Pressure Pipes

Plastic pressure piping is used for many industrial processes, heating and cooling installations, gas distribution, irrigation, and water supply and distribution. Potable water applications include cold water services from wells or water mains, as well as hot and cold water distribution piping within buildings. Typical requirements Pressure pipes must perform under extreme testing conditions, because failure can lead to major safety risks. Lifetime: a minimum of 50 years Pressure: based on material classification and intended application Temperature: 20-40°C Outside diameter: 10-1600 mm

• Material strength and pressure rating/design stress: Material classification is based upon testing pipe at varying stress levels and at different temperatures. Taking into account the relationship between geometry, stress, and pressure at various temperatures, regression analysis following ISO 9080 is carried out to determine the long term hydrostatic strength (LTHS) of the thermoplastic pipe. Safety factors have also been established by practical experience, but are only considered a minimum for each application. Each project needs to consider the operational requirements of the pipeline system, taking into account other potential and uncontrollable factors, such as pressure surge, operational temperatures, the material to be conveyed by the pipe, land settlement, etc.
  
  
• Long-term performance: Long-term performance is generally governed by the slow crack growth (SCG) properties of the material. The molecular architecture of today's pipe resins make them extremely resistant to SCG. To determine the SCG properties of a resin suitable for pipe applications in a reasonable time-frame, a test method of notching the pipe and testing under stress has been developed: ISO 13479.
  
  
• Rapid crack propagation: Under the action of internal pressure, and hence potential energy, a crack can spread along the length of a pipe at almost the speed of sound. This phenomenon is called Rapid Crack Propagation (RCP). RCP failure is dependent on pipe diameter, wall thickness, temperature, internal pressure, and source of impact. The two types of RCP tests accepted by the industry include small scale steady state (S₄ ISO 13477) and full scale testing (FST) as developed by British Gas (ISO 13478).
  

Environment
Current environmental concerns in this sector primarily relate to waste. Precious resources such as water and gas cannot be allowed to go to waste, and an effective pipe management system is vital. PE pipelines are designed to last for 50 years or more, allowing an inert, low-maintenance system to transport vital liquids in a leak- and corrosion-free environment.

Clean PE pipes may be recycled and used in other non-pressure pipe applications.

Applications and relevant Dow resins
Dow offers a range of pipe resins that meet the demands of ASTM, CEN, and ISO standards for pressure pipe materials and applications.

New bimodal polyethylene resins in North America offer considerably improved hoop stress properties and resistance to rapid crack propagation (RCP) and slow crack growth (SCG), opening up new opportunities for PE pipe.

Dow is also focused on research and development for the pressure pipe market with plans to deliver new commercial solutions to the European marketplace within three to five years.