Pressure Vessel Design against Wind and Seismic Load

Transcription

1 Available online at Procedia Engineering 00 (2013) Selected papers of Mechanical, Civil and Chemical Engineering tracks of the 4 th Nirma University International Conference on Engineering (NUiCONE 2013) Pressure Vessel Design against Wind and Seismic Load Mr. Jiger Modi a, Prof. S J Joshi b, Prof. D B Shah b a Engineer, Inox Industries b Mechanical Engg. Dept. Institute of Technology, Nirma University Abstract To consider Wind-Seismic Loading on to the pressure vessels, different countries have provided respective codes. These codes are developed for buildings type structure, though they are providing information for Pressure Vessel like structures. Sometimes in the customer specifications, many of the data are missing regarding wind-seismic condition for particular location. Hence, designer has to read the entire code to dig out the missing data. This process is a time consuming, so a compiled document of codes providing information for pressure vessels only is prepared. A modal analysis is performed for uniform as well as non-uniform pressure vessel to prepare the L/D vs. Frequency plot particularly for stripper type vessels. The manual calculation is validated with the FEA analysis for frequency. Skirts are mounted on the basering, anchored to the concrete. The basering with continuous top ring is designed by using Brownell & Young and Simplified approach. Apart from that, while utilising the a commercial software for base ring design, software gives notes and warnings in output file. Pressure vessels are subjected to different kinds of loads i.e. pressure load due to internal or external pressure, moment load due to moment generated from the wind or seismic load, compressive/tensile load due to the weight of the elements, ladders, platforms, insulations etc. Wind applies force to the tall vertical pressure vessel fixed at the base. The bending stress induced is minimum at the top and maximum at the base. Hence it can be considered as a loaded cantilever beam. The bending stress produces compressive load at the downwind side and tension on the upwind side. The effect of seismic force is somewhat similar to the wind load effect. The only difference is the distribution of loads. The justification for the same was prepared as a guideline. As the vessel is subjected to wind-seismic load, it is subjected to the combined stress. Hence, the combined stress analysis is done as per ASME Section-VIII, Div-1. The result is compared to FEA. The combined stress analysis of cone to shell junction is carried out as per ASME Section-VIII, Div-2. The results are compared with the commercial software. The main objective behind this was to find out bugs from the software Published by Elsevier Ltd. Selection and/or peer-review under responsibility of the Institute of Technology Nirma University, Ahmedabad. Keywords: Modal analysis, Stripper type vessel, Commercial software, base ring, ASME, combined stress. * Corresponding author. Tel.: ;. address: s.j.joshi@nirmauni.ac.in

2 Jigar Modi / S J Joshi / Procedia Engineering 00 (2013) INTRODUCTION Fig.1 Pressure vessel acts as a cantilever beam ASME Section-VIII is used to design the pressure vessels. ASME does give the information regarding wind-seismic load, but it does not provide the method to calculate the load. But, different countries have developed the building codes to consider the effects of wind and seismic load. Designer has to read the code and find out the appropriate factors applicable to pressure vessels only. 2. PROBLEM DEFINITION The problem with the industry is, after receipt of order if data regarding the wind-seismic is missing from the customer specification then, designer has to read whole code and find out the missing data. Now, this task is too much time consuming. To overcome this problem a compilation is required. 2.1 Objective Prepare guidelines for different codes. Calculation of wind-seismic loads for different countries and validate with commercial software output to find out bugs if exist. Development of excel sheet for the codes not supported by the commercial software. To prepare a plot of L/D vs. frequency for stripper vessels. To prepare justifications for notes and warning produced by commercial software for base ring design. Combined stress analysis as per ASME Section-VIII, Div-1. Combined stress analysis of cone to shell junction as per ASME Section-VIII, Div-2.

3 Jigar Modi / S J Joshi/ Procedia Engineering 00 (2013) Methodology Study of codes and projects specifications and prepared the guidelines. Manual calculation to calculate the frequency for uniform as well as non-uniform vessel. Outcome is compared with the FEA by carrying out modal analysis. L/D vs. f plot is prepared for stripper type vessel. Design methods to design the base ring are studied and justifications are made for the warnings and notes. Combined stress analysis as per ASME Section-VIII, Div-1 is done manually and validated with FEA. No bugs are found from the software for Div-1. Combined stress analysis of cone to shell junction as per ASME Section-VIII, Div-2 is carried out and found bugs from the software. 3. GUIDELINES PREPARED FOR CODES. Guidelines are prepared for the following codes. Sr. No Description 1 Guideline for Algerian code 2 Guideline for Australian code 3 Guideline for ASCE code 4 Guideline for British code 5 Guideline for European code 6 Guideline for Indian code 7 Guideline for Brazilian code 8 Guideline for Peruvian code 9 Guideline for UBC 10 Guideline for Russian code 4. MODAL ANALYSIS OF STRIPPER TYPE VESSEL 4.1 Model of a stripper vessel Fig. 2. Model of a Stripper Vessel

4 Jigar Modi / S J Joshi / Procedia Engineering 00 (2013) Comparison of Analytical result to Modal analysis Frequency equation used for Analytical method, Table.2. Comparison of first mode frequency, Frequency Analytical Ansys % Difference f1 (Hz) L/D vs. frequency plot for Stripper type vessel: Fig.3 L/D vs. Frequency plot 5. JUSTIFICATIONS FOR NOTES/ WARNING FOR BASERING DESIGN: While designing the basering with Brownell & Young Method, commercial software is producing following note (highlighted in box): Fig. 4 Note generated by Commercial Software

5 Jigar Modi / S J Joshi/ Procedia Engineering 00 (2013) It was found that for the governing condition, software uses the following equation in backhand calculation: When, calculated the tensile load from the above equation, if it comes negative than, a highlighted note as shown in Fig. 4 is generated. As the value came out negative, software asks for test weight to consider in to the equation. After considering the test weight, if the value of tensile force is coming out positive then, the Brownell & Young iterations are performed. While carrying out the iterations if the tensile load on steel is coming out negative throughout, the following note is displayed in the output file. 6. COMBINED STRESS ANALYSIS: 6.1. Combined stress analysis as per Div-1: Fig. 4 Vessel used for combined stress analysis

6 Jigar Modi / S J Joshi / Procedia Engineering 00 (2013) Results obtained from the static structural analysis carried out in Ansys are shown in Fig 6. Fig. 5 Von-Mises Stress plot Fig. 6 Von-Mises Stress plot

7 Jigar Modi / S J Joshi/ Procedia Engineering 00 (2013) Comparison of results: Element Analytical (MPa) Ansys (MPa) % Difference Skirt(C.S) Skirt(A.S) Shell Head CONCLUSIONS 1. The guidelines for the codes widely used at the industry for pressure vessel design against wind and seismic load are prepared and they found very much useful for industry. 2. Guideline for basering design is also prepared showing justifications. 3. An L/D vs. F plot is prepared for stripper type vessel to find out the frequency at the time of enquiry only. The frequency found from manual calculation is validated with the FEA. 4. The combined stress analysis is carried out manually and validated with the FEA. Close results are found. 5. Bugs are found from the software and sent to the company, which are accepted and corrected in the new revision of the software. 8. REFERENCES [1]. The American Society of Mechanical Engineers, Section-VIII, Div-1 & 2. [2]. Moss, D. R., Pressure Vessel Design Manual, 3rd edition, Gulf Professional Publishing. [3]. Bednar, H. H., Pressure Vessel Design Handbook, Van Nostrand Reinhold Co, [4]. Brownell, L. E. and Young, E. H., Process Equipment Design, Vessel Design, John Willy and Sons Publishing. [5]. Freese, C. E., Vibration of Vertical Pressure Vessels, Journal of Engineering for Industry, February 1959.