From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
The properties and performance of Calorized steels under various test conditions including stress, temperature, and corrosion.
| Identifier | ExFiles\Box 150\1\ scan0098 | |
| Date | 28th March 1935 | |
| March 28, 1935 THE OIL AND GAS JOURNAL 45 possesses the greater strength; at 1,300° F.{Mr Friese}; DM{D. Munro} and the 1 per cent Moly. steels are approximately equal; while at 1,400° F.{Mr Friese}, the 1 per cent Moly. steel is somewhat superior. Stress-Rupture Tests In order to show more clearly the differences in the load-carrying ability of these various Calorized steels, specimens of each were subjected to identical loads at a given temperature and the tests continued until fracture of some of them was obtained. The load selected was based on the stresses which are encountered in certain commercial applications. Similar tests were also conducted on certain of the uncalorized specimens in order to determine the influence of Calorizing on the load-carrying ability. The tests were conducted in a vertical, electrical furnace and although the ends were packed with asbestos, a certain amount of air seeped into the furnace. Figure 3 shows results obtained at 1,400° F.{Mr Friese} under a stress of 2,000 pounds per square inch. These tests were conducted for a maximum of 600 hours, and during this period all of the uncalorized specimens fractured. The maximum time, 487 hours, was required by the 4-6 cr.{Mr Cra???ster / Mr Chichester} + Mo steel while the mild steel required the least, 59 hours. Two of the Calorized specimens, mild steel and 0.50 Moly., also fractured in 98.5 and 480 hours, respectively. The DM{D. Munro} elongated 6.4 per cent in the 600-hour period and as a result its Calorized coating was cracked. The 1 Moly. steel, however, only elongated 2.24 per cent during this time period and no cracks appeared in the Calorized coating. These findings, therefore, offer further support to the statement made above, that is, that from 5 to 6 per cent deformation is required to produce cracking of the Calorized layer. If the results from the uncalorized and Calorized specimens are compared it will become evident that Calorizing increased the load-carrying ability in all cases. It is believed that the improvement in load-carrying ability obtained by Calorizing can be largely attributed to the increased resistance to oxidation rather than to an actual increase in the strength of the Calorized specimen. Sufficient tests of this type are to be undertaken to enable the determination of complete stress-time for rupture curves for each of these materials at 1,300 and 1,400° F.{Mr Friese} This phase of the work is not as yet completed. Figure 4, however, does show a curve of this type for DM{D. Munro} steel at 1,400° F.{Mr Friese} This curve appears to be-come asymptotic to a stress slightly below 2,000 pounds per square inch. Tensile Properties Tensile tests were conducted on some of the Calorized specimens in order to determine the influence of this operation on the strength and ductility characteristics. For comparative purposes similar tests were also conducted in certain cases on the uncalorized materials. The results obtained are shown in Table 2. The results indicate the ductility to be somewhat lowered by the Calorizing operation and especially is this true with the reduction of area values. The decrease is not sufficiently pronounced, however, to classify these materials as brittle. For example, in the Calorized condition, the elongation ranges from 31.3 to 32 per cent and the reduction of area from 29.2 to 35.7 per cent. The strength characteristics are in general slightly increased by the Calorizing operation. Hardness Tests Another of the outstanding advantages of a Calorized surface, in addition to its resistance to corrosion and oxidation, is its high surface hardness which enables it to resist erosion and the action of the tube cleaners. Because of the thickness of the coating, the ordinary penetration type hardness tests do not give a true picture of the actual surface hardness. The most suitable for measuring the hardness has been found to be of the scratch type, such as the Bierbaum scratch hardness test. Specimens of five different Calorized steels were subjected to this type of test and the results obtained are given in Table 3. Hardness determinations were made at three different positions in the Calorized coating as well as in the ferrite of the base material. The sections chosen in the Calorized coating were near the outer edge, at the center, and near the junction of the Calorized coating and the base material. Values for the micro-hardness of the Calorized coating range from 300 to 800, while the corresponding values for the ferrite in the base material ranged from 150 to 200. The entire cross-section of the Calorized coating is, therefore, considerably harder than the ferrite in the base material. The results indicate the hardness of the Calorized coating to vary, depending upon the depth from the outer surface. In every case the section near the junction showed the minimum hardness and this would be approximately .040 inch from the outer surface. In certain cases the outer surface of the Calorized coating possesses the maximum hardness while in other cases the maximum hardness occurred at a point more near to the center of the coating. Oxidation Resistance To make use of the high creep strength of the newer alloy steels, it is necessary, however, to be sure that the section will remain intact during the life desired. In general those temperatures (1,100° and up) which necessitate a stronger tube than killed mild steel also cause rather rapid oxidation of the tube exterior. None of the low alloyed pearlitic steels have appreciable oxidation resistance at 1,200° F.{Mr Friese} The newer type of heavy duty Calorizing will protect any of these steels from scaling at continuous temperatures up to 1,500° F.{Mr Friese} and for short periods even as high as 1,700° F.{Mr Friese} In Table 4 is presented the oxidation resistance of a number of these materials both plain and Calorized. Sulphur Corrosion Resistance In handling corrosive stocks cracking still tubes frequently fail by corrosion from the inside. In Table 5 is given the comparative corrosion resistance of the various low alloy steels, plain and Calorized. We have not found any laboratory test which will exactly duplicate the finery corrosion. In pure hydrogen sulphide gas, the 4 to 6 per cent chrome steels are attacked more readily than in an actual cracking still. The problem of laboratory accelerated tests is further complicated by the fact that in refinery service any corrosion products formed are soon scoured off by the tube cleaners exposing fresh surface. It is at least apparent from these hydrogen sulphide tests that the Calorized steel is immune to corrosion from hydrogen sulphide up to 1,200° F.{Mr Friese}, and in any concentration, which fact is verified by refinery use. Erosion of Tubes While the heavy duty Calorized surface has ductility (5 per cent elongation), it is extremely hard and may even be used to scratch glass. Providing that the turbine cleaners of either the Star wheel type or drill head or “knockers” are kept moving—they do no more than remove the surface roughness. Recently, at a prominent mid-western refinery the following wear test was made: The cleaner was traversed through the tubes at the rate of 5 feet per minute. On the first test cutters of the mild head type with new cutter wheels were employed—a new, separate tool for the Calorized and plain steel tubes. Seventy passes were made then all cutter wheels were renewed and 30 additional passes taken. At the end of this test one-thirty-second inch was worn from the wall of the mild steel tube and the ground in front of the bench littered with particles of steel torn from the tube wall. The heavy duty Calorized tube showed no wear and took a nice polish under the action of the cleaner. Following this test both cleaners were equipped with Acorn or knocker type (Continued on Page 129) TABLE 1—CREEP CHARACTERISTICS OF CALORIZED STEELS AT INDICATED TEMPERATURES Material—, Temp. °F.{Mr Friese}, Stress for rate of creep of 1 per cent in designated time period, hours , , 100,000, 10,000, 1,000 Mild steel, 1,100, 1,050, 2,050, 4,100 0.50 Moly., 1,100, 2,700, 7,000, 15,000 DM{D. Munro}*, 1,200, 1,950, 3,950, 8,100 4-6 Cr.{Mr Cra???ster / Mr Chichester} + Mo*, 1,200, 900, 2,500, 5,250 0.50 Moly., 1,200, 470, 1,650, 3,250 1.00 Moly., 1,200, 1,100, 2,800, 6,200 DM{D. Munro}, 1,300, 700, 1,500, 3,900 0.50 Moly., 1,300, 210, 840, 1,900 1.00 Moly., 1,300, 840, 2,000, 4,800 DM{D. Munro}, 1,400, 250, 560, 1,100 1.0 Moly., 1,400, 380, 750, 1,475 *Uncalorized. TABLE 2—EFFECT OF CALORIZING ON THE TENSILE PROPERTIES AT ROOM TEMPERATURE Material and condition—, Tensile strength lbs./sq. in., Yield point lbs./sq. in., Elongation per cent in 2 in., Reduction of area per cent Carbon (K), Uncalorized, 60,000, 35,000, 40.5, 66.8 Carbon (K), Calorized, 65,000, 32,500, 32.0, 31.8 Carbon (O), Uncalorized, 49,700, 25,000, 46.0, 67.0 Carbon (O), Calorized, 52,500, 28,750, 31.3, 29.2 1.0 Moly., Calorized, 52,575, 32,500, 31.5, 35.7 K = Steel of the killed type. O = Steel of the open or rimmed type. TABLE 3—HARDNESS OF CALORIZED COATING— Material, Position in Calorized coating—, —Bierbaum hardness— Width of scratch Microns, Micro-hardness DM{D. Munro}, Near outside edge, 2.945, 610 , Center, 3.120, 550 , Near junction, 4.341, 350 , Ferrite in core, 7.111, 200 Bain, Near outside edge, 2.452, 650 , Center, 3.201, 525 , Near junction, 3.121, 500 , Ferrite in core, 7.371, 195 0.50 Moly., Near outside edge, 2.800, 800 , Center, 3.578, 400 , Near junction, 5.000, 150 , Ferrite in core, 7.371, 190 1.00 Moly., Near outside edge, 4.267, 550 , Center, 4.267, 550 , Near junction, 5.750, 200 , Ferrite in core, 8.400, 150 1015, Near outside edge, 4.800, 425 , Center, 4.316, 530 , Near junction, 5.160, 290 , Ferrite in core, 8.090, 160 TABLE 4—OXIDATION RESISTANCE 1,200° air gain in wgt. mg./sq. cm., total 1,000 hours 1,500° air gain in wgt. mg./sq. cm., total 48 hours Type of material—, Samples, Plain, CZ., Plain, CZ. 18-8 Tubing, 1, .Plain, 1.1, CZ., 1.0 , 2, 0.52, 1.0 4-6 per cent cr.{Mr Cra???ster / Mr Chichester}, 1, 17.5, 1.58, 80.3, 1.4 1 per cent Tungsten, 2, 1.40, 78.5, 1.6 4-6 per cent cr.{Mr Cra???ster / Mr Chichester}, 1, 36.6, 0.88, 117.8, 2.4 0.45-0.65 per cent Moly., 2, 0.71, 111.2, 1.7 4-6 per cent cr.{Mr Cra???ster / Mr Chichester}, 1, 39.5, 0.56, 126.3, 1.8 , 2, 0.71, 123.0, Loss Plain, 1, 70.8, 0.80, 134.2, 2.5 Low carb. steel, 2, 0.92, 128.0, 2.1 Carbon-Molybdenum, 1, 83.6, 0.99, 127.7, 1.8 0.50 per cent Molybdenum, 2, 0.94, 126.5, 2.9 NOTE—None of the Calorized samples showed attack by oxidation. The slight gain in weight on Calorized specimens results from formation of a protective surface film. TABLE 5—GAIN IN WEIGHT—MILLIGRAMS PER SQ. CM. Gain in wt. per mg./sq. cm. 24 hours—900° F.{Mr Friese} hydrogen sulphide (6% H2S pure) 24 hours—1,200° F.{Mr Friese} hydrogen sulphide (H2S pure) Type of material—, Samples, Plain, CZ., Plain, CZ. 18-8 Tubing, 1, 0.29, 0.036 Loss , 2, 0.42 4-6 per cent cr.{Mr Cra???ster / Mr Chichester}, 1, 0.57, 17.5, 1.58 1 per cent Tungsten, 2, 0.58, 1.40 4-6 per cent cr.{Mr Cra???ster / Mr Chichester}, 1, 0.65, 0.12 Loss, 36.6, 0.88 0.45-0.65 per cent Moly., 2, 0.68, 0.71 4-6 per cent cr.{Mr Cra???ster / Mr Chichester}, 1, 0.35, 0.02, 39.5, 0.56 , 2, 0.33, 0.71 Carbon-Molybdenum, 1, 1.76, 0.033, 0.50 per cent Molybdenum, 2, Plain low, 1, 1.02, 0.035 Loss, 70.8, 0.80 carbon steel, 2, 0.95, 0.92 NOTE—None of the Calorized samples showed attack either by oxidation or sulphur corrosion. The slight gain or loss in weight on Calorized specimens results from formation of a protective surface film. Fig. 4—Stress-time rupture curve at 1400° F.{Mr Friese} (Graph showing stress in 1000 pounds per sq. in. vs.{J. Vickers} time for rupture in hours, from 0 to 1400 hours. The curve starts at approximately 3.5 stress units at 0 hours and drops, becoming asymptotic around 2 stress units after 1000 hours.) | ||