タイトル無し
スポンサーリンク
概要
- 論文の詳細を見る
About 70 catalyst tubes in 7 terrace-wall type steam reformers were used for the investigation of service damages. The metal temperatures of the tubes were estimated by analysis of microstructural changes of the tube material, HK 40, formed during the services.Two types of creep damages were observed: Longitudinal fissures in the base metals including the heat affected zones (HAZ) of the girth weld joints, and circumferential fissures in the girth weld metals as shown in Fig. 2.Fig. 3 shows some typical examples of the temperature profiles, distribution of damages and σ phase precipitated areas. The distribution of longitudinal fissure in Fig. 4 indicates that the maximum damage in the base metal occurs near the bottom of furnace where the metal temperature is maximum and that HAZs are the preferential occurrent sites of the fissures. On the other hand, the occurrence of circumferential fissures in the girth weld metals depends not on the location but on the metal temperature, that is, it is restricted in the areas in which the metal temperatures are below 830°C as shown in Fig. 5.Table 2 shows that macrostructure including equiaxed grains inside the tube has a good resistivity against the longitudinal creep damage.Fig. 6 shows that σ phase precipitates in the metal temperature range from 700 to 900°C and preferentially in the weld metal.Fig. 7 shows that all fissures occur after four years of service. Note that the fissures grow and the probability of their detection increases with service time.Fig. 9 shows a creep rupture strength of HK 40 against the leakage fracture of the catalyst tube, estimated by the actual operating performances of the tubes used up to just before leakage. Fig. 9 also suggests that the leakage strength is in accordance with the recommended allowable strength of API RP530 except at low temperatures (below about 850°C) and the strength by NRIM data is less than the leakage strength through all parameters.The following problems exist in the conventional design of the tube: 1) neglect of thermal stress, 2) neglect of the strength of unsound layer of the tube, 3) incompatibility of the equation for calculation of wall thickness of the tube and 4) unclearness of the long-term creep rupture strength of HK 40. Nevertheless, Fig. 9 suggests that the tube designed by the conventional method satisfies the expected service life, when the minimum rupture strength of API RP530 is adopted as the allowable stress of HK 40.The following four ideas for prolongation of life of the catalyst tubes are derived from the results studied here: 1) application of a longer tube to avoid the existence of welding joints in the area where the maximum damage occurs, 2) application of centrifugally cast tube including equiaxed grains inside the tube which has a high resistivity against the creep fissure, 3) application of the tube of certain chemical composition which controls the precipitation of σ phase, 4) application of a welding method which gives a macrostructure with good resistivity against the circumferential creep damage in the weld metal.
- 公益社団法人 石油学会の論文
公益社団法人 石油学会 | 論文
- 担持金属ルテニウム触媒によるレブリン酸メチルの液相水素化反応
- 各種バイオエタノールサンプル中の不純物分析
- 超臨界水ガス化におけるフェノールとベンゼンの分解経路
- ベータ型ゼオライトを触媒添加材として用いた重質油接触分解での多次元反応制御
- バイオディーゼル燃料生成における低価格植物油の脱酸処理の影響