Pretreatments of stainless steels

Allen and Alsalim 22 compared the effect of various pretreatments of stainless steel (martensitic structure) on the torsional shear strength of napkin ring joints formed with an epoxy adhesive (Redux 319 (Bonded Structures Ltd.)). They concluded that... 

Pretreatment of Stainless Steel Reactor. Since quartz is unsuitable for fabricating an industrial reactor, we tested stainless steel (SUS 27) reactors. One of these was treated with 30% phosphoric acid solution for 12 hours at room temperature and then washed thoroughly (Reactor VII) and other was untreated and unaged (Reactor VI). Oxidations were carried out at 430°C. with a propane/oxygen mole ratio of 3 and at various flow rates. 

Pretreatments of Stainless Steels - Crevice Corrosion and High Temperature Oxidation (AES)... 

Surface pretreatment of stainless steel Joint strength (MPa) Locus of failure... 

The effect of storage at 100% RH at 21°C on stainless steel butt tensile/ structural epoxide adhesive joints is shown in Fig. 3. AAMS, GPMS and MPS were examined as pretreatments and the choice of stainless steel as the substrate... 

The amount of acid used per ton of stainless steel varies widely, depending on the surface area per unit weight, the temperature of the treated surface, the pretreatment conditions (annealing and rolling temperatures) and the grade of the stainless steel. Industry estimates vary widely, ranging from about 5 to 50 pounds of nitric acid consumed per tome of stainless steel produced. 

Experimental Apparatus and Procedures. The amorphous alloys of about 15 microns thick and 3 mm wide ribbons were prepared by the disk method (8), the details of which have been described elsewhere (5). The important step of the method is the impinging of the molten mother alloy, held in a quartz tube with a small nozzle, onto the surface of a rotating disk of stainless steel. A flow type of a reactor apparatus, previously described (5), was used for the catalytic reaction. The reaction was carried out under atmospheric pressure and at temperatures from 220 to 370°C. The catalysts were pretreated with a stream of hydrogen in advance of a run. A gas chromatography was used for analyzing the hydrocarbons methane, ethylene, ethane, propylene, propane, butenes, butanes, total C5 hydrocarbons, and higher hydrocarbons (C6 to Cj0, not separated), as well as carbon monoxide, carbon dioxide and water. Alcohols and aldehydes could be detected by the gas chro-motography but were not found to be produced in sizable amounts. 

Prevention of General Corrosion. Proper selection of materials. In design, a metal or alloy that forms a stable passive film should be recommended. A surface pretreatment in oxidized solutions has been adopted for stainless steels and is recommended in many circumstances. The most popular process a 300 min immersion in a 20 vol% nitric acid at 50°C is recommended for some types of stainless steels.21 The environment can be modified in the bulk and should be effective at the interface in adding oxidizing agents, such as nitrite or strong nitric acid, that maintain the passive state on some metals and alloys.8... 

The acidity of pyrolytic fluids is due primarily to carboxylic acids. Corrosion of pretreated 304 stainless steel at pyrolytic oil pumping temperatures, 130-140°F, has been measured at 0.05 to 0.10 mils per year. Corrosion rates are substantially reduced by emulsificalation of municipal solid waste oil with No. 6 fuel oil. 

The inertness of stainless steel columns matches that of fused silica and is derived from a multistep process which utilizes a multilayer pretreatment of the inner surface of the stainless steel. Each layer is chemically stable at elevated temperatures and has the same or higher mechanical properties as the steel tubing. The layers are chemically bonded together. Stationary phases are easily bonded to this stable inert surface, resulting in high-performance columns. 

The correct pretreatment, therefore, is vital and, amongst other considerations, it will be dependent on the grade of stainless steel being used as well as the minimum specified tensile strength of the substrate and the projected end use of the bonded component. 

Alkaline permanganate pretreatment of steel for the removal of heat scale and smut prior to acid pickling results in faster descaling and reduced metal attack (see Metal surface treatments Metal treatments). Stainless steel alloys can also be cleaned by alkaline permanganate followed by pickling in nonoxidi2ing acids (260). 

In addition, the magnetic characteristics of a material can change as a function of stress (e.g., unannealed series 316 stainless steel can be magnetic after machining), temperature, pressure, and physical and chemical treatment. Therefore, when two paramagnetic materials with similar magnetic susceptibilities are to be separated, the possibility that pretreatment will facilitate subsequent separation should be studied. 

Catalyst samples were pressed as a wafer in the stainless steel or perspex sample holder. It was calculated that, due to diffusion limitations, the aqueous samples needed at least 6 hours pretreatment in order to attain monolayer coverage of the platinum with oxygen or hydrogen throughout the sample. A pretreatment time of 20 hours was chosen. 

Temperature-programmed reaction (TPR) studies of partial oxidation of propylene was carried out by flowing CsHe (Praxair), O2 (Praxair), H2 (Praxair) and Ar (Praxair) through DRIFTS and stainless steel tubular reactor (3/8 OD) loaded with catalyst. Feed gas at 40 mFmin and 1 atm consists of C3H6 (10%), O2 (10%), H2 (10%) and Ar (70%) for temperature program reaction studies. Prior to each experiment, the catalyst was pretreated in H2 (10 vol%) and O2 (10 vol%) simultaneously at 250°C. Temperature was monitored with a K type thermocouple connected to an omega temperature controller. 

Most industrial reactors and high pressure laboratory equipment are built using metal alloys. Some of these same metals have been shown to be effective catalysts for a variety of organic reactions. In an effort to establish the influence of metal surfaces on the transesterification reactions of TGs, Suppes et collected data on the catalytic activity of two metals (nickel, palladium) and two alloys (cast iron and stainless steel) for the transesterification of soybean oil with methanol. These authors found that the nature of the reactor s surface does play a role in reaction performance. Even though all metallic materials were tested without pretreatment, they showed substantial activity at conditions normally used to study transesterification reactions with solid catalysts. Nickel and palladium were particularly reactive, with nickel showing the highest activity. The authors concluded that academic studies on transesterification reactions must be conducted with reactor vessels where there is no metallic surface exposed. Otherwise, results about catalyst reactivity could be misleading. 

A summary of some of the more common metal pretreatments is given by Derjaguin25). The literature also describes many specialized pretreatments for steel 26-29>, stainless steel 22,30), aluminum 23,31 35 copper 36 41) and other metals... 

Effect of Propane to Oxygen Mole Ratio in Feed. Table IV gives the results for the propane and oxygen mole ratio ranging from 2 to 8. Stainless steel Reactor VII was used for these experiments after the phosphoric acid pretreatment the reaction temperature was 430°C. The product gas was cooled in the Liebig condenser at 2°C., and the condensate was analyzed. 

For the synthesis, diffusion limitation occurred rather than crystal formation limitation. Stirring resulted in more uniform, but thinner coatings. Pretreatment of the stainless-steel support with dilute template solution improved the crystal growth in the upper part of the channels. 

The selectivity of amperometric detection has been useful in simplifying the sample pretreatment steps in the determination of a number of drug products [82-86]. A method requiring no sample preparation using an amperometric detector and UV detector in series was developed for lido-caine hydrochloride injectable solutions [87]. The drug epinephrine is quantified with the amperometric detector, whereas lidocaine and methyl para-ben are detected by ultraviolet light. Disodium EDTA had to be added to the mobile phase to eliminate a peak response from iron leached from the stainless steel. 

The Frank and Demint [200] method is directly applicable to water samples. After addition of sodium chloride (340g IT1) and aqueous hydrochloric acid (1 1) to bring the pH to 1, the sample was extracted with ethyl ether and the organic layer was then extracted with 0.1M sodium bicarbonate (saturated with sodium chloride and adjusted with sodium hydroxide to pH8). The aqueous solution adjusted to pHl with hydrochloric acid was extracted with ether and after evaporation of the ether to a small volume, Dalapon was esterified at room temperature by addition of diazomethane (0.5% solution in ether) and then applied to a stainless steel column (1.5m/3mm) packed with Chromosorb P (60-80 mesh) pretreated with hexamethyldisilazane and then coated with 10% FFAP. The column was operated at 140°C, with nitrogen carrier gas (30mL muT1) and electron capture detection. The recovery of Dalapon ranged from 91 to 100% the limit of detection was O.lng. Herbicides of the phenoxyacetic acid type did not interfere trichloroacetic acid could be determined simultaneously with Dalapon. 

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