Selection of Corrosion Resistant Construction Materials for Caustic Soda Production Equipment

Изготовление оборудования для упаривания щелочи натрия на сегодняшний момент требует ответственного подхода к выбору материалов, поскольку повышенная агресивность концентированных растворов вызывает некоторые сложности во время произвоства. В статье рассмотрена коррозионная стойкость отечественных и зарубежных материалов, как основного металла, так и сварных соединений в средах концентрирования электролитических щелоков в интервале концентраций NaOH от 12% до 99.5% и температуры от 115 до 395оС. Для испытаний из исследуемого материала изготавливались образцы размером 20×80 мм с поперечным сварным швами с двумя просверленными отверстиями. шлифовались и собирались в кассеты с помощью стержней из никелевого сплава. Впервые получены сравнительные данные по коррозионному состоянию конструкционных материалов при упаривании электролитических щелоков, полученных диафрагменным электролизом и электролизом с использованием ртутного катода. Результаты коррозионных исследований достаточно хорошо корректируются с опытом эксплуатации никелевых труб на первой стадии концентрирования щелочи. Оценена электрохимическая гетерогенность сварных соединений сплавов 33 и 201, изготовляемых фирмой «Крупп ВДМ». Проведенные исследования коррозионной стойкости сплавов 201 и 33 в условиях упаривания NaOH, полученного ртутным электролизом, подтвердили высокую коррозионную стойкость никелевого сплава 201 на основных стадиях концентрирования щелочи. Результаты исследования могут использоваться в качестве рекомендаций при разработке конструкционных материалов. The manufacture of equipment for the evaporation of sodium alkali at the moment requires a responsible approach to the choice of materials, since the increased aggressiveness of concentrated solutions causes some difficulties during production. The article considers the corrosion resistance of domestic and foreign materials, both the base metal and welded joints in the media of concentration of electrolytic alkalis in the range of NaOH concentrations from 12% to 99.5% and temperatures from 115 to 395оС. For testing, specimens of 20×80 mm in size with transverse welds with two drilled holes were made from the material under study. polished and assembled into cassettes using nickel alloy rods. For the first time, comparative data on the corrosion state of structural materials during evaporation of electrolytic slits obtained by diaphragm electrolysis and electrolysis using a mercury cathode were obtained. The results of corrosion studies are quite well corrected with the experience of operating nickel pipes at the first stage of alkali concentration. The electrochemical heterogeneity of welded joints of alloys 33 and 201 manufactured by “Krupp VDM” was evaluated. The conducted studies of the corrosion resistance of alloys 201 and 33 under conditions of evaporation of NaOH obtained by mercury electrolysis confirmed the high corrosion resistance of nickel alloy 201 at the main stages of alkali concentration. The research results can be used as recommendations for the development of structural materials.

Selection of Corrosion Resistant Construction Materials for Caustic Soda Production Equipment

The article considers the corrosion resistance of domestic and foreign materials, both the base metal and welded joints in the media of concentration of electrolytic alkalis in the range of NaOH concentrations from 12% to 99.5% and temperatures from 115 to 395°С. For testing, specimens of 2080 mm in size with transverse welds with two drilled holes were made from the material under study. polished and assembled into cassettes using nickel alloy rods. For the first time, comparative data on the corrosion state of structural materials during evaporation of electrolytic slits obtained by diaphragm electrolysis and electrolysis using a mercury cathode were obtained. The results of corrosion studies are quite well corrected with the experience of operating nickel pipes at the first stage of alkali concentration. The electrochemical heterogeneity of welded joints of alloys 33 and 201 was evaluated. The conducted studies of the corrosion resistance of alloys 201 and 33 under conditions of evaporation of NaOH obtained by mercury electrolysis confirmed the high corrosion resistance of nickel alloy 201 at the main stages of alkali concentration. The research results can be used as recommendations for the development of structural materials.

Experimental Investigations on ThermoMechanical Tensioning (TMT), comparison with Heat Sink, and Its Application to a Grillage Structure

Thin plates, which are widely used in ship structures, undergo weld-induced buckling distortions because of their lower critical buckling strength. Thus, there is a need for an active in-process distortion control mechanism in the welding involving thin plates. In this regard, a ThermoMechanical Tensioning (TMT) method was developed and implemented successfully. In the current work, experimental investigation of the effect of TMT pull on the resulting welding distortions is studied and also the TMT process is compared with a heat sinking technique. The experimental results indicate that an increase in the TMT pull would reduce the extent of weld-induced buckling distortions. The results also suggest that a complicated heat sinking technique can be effectively replaced by a TMT process in reducing the welding out-of-plane distortions. The concept of TMT is further extended to the fabrication of grillage structures used in ship structures, which includes longitudinal and transverse welds.

BEHAVIORS OF SLIP-CRITICAL BOLTS IN COMBINATION WITH FILLET WELDS

According to the Specification for Structural Steel Buildings (AISC 2010), slip-critical bolts can only share load with longitudinal welds in a joint. Moreover, the bolt available strength shall not be taken greater than 50% of the bearing-type. This paper presents the result of a series of joint tests verifying the specification. The joints were tested in a manner similar to previous work (e.g. Manuel and Kulak 2000). The slip strength values of JIS F10T and F14T bolts were tested and compared. Transverse and longitudinal fillet welds with a leg size of 12 mm and the same amount of weld material were adopted and tested respectively. The strength ratio between bolts and welds changes from 5/8 to 6/9 in the combination joints. The result shows that in the combination with longitudinal welds, the bolts tend to slip and contact the plates, developing greater bearing strength. In the combination with transverse welds, the bolts slip and the pretension decreases greatly. But the combination also causes the fracture surfaces of transverse welds to change, providing additional strength to compensate the decrease in bolt slip strength. The combination joints therefore can develop strength greater than the sum of slip strength and fracture strength.

Residual Stress Effects on Crack Growth in Nugget of Al-Li Alloy 2195-T8 Friction Stir Welded Joints

In this work, Compact-Tension (C(T)) specimens with transverse welds in the sample centre were designed. The residual stress distributions were measured parallel and perpendicular to the weld nugget. Fatigue crack growth (FCG) rates were measured in the lab air. It is shown that compressive residual stresses around notch have significant effect on FCG rates and the effect deceases with crack growing. FCG rate is lower in the nugget than in parent material. Effects of residual stress were studied with crack growing. The lower crack growth rate in nugget is believed to be linked in part to compressive residual stress, but also in part to a microstructure effect present when crack grows in the recrystallized nugget.

Repair Technology for Single Deck Distortion of Floating Roof Tank

The repair welding procedure and assembly method that is considered as the key of repair single deck distortion are pointed out in this paper. Also presented is the repair plan of single deck distortion which consists of four stages: stress release, distortion repair, stress adjusting, and sequential assembly. The steps and technical requirements of repair single deck distortion are as follows: Step 1: Installing repairing platform — The platform should have enough stiffness, or else it will influence the repair effect of single deck distortion. Step 2: Inspecting the stress and distortion of single deck plates — The intention of inspecting the stress and distortion of single deck plates is in order to select the welds which should be retained or removed, and to confirm the sequence of removing the welds. The method of lattice is applied in inspection. Step 3: Removing single deck plates — The principle of removing single deck plates is to remove longitudinal welds and adjust the longitudinal distortion of single deck plates first, then removing transverse welds and adjust the transverse distortion of single deck plates. Step 4: Eliminating the local stress of single deck — The key of eliminating local stress of single deck is to control the skill of releveling the single deck plates, assembly of shaped single deck plates, dot welding of single deck plates and inspecting the distortion of the single deck plates. Step 5: Eliminating the integral stress of single deck — The single deck is divided into nine parts. Small distortion of single deck is eliminated first, then the serious distortion. Step 6: Adjusting the distortion of assembled single deck plates — Adjusting the distortion of assembled single deck is a very important process for single deck repair. The adjusting method is from integral to local and then from local to integral of single deck repeatedly. Step 7: Welding single deck plates — The step is to weld short welds first, then long welds. From the center to all sides of single deck, the method of skip welding is applied. Step 8: Nondestructive examination — All welds should be examined in accordance with relevant standards. This technology can eliminate 98% of single deck distortion, which can eliminate the sinking risk of floating roof. The technical requirements of construction process developed in this paper can also be used to instruct the construction of the new floating roof tank’s single deck. The construction process helps to reduce the initial distortion of single deck.