Polyethylene piping materials

EN 12099 Polyethylene piping materials and components - determination of volatile content. 

EN 12099 1997 Plastics Piping Systems - Polyethylene Piping Materials and Components - Determination of Volatile Content... 

Fig. 32.2 shows an example of hydrostatic stress rupture curves (time vs. hoop stress) for a typical polyethylene piping material where elevated temperature testing demonstrates this change in failure mechanism. Fig. 32.2 shows the development of a second type of failure mechanism (brittle or slit-type failures) for the higher-temperature testing data (60 and 80°C). The ambient temperature test data (23°C) will show a similar downturn of the curve as a similar transition from ductile to brittle failure mechanism also occurs. But this does not happen until much... 

Figure 32.2 Typical stress rupture testing curves for a polyethylene pipe material.

In order to address the possibility of a loss of ductility in polyethylene piping materials, the Hydrostatic Stress Board of the Plastics Pipe Institute developed the validation testing concept to ensure that... 

In 1984, the GRI published a study that compared and ranked several commercially extruded polyethylene piping materials produced after 1971 [64]. Again, the materials tested were identified by codes. Stress rupture tests were performed using methane and nitrogen as the internal pressure medium and air as the outside environment. Several stress rupture curves showed early transitioning from ductile to brittle failure modes. 

Mruk, S. and Palermo, E., The Notched Constant Tensile Load Test A New Index of the Long Term Ductility of Polyethylene Piping Materials, summary of presentation given in the Technical Information Session hosted by ASTM Committee E17 s task group on Project 62-95-02, held in conjunction with ASTM Committee E17 s November 1996 meetings. New Orleans, LA. 

He X, Cai Y, Wang Q, et al Improvement of mechanical properties and ultraviolet resistance of polyethylene pipe materials using high density polyethylene matrix grafted carbon hhek, JMaeromol Sci Phys 51(2) 298—312, 2012. 

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. 

Standard specification for polyethylene pipe and fitting materials... 

The equilibrium sorption and diffusion coefficient were determined for toluene and tetrahydrofuran in oriented linear polyethylene pipe produced by hydrostatic extrusion The results, which are summarised in Table 4, show that the sorption is about a factor of ten less than that for isotropic material, and the diffusion coefficients are a factor of a hundred less. It is clear from these results, taken in conjunction with those for gases discussed above, that the improvements in barrier properties increase with molecular size. This can be attributed to the increased difficulty of penetrating the structure as the molecular size increases. 

On cooling, plastic materials tend to contract or shrink considerably more than other materials such as metals, ceramics and glass. For example, a copper pipe will shrink by 0.01% if the temperature is reduced by 10°C. Under the same conditions, a high-density polyethylene pipe would shrink by 0.07%, and polypropylene and hard PVC pipes by 0.04%. In addition, surfaces of plastic materials cool before their cores. Such a situation leads to the initial contraction of plastic materials at surfaces, before significant change in dimension occurs in the bulk. The skins of moulded plastics tend to be stiffer than the bulk, so are more prone to degradation by mechanical action, e.g. flexing. 

It was determined that plastic materials PVC and polyethylene (PE) promoted biofdm growth better than mild steel (Schwartz et al., 2000). Similar density of fixed bacterial biomass on PVC and polyethylene was proved (Niquette et al., 2000), but the other study found that pipe material influenced biofilm activity far less than chlorine with biofilm growth ranked in the order glass < cement < PE < PVC (Hallam et al., 2001). 

Ground coupled heat pumps may now be feasible, largely due to the availability of durable and Inexpensive plastic pipe. Pipe materials such as polyethylene, FVC, and polybutylene have been found to be adequate In some Instances. However, no material standards or recommended design practices exist to facilitate the optimization of the performance, cost and reliability of these systems. 

D 2766 (1995) Test method for specific heats of liquids and solids D 3286 (1991) Test method for gross calorific value of coal and coke by the isoperibol bomb calorimeter D 3350 (1999) Polyethylene Pipes and Fitting Materials D 3386 (1994) Test method for coefficient of linear thermal expansion of electrical insulating materials D 3417 (1999) Test method for heats of fusion and crystallization of polymers by thermal analysis D 3418 (1999) Test method for transition temperatures of polymers by thermal analysis... 

There many reasons to add plasticizers to the polyethylene formulations. Smaller amounts are added for conventional reasons, such as to make material more flexible. This includes applications in hotmelt adhesives and plasticization of pipe material. It is shown that up to 30 phr of plasticizer can be added to polyethylene. Small amounts of plasticizer are also needed to compatibilize different polymers or formulation components as well as to facilitate the biodegradative properties. ... 

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