Thermoplastic Scrubber Jaroslav Prazan Podlomní 4 636 00 Brno Czech republic Tel.: +420 548539654 Fax: +420 548539654 Contact: Prazan Jaroslav Email: [email protected] Activities The company is involved in the complex design and engineering of all kinds of thermoplastic structures, mainly tanks, septic ones and vessels, both above and under the ground. 15 years of practical experience in this field have given us the extraordinary position of being an expert in plastic vessels, FEA analysis, computer design, production technology and welding of all kinds of plastic materials. More then 800 of projects have been carried out, not only in Czech and Slovak republic but also in Austria and Germany, including expert appraisals of failures Number of employees = 1. Project description An aboveground welded thermoplastic scrubber had to be built in a draining piping system for gas waste products from a technological process. The vessel is equipped by a nozzle system for spraying liquid in the washing process of waste gas. Technical data diameter 1800 mm height 4350 mm weight 750 kg Program ESA-Prima Win version 3.60 Modules Linear static analysis of shells Intersections Stability of shells Intelligent document Analysis description Plastics structures exhibit a viscoelastic behaviour, dependent on the time of load exposition, the temperature and stress level reached in the material. The analysis of the thermoplastic starts with the long term strength and creep modulus determination. The number of analysis necessary is then related to these conditions. In the case of this scrubber, 2 crucial states were defined - the working state and the short term loads states. Both states have the same geometry and model of construction but differ in the modulus of elasticity and in the allowable stresses. As a result 2 independent linear analysis and 2 stability analysis were performed - a working state of the construction with the creep modulus 270 Mpa and the impact of the short term loads with the creep modulus 770 MPa. 2 documents - working state and short term loads, are enclosed. Experience The design of thermoplastic process equipment, using the appropriate design parameters and material properties can be completed with a combination of hand calculations and computer run Finite Element Analysis (FEA). FEA is necessary to determine peak stresses at discontinuities, corner joints, and to verify strain limits etc. For a complete FEA analysis, which has to be executed for thermoplastic process equipment, a non-linear analysis should be accomplished. However, this is usually impractical due to time, lack of detailed material strength design data, and the relatively low allowable design stresses used. Satisfactory designs have been consistently accomplished by using a linear elastic FEA approach and by using a constant on required years of durability dependent creep modulus value for the design allowable stresses. Measurements of fabricated thermoplastic structures indicate the linear elastic approach to be a viable and relatively accurate prediction of equipment stresses and deformations. Conclusion A complicated shape of thermoplastic vessels requires powerful tools for simplifying the creation of the geometry - intersections are a necessity. Several linear solutions of the structure, varying from creep modulus in relationship to the temperature, time of load exposition and reached stress level must be analysed. Each of the linear analysis must also be complemented by a stability check of the construction for the same creep modulus value. Sometimes the stability analysis does not give the positive values of the critical factors, depending on the geometry, loads and supports. Then the geometrical non-linear analysis must be used to find out the remaining load bearing capacity of the structure, several nonlinear analysis with regularly increased loads have to be performed till the collapse of the solver gives the critical load factor value. The number of equations solved normally varies between 100.000 - 1,000.000. So the requirements for a really fast solver are great, mostly the iterative solver is used. All mentioned features are included in ESAPrima Win software, the best solution for FEA of the thermoplastics vessels I have ever used. 66 Company Project Thermoplastic Scrubber SCIA User Contest 2005 / Civil Engineering 2 Categorie
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