薄膜蒸发器筒节整体夹套封口环应力分析及其改进设计

1、薄膜蒸发器筒节整体夹套封口环应力分析及其改进设计刘友宏(清华大学胡国霖(中石化有限公司金陵分公司设计院摘 要 根据对流传热数值模拟结果, 建立了薄膜蒸发器筒节整体夹套结构的有限元计算模型, 利用有限单元法进行了结构的应力分析和强度计算。计算结果为:当不考虑温度载荷时, 结构是安全的; 当考虑温度载荷时, 结构肯定是欠安全的。对此又进行了改进结构设计和相应的强度计算, 并经受了实践的考验。关键词 薄膜蒸发器 筒节 夹套 应力分析 有关全夹套强度理论的研究, 国内外都做过较多的工作。对仅容器筒体部分包有夹套的整体夹套结构, 因为夹套内流体压力引起的封口环处的弯曲应力很小, 前人研究较少。本文研究的

2、多台按规范设计的18m 2薄膜蒸发器在使用5个月后仍然发生了容器最上面一段筒节的夹套封口环与筒体连接的焊缝热影响区大面积穿透裂纹。在排除了其他一些可能因素后, 笔者认为在夹套类传热结构设计中, 当容器筒体两侧介质温度差较大时, 还需考虑流固耦合作用, 进行包括固体壁面在内的流体力学、传热学计算。然后利用固体力学进行包括温度载荷在内的应力场的精确计算, 最后进行应力分析设计。按以上思路, 笔者进行了薄膜蒸发器夹套结构的流固耦合对流传热数值模拟, 在本文中建立了结构的有限元计算模型, 进行了原结构和改进设计结构的应力分析, 并按沿线进行强度评定方法进行了强度评定。1 有限元模型建立1 1 夹套结构

3、和温度场18m 薄膜蒸发器是一种直立容器, 主体分3段筒节, 每段结构相同, 其中的一段结构见图1。在夹套的中间位置有一个厚壁加强圈, 加强圈上有许多沿圆周方向均布的通孔, 以便导热油流过。容器的主要设计参数如表1所示。容器筒体内80, , , 2水系混合物溶液从筒体内壁面顶部降膜流下, 容器筒体外表面夹套中320 的导热油从夹套底部进入, 经与筒体外壁面换热后, 从夹套上部侧面出口离开。夹套结构对流传热数值模拟的计算域见图2, 计算出的夹套封口环处温度场见图3。图1 18m 薄膜蒸发器筒节结构简图表1 18m 2薄膜蒸发器主要设计参数设计参数设计压力/MPa设计温度/ 工作介质焊缝系数 腐蚀

4、裕度/mm主要受压元件材料容器类别设备内-0. 1200水系混合物溶液0. 851. 00Cr18Ni9夹 套0. 4320导热油0. 851. 016MnR2 计算中考虑的载荷:夹套内的筒体部分承受压力载荷为0. 5MPa; 夹套内的其他部分表面承受压力载荷0. 4MPa; 夹套外容器筒体的外表面承受0. 1MPa 压力载荷; 所有固体壁面中各节点的温度载荷按数值模拟结果输入。图2 温度场计算域示意图a. 原设计图3 夹套封口环处温度场等值线图1 2 网格划分因为容器具有轴对称性, 所以采用轴对称实体单元对图1的夹套结构进行网格划分。另外, 由于筒节结构在轴线方向具有1/2对称性, 同时使用

5、时夹套的上封口环最先泄漏, 所以取加强圈以上的半筒节为研究对象。经过网格划分试验和调整, 在充分保证计算精度的条件下, 划分的有限元网格如图4所示。容器筒体划分单元的最大长度为0 09(R T 1/2, 远小于(R T 1/2, 满足Mershon 准则1。对原设计划分的单元总数为849, 节点总数为1136。改进设计后划分的单元总数为1005, 节点总数为1344。1 图4 有限元网格划分图约束条件:在图4所示的有限元模型网格中, 由于加强圈的刚度很大, 并且处于对称面上, 所以此面上节点的轴向位移和转动自由度均为0。另外与上法兰连接的筒节各节点径向位移和转动自由度均为0。1 4 有限元计算

6、软件采用有成熟使用经验的通用有限元计算软件 ALGOR -FEA12有限元分析系统。2 有限元应力计算与改进设计根据上面建立的有限元计算模型, 分2种载荷工况进行了计算:在工况一下结构承受压力和温度的作用; 在工况二下结构仅承受压力作用。的应力强度场如图5所示, 结构中的最大应力点位于筒体与封口环连接的焊缝区, 其虚拟弹性最大应力强度已远远超过材料的屈服限, 必须进行强度评定。该焊缝区在工况二下的应力强度场如图6所示。从图5、6中可见, 压力载荷引起的应力是很小的, 而温度载荷引起的应力却非常大。工况一下最大应力点和工况二下同一点的各应力分量见表2 。图7 改进设计工况一下应力强度等值线图3

7、强度评定3 1 依据按照ASME 锅炉及压力容器规范第 卷第二册中AD -140设计准则的规定, 强度校核采用最大剪应力理论, 应力强度规定为最大剪应力的2倍, 即:S =max| 1- 2|, | 2- 3|, | 3- 1|式中 S 应力强度; 1、 2、 3 主应力。根据ASME 锅炉及压力容器规范第 卷第二册强制性附录4(以应力分析为基础的设计 中的规定:一次总体薄膜应力强度P m 应不超过设计许用应力强度S m , 即:P m S m一次局部薄膜应力强度P l 许用极限为1 5S m , 即:P l 1. 5S m一次局部薄膜应力加一次弯曲应力的应力强度P l +P b 的许用极限为

8、1. 5S m , 即:P l +P b 1. 5S m一次局部薄膜应力加一次弯曲应力以及二次应力的应力强度P l +P b +Q 的许用极限为3S m , 即:P l +P b +Q 3S m一次局部应力加二次应力以及峰值应力的应力强度P l +P b +Q +F 的许用应力幅为2S a , 即:P l +P b +Q +F 2S a式中 S a 容器材料在一定循环次数下的疲劳许用应力幅。薄膜蒸发器夹套加热结构在封口环固体壁内的应力类型有:总体一次薄膜应力P m 、局部一次薄膜应力P l 、二次应力Q 和峰值应力F 。从而对薄膜蒸发器中的最大应力点进行强度校核, 16MnR 在S 图5 原设

9、计工况一下应力强度等值线图图6 原设计工况二下应力强度等值线图表2 最大应力点的各应力分量值MPa原 设 计应力分量工况一11 22 33 12 23 31-2000. 37. 1-743. 027. 300工况二9. 6-0. 16. 62. 100工况一-435. 01. 6-166. 64. 400改进设计在改进设计中, 为了能有效降低温度载荷的作用, 夹套材料选用了热膨胀系数较小的碳素钢, 同时在夹套的中间增设了一个标准波形膨胀节(具体结构和尺寸参见L1300-6, JB1121-83 。改进设计的薄膜蒸发器在工况一下最大应力点附近的应力强度场如图7所示。结构中的最大应力点仍位于筒体与

10、封口环连接的焊缝区, 膨胀节中的应力水平较低。最大应力点的虚拟弹性最大应力强度已超过材料的屈服限, 也必须进行强度评定。对比图5, 最大应力点附近的应力水平已有大幅度的降低, 最大应力点的各应力分量见表2 。3 2 结构的应力强度计算与评定为了从有限元分析结果中得到薄膜、弯曲和峰值等各类应力强度, 本文采用沿线进行强度评定方法进行计算2。首先在截面上过最大应力点沿壁厚方向确定一条应力处理线A -A , 如图4所示。沿该线建立一局部坐标系 , 为便于处理, 在应力为最大值的一端 =1, 另一端 =0。然后, 根据静力等效和静力矩等效原理, 分离出各类应力分量, 进行强度计算, 计算结果如表3所示

11、, 其应力处理 线A -A 原设计工况一改进设计工况二中计算步骤见图8。表3 薄膜蒸发器夹套结构有限元分析应力处理结果局部一次膜应力强度S = 1m - 3m 355. 71. 5S m 49. 01. 5S m一次加二次应力强度S = 1m +b - 3m+b2009. 2 3S m 393. 43S m峰值应力强 度S = 1F - 3F 2075. 4 3S m 416. 03S m图8 各类应力分量强度计算步骤4 结论4 1 仅按压力载荷引起的应力场进行强度计算, 原设计结构是相当安全的。4 2 温度应力的附加作用是导致薄膜蒸发器筒体与夹套的封口环处焊缝穿透裂纹、泄漏的主要原因。4 3

12、 在薄膜蒸发器夹套上增加膨胀节后, 结构是安全的。4 4 当夹套加热容器筒体两侧的温度差较大时,设计中应进行固体壁中的温度场计算, 然后进行分析设计。参 考 文 献1 Mershon J L. Nozzles and B ranch Pipes in Cylindrical Shells -Comparison of Experimen tal and Analytical M ethods forElastic Analysis Under Internal Pressure and External Mo -ment. WRC Bulletin in preparation, 19942

13、李永生, 沈迅伟, 於孝春. 受压圆筒矩形大开孔的三维有限元分析与强度评定. 压力容器, 1996, 13(4 :4450(收稿日期:2000-11-16, 修回日期:2001-02-20sults of heat ex changers wi th various flow patterns was made. Key Words:Heat Exchanger , Foul, Heat Transfer Perfor -manceStress analysis of the integrate jacket seal ring of the cyli nder of a thi n film

14、 evaporator and its im provem ent de -sign. Liu Youhong(Qinghua University, Beiji ng , China Hu Guolin (Desi gn Ins titute, Jinling Division, Sinopec, Nanjing, Jiangsu, China (147Based on the numerical simulation resul t of convective heat transfer , the finite element calculating model of the integ

15、rate jack -et structure of the cylinder of a thin fil m evaporator was estab -li shed, the stress analysis and the intensi ty calculation of the structure were made usi ng the finite element method. The result shows that the structure was safe when the temperature load was not in consideration; the

16、structure was not safe when the temper -ature load was in consideration. The structure design was im -proved, and the corresp onding intensity calculation was made, they were successful in practice.Key Words:Thin Film Evaporator, Cylinder, Jacket, Stress AnalysisStructure design of two -stage petroc

17、hem ical flow pum ps and their application. Zhao Wanyong(Gansu University of Technology, Lanzhou, Gansu, China (151The various s tructures of the centrifugal petrochemical flow pumps were compared, the important action of adop ting the dou -ble -extracting i mpellers and the double -turbine pressure

18、 chambers for i ncreasing erosion performance and balancing radial force was described . The theoretical analysis, test result, and commercial application show that the vibration of the pumps could be re -duced, the efficiency of the pumps could be increased, the hi gh efficiency zone could be exten

19、ded by using the small blade exit angle 2, the impellers with less blade number Z and large blade wrap angle , and two middle transition channels with X -shaped distribution.Key Words :Chemical Flow Pu mp, Structure Desi gn Simple criterion of the equivalent area rei nforcement of the openings of pr

20、essure vessels. Deng Xiaoming(Guangdon g Petrochemical College, Maomi ng , Guangdong, China (153Based on the compensation principle of equivalent area of the openings of pressure vessels and the design formulae regulated in National Standards , a simple criterion of opening reinforcement was derived

21、. The simplici ty and reliability of the formula were described, the function of applying the si mple cri terion to simpl-ifying calculation process was also described.Key Words:Pressure Vessel, Opening, Reinforcement, Cr-iterionFailure analysis of the jacket tubes of a cooli ng effluent steam heate

22、r. Chen Guofeng(Ethylene Plant, Guangzhou Petro -chemical Complex, Guangzhou, Guangdong, Chi na (155The failure cause of the jacket tubes of a cooling effluentsteam heater was analyzed, the result shows that the major cause was stress corrosi on, and some i mprovements were proposed.Key Words:Stress

23、 Corrosion, Jacket Tube of Heater, Fai-lure AnalysisCrack failure analysis of cylinder dryers. Lin Ping, Yue Bin, Li Changx i, Liao Dongtai, Ma Pengju(Res. Inst of Chem. Mach, Lanzhou, Gansu, China (157A macro -analysis and a micro -analysis was made for the weld seam cracks on the cylinder dryers i

24、n a compound fertilizer plant, and it was found out that the cause was stress corrosion crackin g , and some repair methods were proposed.Key Words:Stress Corrosion Cracking, Dryer Rettofit of the piston rings of 3D22( tpye nitrogen -hydrogen compressors. Yan Kezhong , Yang Yingjie (Shanxi Coki ng G

25、roup Co Ltd,Hongdong, Shanxi, China (160The cas t iron piston rings in the second section of 3D22( type compressors were changed into the packed MC nylon piston rings in a retrorit, the s tructure calculation of the packed MC nylon piston rings and their retrofit result were presented. The cast iron

26、 piston ri ngs in the first section and the third section were also retrofitted based on the experience above mentioned.Key Words:Ni trogen -Hydrogen Compressor, Piston Ring Non -preheating weld between 15CrMoR s teel and A3R steel. Liu Lanju(Shengli Refinery, Qilu Petrochemical Ind us try Corporati

27、on, Zibo, Shandong, China (162The non -preheating weld process between 15CrMoR heat re -sistant steel and A3R low carbon steel was presented.Key Words:15CrMoR Steel, A3R Steel, Weld, Preheating Application of the compensation pri nciple of wall thick -ness in the process of bending R /D 2tubes. Hou X-i aofen g , Sha Quanshu, Zhan g Yong , Zhang Xuefeng (Daqing Petrochemical Machinery Plant, Daqing, Heilongjiang, China(164 The application of the compensa