Pipe materials, HDPE

The application areas of bimodal polyethylenes are the same as for corresponding uni-modal resins. However, improved product property combinations, such as stiffness-impact balance, result in products with higher performance. For example, without bimodal polyethylene and control over the MWD and comonomer incorporation, development of HDPE pipe materials with higher pressure classification would not have been possible [15, 16]. Another new opportunity is material reduction (source reduction) without compromising the properties of the ready-made plastic products. Depending on the end use, e.g. in film application a thickness reduction of 10-30% is possible. 

In addition, it is shown that, plastic pipes in the house and out (such as underground), all show good resiliency in the case of earthquakes that beats all other traditional materials available (Valencia Water Company, USA, the California private utility was able to compare the performance of three pipe materials - asbestos-cement, PVC and steel, during the catastrophic Northridge earthquake of January 1994, and found that PVC outperformed the others). Since the Kobe earthquake, which showed the structural weakness of traditional pipes, HDPE pipes are preferentially being used as gas pipes [2]. 

PE (beginning from low-density PE (LDPE), medium-density PE (MDPE) and especially high-density PE (HOPE)) are mainly nsed for piping (mainly for pressure pipe production) and floor coverings in the constrnction indnstry. Plastic pipes provide a reduced number of joints, and in addition, PE pipes are preferred because of the inertness and mechanical properties of the material. However, HDPE has the greatest coefficient of thermal expansion (CTE) value of any plastic pipe material, almost three times that of PVC, which is one of its main drawbacks in constrnction applications. HDPE is commonly used in perimeter drain pipe around fonndations, but rarely inside houses. 

The Moody diagram is a general graph for the Darcy factor versus the Reynolds number, It is applicable to a very large number of different pipe materials. There are four principal pipe materials associated with slurry flows plastic pipes [high-density polyethylene (HDPE)], plain steel pipes, rubber-lined steel pipes, and concrete pipes. The absolute... 

The dimensions of plain HDPE pipes (not HDPE-lined steel) for pressures up to 110 psi (760 kPa) are listed in Table 2-4. The dimensions of HDPE pipes for pressures in the range of 125 to 300 psi (863-2070 kPa) are presented in Table 2-5. These dimensions are slightly different than metric pipes. HDPE is not a magic material but can withstand the abrasion of taconite and some coarse laterites. M with rubber, there must be a cut-off size of particle size beyond which the use of HDPE is not acceptable. Very little has been published on this subject. 

Two HDPE pipe material samples PE-1 and PE-2 with different longterm mechanical properties were fuUy characterized by means of the above-mentioned two combined methods. The physical and mechanical properties of the two HDPE samples are Usted in Table 3.1. Apparendy, PE-2 sample showed a much larger ESCR value than that of PE-1. 

PE-1 was slightly higher than that of PE-2, but the opposite situation occurred in the high temperature fractions of these two samples. It was demonstrated that lower the content of comonomer in the low MW parts and increase the content of comonomer in the high MW parts would be crucial in order to achieve much better long-term mechanical properties of the HDPE pipe materials. 

The HDPE/CB and HDPE/HDPE-g-CB composites were thus prepared by mixing the HDPE pipe materials with pristine CB and... 

It was found that the HDPE/HDPE-g-CB composites generally showed better tensile properties than that of the HDPE/CB composites. For the HDPE/HDPE-g-CB composite with CB content of 5.0 wt%, the tensile strength and ultimate strain were improved by 17% and 30%, respectively, as compared to HDPE/CB composite. The improvement of the tensile properties of the HDPE/HDPE-g-CB composites might be due to the enhanced crystallization, the improved dispersion state of CB in the matrix, and a more efficient load transfer from the pipe materials matrix to the CB nanoparticles induced by the HDPE-g-CB (Tang et al., 2003). 

The quantity of these materials is relatively small compared with the amount of waste high-density poly(ethylene) produced each year. Containers made from HDPE are widely used for detergents, oil, and antifreeze, and enormous amounts of material are used in disposable applications aimually. In principle recycled poly(ethylene) could be used for drain pipes, flower pots, dustbins, and plastic crates. The problem remains, however, that economics do not favour recycling of these polymers and in the absence of Government intervention little or nothing can be done to alter commercial attitudes towards recycling. 

The original perforated collector pipes in landfills were made of concrete like those used in highway underdrain systems. As landfills became higher, the strength of such pipes became inadequate. Today, perforated PVC pipes are commonly used, as are HDPE pipes. New regulations require that all materials be tested for chemical resistance as part of the permit-approval process. 

Coaxial push-out tests (DIN 53769-A) are typically performed on production run pipe samples for quality-controlpurposes. Typical results using oxyfluorinated HDPE as liner material are shown in Table 16.11 below. 

The most important application area of HDPE is the production of containers and injection molded articles. Bottles for detergents, gasoline cans and heating oil tanks are some examples. The most common use of HDPE for injection molded articles is for the production of storage and distribution containers, like buckets and bottle cases. However, processing into films and pipes has become increasingly more common. Films made out of HDPE possess high fat resistance (as wrappers for meat) and have better aroma barrier properties compared to lower density PE materials. 

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