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).
Article from The Oil and Gas Journal discussing the application, creep stress, and performance of Calorized steel tubes in refinery services.
| Identifier | ExFiles\Box 150\1\ scan0099 | |
| Date | 28th March 1935 | |
| March 28, 1935 THE OIL AND GAS JOURNAL 129 Application of Calorized Tubes to Refinery Service (Continued from Page 45) heads and each tube given 30 passes with sharp bladed knockers. In the case of the plain mild steel tube chips were cut out of the tube wall giving the interior a gouged appearance. On the heavy duty Calorized tube the polish was somewhat reduced but there were no noticeable dents or cuts. Micrometer measurement of the Calorized tube wall at conclusion of the cleaner test evidenced no measureable wear. Officials of the refinery stated that the accelerated wear test was equivalent to four years of ordinary cleaning in service. Following this cleaner test specimens were cut from the Calorized tube and submitted to high temperature oxidation test which demonstrated that there had been no breakdown in the iron-aluminum surface alloy. It is possible, however, to ruin any tube by allowing the tube cleaners to run in one position for a period of time. It occasionally happens that an operator will leave the tool running for a considerable period while he tends to other business. Fig. 5—Creep-stress curves at 1200° F.{Mr Friese} Application of Creep Data In applying creep test data to the design of cracking still tubes it is necessary to examine two conditions—the normal operating temperature and the maximum temperature with excessive coking. Depending upon a variety of factors, principally the type of oil heated, the velocity and the heat input, the tube wall temperature of the tube will start at from 60 to 150° higher than the oil inside and will rise as a lining of coke collects and interferes with the adequate cooling of the tube wall by the oil. Taken from the start to the end of a run the average tube wall temperature may be something like 150° hotter than the oil. We have found the use of the Barlow formula: O.D. tube X pres. sq. in. / 2 = tube wall stress to give a satisfactory result in practice. This allows for some inequality of stress across the wall. One school of thought feels that very high stresses are produced by the difference of temperature inside and out. This is true initially but if the stress at the inside is much higher than at the outside, creep will be more rapid until the two have equalized. At these temperatures creep varies about as the third power of stress. It therefore seems apparent that one side of the tube cannot remain permanently more highly stressed than the other. When the tube cools off, however, the outside will be in tension, and the inside in compression when the internal pressure is removed. Practice seems to bear out this theory for the low alloy pearlitic steels which have high conductivity. In the case of austenitic steels, however, there seems to be evidence to the contrary. In that case, the temperature stresses involved would be four or five times greater in the pearlitic steels and may give trouble if the steel goes through a brittle range on cooling. In the preceding paragraph we have discussed the application of creep stress data to normal temperature design. Usually it will be found that the wall thickness contemplated will be amply strong for that condition. However, due to the fact that the creep strength of all metal falls off rapidly with increased temperature, a relatively short time at 100-200° F.{Mr Friese} above the normal temperature will cause rapid swelling. Usually it is not possible to design a strong enough tube to carry indefinitely at the abnormal maximum temperature which may be attained, but one should ascertain whether the tube selected can carry on for several hundred hours of abnormal operation. Let us take an example. A tube is to heat heavy oil to 1,000° F.{Mr Friese} with 20,000-30,000 B.t.u. heat input. Average wall temperature will not be over 1,200° F.{Mr Friese} Pressure about 500 pounds at point where oil is nearly up to temperature. Tube size: 2½-inch O.D. X ¼-inch wall. Stress = 2 X ¼-inch = 2,500 pounds per square inch Reference to the creep stress deter- mination Figure 5 shows that at 1,200° F.{Mr Friese}, only 4-6 per cent Chr. Moly., 1 per cent Moly. Calorized and "DM{D. Munro}" have the requisite creep strength to stay below the 1 per cent in 10,000-hour value. But the 4-6 per cent Chrome Moly. does not have sufficient oxidation resistance to maintain the section intact at that temperature, hence we come to the use of the Calorized "DM{D. Munro}" or 1 per cent Moly. Now let us examine the abnormal temperature condition. At 1,300° F.{Mr Friese}, Figure 6, under a load of 2,500 pounds per square inch. Fig. 6—Creep-stress curves at 1300° F.{Mr Friese} for indicated steels Calorized "DM{D. Munro}" creep ... .25%/1,000 hrs. Calorized 1 per cent Moly, creep ..................... .18%/1,000 hrs. Since several per cent total creep before removal is possible, this means that the Calorized tubes of "DM{D. Munro}" or 1 per cent Moly. could run thousands of hours at 1,300° F.{Mr Friese} The 0.50 per cent Moly., however, would not carry the stress at even 1,200° F.{Mr Friese} since its strength falls off rapidly above 1,100° F.{Mr Friese} With the small increase in cost and greater superiority of the 1 per cent Moly., and "DM{D. Munro}" steels it is believed that these only should be considered. Should the temperature rise to 1,400° F.{Mr Friese}, however, the life would be limited to several hundred hours. If the temperature does rise to 1,400° F.{Mr Friese} it will only be rarely and never for long so that both of these tubes could carry on for short intervals at that temperature. At 1,400° F.{Mr Friese} under this stress a plain steel tube would be scaled and bulged dangerously within 10-20 hours. Refinery Applications Calorized molybdenum and "DM{D. Munro}" tubes have not only added to the life of the tube and reduced the yearly maintenance cost in conventional cracking stills but have made possible higher temperature and pressure operations heretofore considered impossible except with the very expensive 18 chromium 8 nickel alloy. --- HEAVY DUTY CALORIZED STILL TUBES CALORIZED Seamless steel tubes render the refiner valuable service in cracking still equipment because of their immunity to the attack of agencies which result in rapid deterioration of plain steel tubing. The iron-aluminum alloy surface is entirely immune to oxidation up to maximum metal temperatures of 1500 degrees F.{Mr Friese} and is not attacked by high sulphur crude oil. In present-day Heavy Duty Calorizing the surface alloy is tough and thoroughly bonded to the steel, presenting great resistance to erosion and tube cleaner wear. (LOAD—2000 LBS. PER SQ. IN.) CREEP SPECIMENS TESTED AT 1400° F.{Mr Friese} UNCALORIZED SPECIMENS M.{Mr Moon / Mr Moore} S. †Fractured 90 Hr. Elongation 79.4% C-Mo. †Fractured 110 Hr. Elongation 45.7% D.{John DeLooze - Company Secretary} M.{Mr Moon / Mr Moore} †Fractured 230 Hr. Elongation 21.7% Cr.{Mr Cra???ster / Mr Chichester}-Mo. †Fractured 487 Hr. Elongation 40.1% CALORIZED SPECIMENS M.{Mr Moon / Mr Moore} S. Fractured 99.5 Hr. Elongation 41.2% C-Mo. Fractured 480 Hr. Elongation 15.0% D.{John DeLooze - Company Secretary} M.{Mr Moon / Mr Moore} Not Fractured 600 Hr. Elongation 6.4% 1 Mo. Not Fractured 600 Hr. Elongation 2.24% M.{Mr Moon / Mr Moore} S. = MILD STEEL C-MO = CARBON-MOLYBDENUM (0.50 MOLY.) 1 MO. = CARBON-MOLYBDENUM (1.0 MOLY) D.{John DeLooze - Company Secretary} M.{Mr Moon / Mr Moore} = TIMKEN D.{John DeLooze - Company Secretary} M.{Mr Moon / Mr Moore} STEEL Cr.{Mr Cra???ster / Mr Chichester}-Mo. = 4-6 PER CENT CHROMIUM PLUS 0.50 MOLY. †Partly caused by Reduction of Section by Scaling. Complete details in bulletin: "High Temperature Creep Values of Low Priced Alloy Still Tubes." THE CALORIZING COMPANY - PITTSBURGH, PA.{Mr Paterson} | ||