Assignment task: As a member of the safety and reliability-engineering group at a polymer manufacturing facility, you have been asked by the high-density polyethylene (HDPE) group to design and subcontract the construction of a laboratory scale cylindrical polymerization reactor to make HDPE in no more than 4 weeks. They need to start some trials as soon as possible to develop a new HDPE grade for a high volume loyal customer.
The maximum design temperature and pressure of the reactor are 200°C and 25 MPa. respectively. The reactor will be used 4 times per day and must be designed for a minimum lifetime of 20 years. Based on past experience, space constraints and desirable amount of HDPE made during each run of the reactor, the HDPE group wants the inside diameter and wall thickness of the reactor to be 300 mm and 10 mm, respectively.
According to the laboratory safety regulations of your company, a safety valve must be installed to make sure the reactor pressure does not exceed 22 MPa. If the valve is activated, it will result in a sudden in maximum drop of temperature of 220 0C in the valve region. The reactor must not plastically deform according the Von-Mises yield criteria. It must also be designed based on a leak-before-break approach.
Choose a suitable engineering alloy to make a reactor that meets the design and safety requirements. If you cannot find a suitable engineering alloy, consider increasing the thickness of the reactor to ?nd a suitable candidate.
Make sure to clearly specify the quality and material property requirements of the reactor material.
Table 1 through 3 provide sample material properties but you may use other data sources to broaden the choice of material (i.e., ASM Handbooks, vendor material property sheets, MatWeb, etc.) Assume a geometry factor of f = 1.5 for the stress intensity factor.
Based on the current availability of pressure relief valves, you know that even if the reactor can be built in less than 4 weeks. the pressure relief valve will not be delivered in less than 6 weeks. When you mentioned this issue to your boss, he told you that the HPDE group must present some preliminary demonstrations to show progress of the development of the new HDPE grade to the customer in 6 weeks. He also said the reactor could be run temporarily, without a pressure relief valve. by implementing a pressure controller that will shut down the reactor if the pressure reaches 22 MPa. After checking the laboratory safety regulations, it is very clear to you that a safety valve must be installed to operate the reactor.