The effect of the wall thickness variation of blow-moulded bodies made of high-density polyethylene on an internal pressure test after prestoring the packaging with standard liquids was evaluated in experiments and simulations. The objects of the investigation were jerrycans used for the transportation and storage of dangerous goods.The wall thickness was determined using two alternative methods to the magnetostatic measurement. These alternative methods are used for research purpose to get a volumetric model of the jerrycan wall as a geometric model for the simulation. The comparison of the experiments and the simulations of the internal pressure test were performed using the digital image correlation method. The integral strain and deformation of the whole jerrycan was detected by measuring the total mass of the jerrycan being filled with water during the internal pressure test. This is a suitable alternative to the optical measurements of local deformation by the digital image correlation method. Prestorage at 40 C without the influence of chemicals strengthens the jerrycan, whereas the swelling effect of butyl acetate and hydrocarbon mixture softens the jerrycan. The comparison with the experiment is necessary to verify the accuracy of the simulation. It shows that the deformation can be simulated more precisely by using the actual measured geometry. The weakening of the high-density polyethylene caused by a hydrocarbon mixture can be simulated using the Arrhenius equation. The aim of the simulation was to discover whether it is possible to use specimens to predict the behaviour of a packaging both after the influence of standard liquids.
A guided drop test was performed to achieve a defined and reproducible impact orientation of jerrycans. The drop heights where 50% of the jerrycans experienced a failure from a crack where fluid can escape (50% failure drop height) were compared among jerrycans made of four different materials, in their original state and preconditioned with standard liquids. To analyse the impact of only elevated temperatures, the packages were preconditioned for 21 days at 40 C without the use of chemicals.The 50% failure drop height was compared by using Young's modulus; the notched impact strength (NIS) of specimen cut from plates which were manufactured by compression moulding and the notched tensile impact strength of specimen cut-outs of the jerrycans' side walls. The NIS depends highly on the thermal preconditioning of the plates being manufactured by compression moulding. A trend can be seen that a higher Young's modulus, a higher NIS and a higher notched tensile impact strength result in a higher 50% failure drop height, but the values are spread. The influence of the wall thickness cannot be neglected.The change of the 50% failure drop height in regard to the preconditioning at 40 C with and without nitric acid was compared in terms of their resistance to molecular degradation, density and degree of crystallinity. The conditioning at elevated temperature causes post-crystallization. It was shown that the resistance to molecular degradation determined on pressed plates correlates with the change of the 50% failure drop height after pre-storage with nitric acid.
Safety risks may ensue when the chemicals contained in polyethylene packagings a age and damage them. To prevent subsequent accidents, the European Dangerous Goods Regulations have laid down requirements for testing the chemical compatibility of liquid dangerous goods transported in polyethylene packagings. The test procedures include 6 months in which the chemical is prestored in the packaging. After this time, the respective design-type tests are performed. Alternative methods with so-called standard liquids, simulating the different types of damaging effects, are also possible. If a packaging has successfully passed the design type tests with a standard liquid, other dangerous goods may also be transported in this packaging, as long as it is demonstrated that they have a less damaging effect than the standard liquid. However, in this area there is only little information and research available.A new potentially effective and time-saving method for comparing the stress crack damaging influence of liquids with standard liquids was proposed by a major German chemical company.The validation of this method, which was carried out on two polyethylene materials, showed the general applicability of the method. Two kinds of wetting solutions were applied to simulate cracking under stress.The influence of prestorage, test temperatures, wetting agents and material was examined. FEM calculations were carried out to ascertain the influence of the sample shape.
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