in sulfuric acid-chloride solution, passivity was maintained even at high chloride contents by controlling the current density of the cell. This observation is important because it showed that anodic as well as cathodic currents can stop cracking. Cathodic protection is also effective in controlling corrosion by inducing passivity, even under difficult circumstances-e.g., where selective corrosion of a sensitized stainless weldment by sulfuric acid was largely curtailed with an electric current
I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
pe yformame, and expanded
( 7 7.4). I n a study (3A) of passivity breakdown in various stainless steels, several surface active agents displayed inhibitive characteristics. Ultimately, basic polarization studies should prevent many costl) failures by determining the amount of current needed to maintain passivity. By comparing polarization curves of austenitic stainless steels and other alloys with those of the component elements, a new interpretation (QA) for corrosive resistance and development of alloys is presented-Le., that passivity can be determined from a study of the components. Such work can have a far-reaching effect on future developments in corrosion. Selective Corrosion. The susceptibility of stainless steels to selective attack still remains a primary concern and more development work will undoubtedly reduce the enormous costs attributed to this problem. Stress corrosion cracking is typical (8A) and much additional work is reported, including a detailed review ( 2 4 ) of several basic concepts which contribute to proper underThe standing of the problem.
Some uacuum-melted steels are not subject to stress corrosion cracking
I
I
cryogenic uses characterize stainless steels wedging action of solid corrosion products (70A) which may occur during stress corrosion attack can be critical if the products are insoluble, occupy a larger volume than the metal from which they are formed, and form in a critical area such as notches or cracks. Special processing methods such as vacuum melting may be practical for chemical applications. For example, a vacuum treated stainless steel is shown to be immune from stress corrosion cracking, but another of the same composition, except that it contained molybdenum, is not (72A). I n this connection the influence of both vacuum melting and the presence of different additives in stainless alloys has been investigated ( 7 A ) . Another investigator changed the environment and successfully avoided stress corrosion cracking. Cracking by chlorides in normal cleaning solutions has been avoided, using sulfamic acid ( 5 A ) . Intergranular corrosion continues to warrant mention. Experience with niobium-bearing austenitic stainless steels (AIS1 Type 347) indicates that the normal composition
W. A.
J . H. P E A C O C K
does not ensure immunity in the sensitized condition. Several modifications of this alloy at varying niobium-to-carbon ratios were tested to explain the variance ( 6 A ) . I t was found that in addition to carbon, nitrogen is also critical in determining the amount of niobium needed for stabilization. T h e minimum is:
yoniobium
= 8 X
LUCE
Yo carbon + yo nitrogen
3.3 X
I n the behavior of austenitic stainless steels in nitric acid solutions containing hexavalent chromium, silicon also is important. Corrosion resistance increases with an increase in silicon content, and intergranular attack ceased at contents higher than 2% (44). Silicon seems to strengthen the passive film, increasing corrosion resistance. Industrial Applications
Chemical. An excellent article
(7B) provides tabular information on the corrosion resistance and mechanical properties of stainless steels used in chemical applications. Nitric acid, s t i P an important corrosive, has gained in importance
because of its use as a rocket fuel. Fuming nitric acid is extremely corrosive even to the austenitic stainless steels, and great care must be exercised not only in selecting the most suitable grade but also in fabrication details and operating conditions. A few years ago a serious valve failure occurred on a fuming nitric acid storage tank. The discharge line on the west side of the tank was heated to an abnormally high temperature during summer afternoons and this resulted in the failure of 18 Cr-8 Ni valve parts that were acceptable in other locations. Such situations are extremely difficult to predict but an adequate factor of safety should be provided. A practical acceptance test for welded stainless steel fabrications handling fuming nitric acid is suggested ( 6 B ) . A good correlation between degree of sensitization and carbon content of the base metal can be obtained to assure freedom from intergranular failures. The widespread use of liquid fertilizer has resulted in many corrosion problems. Test work completed by one group ( 4 B ) indicates VOL. 5 5
NO. 7
JULY 1963
51
'1
Use Modern WOOD TANKS WITH
1
these alloys also contain significant quantities of cobaltandmolybdenum. LITERATURE CITED
cornion
POLYMER
(1A) Acello, S. J., Greme, N. D., Conosion 18,28691 (August 1962). (ZA) Bamartt, S., Ibid., 18, 322t-30t (September 1962). (3A) Betti, A,, Cavallam, L., Trabanelli, G., Zuccbi, F., 162.. 18, j51t-38t (October 1962). (4A) Coriou, H., Desestret, A., G r d , L., Hochmann, J., Cmpf. Rend. 254, 4467-9 (June 25, 1962). (5A) Dana, A. W.,M s f d R4g. 81, 86-7 (April 1962). (6A) Helley, E. J., LittIe, A. T.,Derbyshire, D. E., J. Irm rmd S e d Inrl. 200, 943-5 (November 1962). (7A) Lang, F. S., CaTorion 18, 378t42t; (October 1962). (SA) Luce, W. A., Peacock, J. H., IND. ENO.h u . 54,63,64,67-9 (June 1962). (9A) Mueller, W. A,, Cararton 18, 73t-9t (February 1962). (1OA) Pick-g, H. W.,Beck, F. H., Fontma, M. G., mid., 18, 230t-9t (June 1962). (11A) Sehmidt, H. W.,Brouwer, A. A., M&n& Rdmtim 1, 26, 27-32 (Fcbruary 1962). (12A) Stickler. R., Bamartt, S., J. Elccfrocham. Sw. 1 0 9 , 3 4 M (April 1962).
No~-Corrwive Lbw liiliil Go11 L o r M i i n l a n a n o o Qwt Higb 11t i l i t i o n Value Eat). EreotirI
IndusPLI Applicatiom Chicago 16, Illinois
624 W. Cermak Road
(1B) h m i m Reucnrion ef Cow4 9,25-30 (February 1962). (2B) Maya, G., Balajiva, K., Mat0llurg.u 65,ll-17 (January 1962). (3B) Mefd Prop. 81, 158, 162, 164 ( M a d 1962). (4B) Sbder, T. F., heprint, Natl. Aaroe. conmion Engn., 18th Ann. 1962. (5B) Sbcpheard, R. G., Donacbic, M. J.. ASM Trmu. Qumfmly 55, 45-50 (March 1962). (6B) Vialam, M. M., Apert, C. E., Matmioh Rescmch OndSdmds 2,111-14 (February 1962). (7B) Watson, J. F., Christian, J. L., AIME Mdollwgicol Soc., Tronr. 224, 99&1005 (October 1962).
w.,
INANIC IN1
lTES
When you need an organic intenncdiats prepared by chlorination in commercial or laboratory quantities, Pfister Chemical Works is prepared to help you. We have central storage facilities for hulk chlorine and cin pipe it to various reaction vesscls. This allowa for rapid, economical preparationof your prodnct.
1
CI
0 \
m-
"z
1-prf ist er
(1C) Iron a d S t r r l 3 5 , 4 7 (February 1962).
Your inquiries about chlorinationor other syntheses arc invited. All inqn@a are treated confidentially and rcyve prompt attenbon. 2-amino5-chbro-toIuene is an exampIe of the intermediates which PfiNer Chemical Works pmduce~by CHLORINATION.
CllBlMICfAL IUdgejieId, WORKS, [IC. New Jersey
CirnlI I@. a IU*M' Sulk@ w
54
Alby Devehpmcnt
IN D u S T R IA L A N D E N G I N E E R I N G
' c nEMIST R Y
ACI App(i., ?vuUdIons 1155 SISI., N.W. W w h l q k a 6. D. C
viding a more homogeneous structure. This is particularly important in solutions whichhaveunusually high wetting characteristics and have a tendency to penetrate areas lacking in homogeneity. Also, advances in vacuum melting and pouring technology are promising for improving the quality of stainless steels. For vacuum melting, however, conversion of existing equipment is expensive, and such major changes require years. Contrary to previous thought, effects of neutron irradiation on metals and alloys can be beneficial rather than harmful. Certain properties can be greatly enhanced by irradiation and the austenitic and ferritic stainless steels are relatively consistent in their behavior. When searching for special properties in stainless steels and other alloys, a knowledge of changes caused by irradiation can be a definite asset. Manufacture and Fabrication
Many interesting and relatively new developments have occurred in manufacture and fabrication. In addition to the vacuum melting and pouring, such developments include vacuum heat treating, brazing, and welding; stretch forming a t subzero temperatures; hot machining; chemical milling ; high frequency spark machining ; explosive forming; election beam welding; and laser light beam welding. Some of these procedures have reached commercial practice but others remain primarily in research and development. In terms of metal working techniques, exotic metals and alloys for space age and related equipment have been most prominent. Nevertheless in the long range the chemical process industry will probably benefit from these developments, and it is significant that stainless steels have been included in many of the studies. At present, many of these processes are costly, but as the scope broadens and technology advances economic aspects will become more favorable. T h e chemical process industry would weIcome any advance that will minimize corrosion and mechanical failure.
Miscellaneous Iron-Base Alloys
Iron-base alloys meriting attention are the austenitic nickel cast irons, 9% nickel steel, and the maraging nickel steels. Though none are known strictly for corrosion resistance, mechanical properties and economy indicate their use. The flake graphite austenitic nickel cast irons have certain mechanical limitations even though they are used in equipment such as pumps, valves, piping, and vessels. All of the advantages of these alloys are incorporated into the more recent development, ductile or spheroidal-graphite austenitic cast irons. I n addition to resistance against sea and brackish water, inorganic salts, alkalies, organic acids, and other media, they also have good castability, machinability, resistance to abrasion and galling, and satisfactory properties to elevated temperatures. By slightly modifying composition, one of these alloys becomes outstandingly tough and ductile below - 328 O F. T h e expanding cryogenic industry has greatly increased the use of 9% nickel steel, particularly because it is less expensive than stainless steel and yet has greater strength. Approval of Code Case 1308 by the A.S.M.E. Boiler and Pressure Vessel Committee in 1962 permits this alloy to be used without need of a post weld stress-relief treatment. Thus, vessels can be fabricated in the field without heat treating facilities limiting the vessel size. Operating temperature for welded pressurevesselsis -320Oto 150OF. The nickel maraging steels are of particular commercial interest because they can attain yield strengths in the magnitude of 250,000 to 300,000 p.s.i. and yet maintain exceptional toughness and ductility. Other characteristics include good resistance to stress corrosion in sea water, good formability without in-process anneals, low coefficient of expansion, freedom from decarburization, simple heat treating procedure, and good weldability without preheating. In addition to containing approximately 18% nickel, (Continued on page 54) Circle No. 24 on Readers' Service Card VOL. 5 5
NO. 7
JULY 1963
53
these alloys also contain significant quantities o f cobaltandmolybdenum. L I T E R A T U R E CITED Corrosion (1’4) Acello, S. J., Greene, N. D., Corrojiorz
Non-Corrosive Low I n i t i a l Cost L o w M a i n t e n a n c e Cost High Insulation Value * Easy Erection The introduction of N E W P O L Y M E R LININGS for W o o d Tanks has made possible the “POLYCEL” tank-for practically any a PH range chemical solution-covering from zero to fourteen. The combination of a low cost wood membrane and a variety of tough, resistant polymer films offers b i g advantages over high priced alloys.
18,286-91 (August 1962). (2A) Barnartt, S., Zbid., 18, 322t-30t (September 1962), (3A) Betti, A., Cavallaro, L., Trabanelli, G., Zucchi, F., Ibid., 18, 35lt-38t (October 1962). (4A) Coriou, H., Desestret, A , , Grall, L., Hochmann, J., Comfit. Rend. 254, 4467-9 (June 25, 1962). (5A) Dana, A. W., M e t a l Progr. 81, 86-7 (April 1962). (6A) Helley, E. J., Little, A. T., Derbyshire, D. E., J . Iron and Steel Inst. 200, 943-6 (November 1962). (7A) Lang, F. S., Corrosion 18, 378t-82t; (October 1962). (8A) Luce, W. A., Peacock, J. H., IND. ENG.CHEM.54, 63, 64, 67-9 (June 1962). (9A) Mueller, W. A., Corrosion 18, 73t-9t (February 1962). (10A) Pickering, H. W., Beck, F. H., Fontana, M. G., Ztid., 18, 230t-9t (June 1962). (11A) Schmidt, H. W., Brouwer, A. A , , Materials Protection 1, 26, 27-32 (February 1962). (12A) Stickler, R., Barnartt, S., J. Electrochem. Sac. 109, 343-4 (April 1962).
This 11,000 gallon P V C lined fir tank has been storing hydrolluorosilicic acid solution for years. A t mosphere in this refinery is very eorrosive. Steel hoops and lugs are covered with heavy polyethylene, Corrosion eliminated.
W r i t e for Bulletin 63 or see our literature in Chemical Engineering Catalog.
Industrial Applications
624 W. Cermak Road
Chicago 16, Illinois
Circle NO. 39 on Readers’ Service Card
When you need an organic intermediate prepared by chlorination in commercial or laboratory quantities, Pfister Chemical Works is prepared to help you. We have central storage facilities for bulk chlorine and can pipe it to various reaction vessels. This allows for rapid, economical preparation of your product.
(1B) Corrosion Preoention @ Control 9 , 25-30 (February 1962). (2B) Mayer, G., Balajiva, K., Metalluigia 65, 11-17 (January 1962). (3B) M e t a l Prop. 81, 158, 162, 164 (March 1962). (4B) Shaffer, T. F., Preprint, Natl. Assoc. Corrosion Engrs., 18th Ann. Conf., 1962. (5B) Shepheard, R. G., Donachie, M. J., A S M Trans. Quarterly 5 5 , 45-50 (March 1962). (6B) Vialatte, M. M., Apert, C. E., Materials Research and Standards 2, 111-1 4 (February 1962). (7B) Watson, J. F., Christian, J. L.: AZME Metallurgical Soc., Trans. 224, 998-1005 (October 1962). Alloy Development (1C) Iron and Steel 35, 47 (February 1962).
Your inquiries about chlorination or other syntheses are invited. All inquiries are treated confidentially and receive prompt attention.
2-amino-5-clzloro-toluene is an example of the intermediates which Pfister Chemical W o r k s produces by CHLORINATION.
STEELS FOR L O W TEMPERATURE
I&EC May, 1963, p a g e s 18 t o 29 Reprints a v a i l a b l e 0.75 Discounts-10 to 49 copies 15% 5 0 t o 99 copies 20% Prices for larger quantities u p o n r e q u e s t
CHENICAL WORKS,
REPRINT DEPARTMENT
IHG,
A C S A p p l i e d Publications 1 1 55 Sixteenth St., N.W. Washington 6, D. C.
Ridgefield, New Jersey Circle No. 29 on Readers’ Service Card
54
INDUSTRIAL A N D ENGINEERING CHEMISTRY
I
