THE ROLE OF STAINLESS STEELS IN PETROLEUM REFINING 1 TABLE OF CONTENTS INTRODUCTION Throughout the booklet these Petroleum refining today is unusually materials will be referred to as indicated Introduction ................................. 3 sophisticated in comparison to the above, without distinguishing in each Petroleum Refining ....................... 4 single shell stills of the 1800's, and instance into which category they Applications for Stainless Steels ... 6 the industry shows every indication of belong. Crude Distillation..................... 6 becoming even more complex. Every effort has been made to insure Fluid Catalytic Cracking .......... 9 Chemical and mechanical engineering that the applications described in this Delayed Coking ................... 13 advances are being sought to increase booklet reflect general industry practice Hydrotreating ...................... 16 product yields and improve plant and that the data are technically correct. Catalytic Reforming ............. 20 operating reliability. Methods are being However, neither the Committee of Hydrocracking ..................... 21 developed to remove potential Stainless Steel Producers nor the Hydrogen Plant .................... 23 pollutants from processes as well as companies represented on the Gas Plant ............................ 26 products. Changing national interests Committee warrant the accuracy of these Amine Plant.......................... 28 among oil-producing countries are data. Sulfuric Acid Alkylation ........ 30 affecting sources of raw crude supplies. The Committee of Stainless Steel Sour Water Strippers ........... 32 One result of these changes is a Producers acknowledges the help by Stainless Steels ......................... 34 growing emphasis on materials many companies and individuals Mechanical Properties ......... 35 engineering, and greater interest is contributing photographs and/or technical information, especially Ernest Types of Corrosion & being shown in the high-alloy, corrosion resistant steels, especially stainless Ehmke of Exxon Oil Company for his help High-Temperature Effects ... 38 in assembling the application data. Uniform Corrosion ............... 38 steels, to cope with a wide variety of Pitting ................................. 38 raw crudes. Crevice ............................... 38 Stainless steels are engineering Intergranular ........................ 38 materials with good corrosion resistance Stress-Corrosion Cracking ... 40 in environments containing various Cracking in Polythionic Acid 42 compounds of sulfur. They have high strength, excellent fabrication Naphthenic Acid .................. 44 characteristics, and can readily meet a Oxidation ............................. 47 wide range of design demands – load, Sulfidation ........................... 48 service life, low maintenance, etc. Embrittlement ...................... 52 The applications for stainless steels in Carburization ....................... 53 petroleum refining are many and varied. Hydrogen Attack .................. 53 The purpose of this booklet, therefore, is Cooling Water Types ................. 54 to help materials engineers identify Fresh Water ......................... 54 those applications and to provide data Polluted Fresh Water ........... 54 to support the use of stainless steels in Polluted Salt Water .............. 54 the high-temperature, corrosive Fresh Salt Water ................. 54 environments that may be encountered. Cooling Towers ................... 54 The stainless steels described in this References ................................ 56 booklet are the following AISI-numbered stainless steels and commercial proprietary alloys: Proprietary AISI Types Stainless Steels Photographs of the refinery appearing in this 405 20Cb-3 booklet were supplied by Marathon Oil 410 439 Company and Ralph M. Parsons Company, 430 216 the prime contractor. 440 410S 304 304L 18-2(FM) 309 309S 18-2 310 310S 26-1 316 316L 26-1 Ti 317 317L 18-18-2 321 A286 329 6X 330 Nitronic 50 Catalytic reformer section of Marathon Oil 347 29-4 Company Garyville Refinery showing Plat- former fired heaters. 29-4-2 18-18-Plus Photograph: Marathon Oil Company Ralph M. Parsons Company 3 TABLE 1 Corrosives Found in Many Refining Processes PETROLEUM REFINING Sulfur –present in raw crude, it causes high-tempera- A typical modern petroleum refinery ture sulfidation of metals, and it combines for the primary purpose of producing a with other elements to form aggressive com- complete range of domestic and pounds, such as various sulfides and sul- industrial fuels is illustrated by a block fates, sulfurous, polythionic, and sulfuric diagram in Figure 1. The refinery also acids. could supply several feedstocks for a Naphthenic Acid –a collective name for organic acids found pri- present day petrochemical plant and marily in crude oils from western United base stocks for lubricating oil States, certain Texas and Gulf Coast and a production. few Mid-East oils. Raw crude is separated by fractional distillation into petroleum gas, naphtha Polythionic Acid –sulfurous acids formed by the interaction of (gasoline), middle distillates (kerosene sulfides, moisture, and oxygen, and occuring and jet fuel), gas oils (cracking stocks), when equipment is shut down. lubricating oil cuts, and residual oils Chlorides –present in the form of salts (such as mag- used for fuel oils, asphalt, or thermal nesium chloride and calcium chloride) orig- crack stocks (coking). inating from crude oil, catalysts, and cooling All the streams from crude distillation water. are further processed or treated to convert the many fractionated materials Carbon Dioxide –occurs in steam reforming of hydrocarbon in to saleable or useful petrochemical hydrogen plants, and to some extent in cat- stocks. These processes involve the alytic cracking. CO combines with moisture 2 separation of gases and absorption or to form carbonic acid. removal of unwanted deleterious- Ammonia –nitrogen in feedstocks combines with hydro- polluting substances such as carbon gen to form ammonia-or ammonia is used for dioxide, ammonia and hydrogen sulfide. neutralization-which in turn may combine with Gasoline stocks, and mid-barrel other elements to form corrosive compounds, stocks are hydrogenated or such as ammonium chloride. hydrotreated to convert organic sulfur and nitrogen to hydrogen sulfide and Cyanides –usually generated in the cracking of high- ammonia for easy removal. Gasoline nitrogen feedstocks. When present, corrosion stocks are catalytically reformed to rates are likely to increase. improve knock rating and combustion Hydrogen Chloride –formed through hydrolysis of magnesium characteristics. chloride and calcium chloride, it is found in Heavier oils, gas oils and vacuum many overhead (vapor) streams. On conden- residuum are thermally cracked sation, it forms highly aggressive hydrochloric (pyrolysis-coking), catalytically cracked acid. (fluid catalytic cracking), or hydrogenated (hydrocracked) to Sulfuric Acid –used as a catalyst in alkylation plants and is increase yields of valuable products. formed in some process streams containing Olefins can be combined with an sulfur trioxide, water and oxygen. aromatic via an acid catalyst – Hydrogen –in itself not corrosive but can lead to blister- alkylation – to produce a branch chain ing and embrittlement of steel. Also, it readily hydrocarbon of high octane number. combines with other elements to produce Hydrogen requirements are met by a corrosive compounds. water gas reforming reaction between steam and methane over an active Phenols –found primarily in sour water strippers. catalyst at extremely high temperatures. Oxygen –originates in crude, aerated water, or packing Waste water is treated and hydrogen gland leaks. Oxygen in the air used with fuel sulfide is converted to sulfur. in furnace combustion and FCC regeneration Raw crude entering a refinery contains results in high-temperature environments several forms of sulfur, water, salts, which cause oxidation and scaling of metal organic nitrogen and organic acids surfaces of under-alloyed materials. which split, combine, or convert into numerous corrosive combinations. The Carbon –not corrosive but at high temperature results primary corrosives are indicated on in carburization that causes embrittlement or Figure 1 by being underlined and are reduced corrosion resistance in some alloys. briefly discussed in Table 1. 4 Figure 1 Petroleum Refinery 5 Figure 2 Crude Distillation APPLICATIONS Effluent from the heater, which at this pumped through a direct-fired heater to stage is a combined liquid and vapor the vacuum towers. At a temperature of Crude Distillation stream, is transferred to the atmospheric about 750-775F (399-413C), the heavy tower where the vapor is fractionated into vacuum gas oil and lube oil cuts are Figure 2 is a flow diagram of a typical a gasoline overhead product and four separated from the vacuum residuum crude distillation unit with one stage liquid sidestream products. Circulating and, using circulating reflux streams, of atmospheric distillation and two pumparound and overhead pumpback condensed in the tower. After further stages of vacuum distillation. The areas streams provide reflux. cooling, this vacuum gas oil is either sent in blue indicate locations for stainless After condensing, the overhead to storage or to other refinery units. The steel use, and the circled numbers refer gasoline fraction is pumped to a vacuum residuum is again heated and to process elements discussed