New Practice for Heat Butt-Fusion Joining of Very Thick Wall (>2-inches) Bi-modal High Density Polyethylene Pipe and Fittings for Industrial and Municipal Applications.
1. Scope
Introduction :
HDPE is an autohesive polymer which wants to stick to itself in its molten state by contact molecular-diffusion of two melt-surfaces. With the increase in use of bi-modal polyethylene pipe and fittings in larger diameters and lower DR’s in recent years, the pipe wall thicknesses have become much thicker, often being 2.5-in thick to 8-in thick. In very thick-wall bi-modal HDPE pipe, the radial elongation of molten molecules in the fusion joint melt-flow-zone (MFZ) is much greater than in pipe walls less than 2-inches thick. To mitigate the effects of severe radial molecular elongation across the melt flow zone (MFZ), lower fusion pressures are required to develop complete fusion joining with reduced radial molecular orientation. The fusion pressure ranges specified here-in have been globally adopted by fittings fabricators, and very thick-wall bi-modal HDPE pipe manufacturers.
1.0 Scope
1.1 This Standard Procedure establishes the general steps and specific procedures used for the construction and quality assessment of butt fusion joints for very thick-wall pipe and fittings, made with well maintained fusion machines of sufficient power and force to join them, both in a factory and in field construction. This Standard Procedure establishes a range of qualified procedures known to work with thick-wall bimodal pipe and fittings.
1.2 The temperature and pressure range parameters here-in are applicable to joining of polyethylene bi-modal resins of similar density and melt-viscosity (Melt-index). `
1.3 Components to be joined are required to be within the dimensional tolerances of their nominated pipe and fittings standards, such as ASTM F714, AWWA C906, ASTM F2619, ASTM F3123, ISO 4427, and EN12201, for listed sizes and DR’s, as well as for custom diameter pipe sizes and DR’s permitted there-in.
Keywords
butt-fusion, PE4710, Thick-wall, HDPE, Pipe, single pressure , Industrial and Municipal
Rationale
HDPE is an autohesive polymer which wants to stick to itself in its molten state by contact molecular-diffusion of two melt-surfaces. With the increase in use of bi-modal polyethylene pipe and fittings in larger diameters and lower DR’s in recent years, the pipe wall thicknesses have become much thicker, often being 2.5-in thick to 8-in thick. In very thick-wall bi-modal HDPE pipe, the radial elongation of molten molecules in the fusion joint melt-flow-zone (MFZ) is much greater than in pipe walls less than 2-inches thick. To mitigate the effects of severe radial molecular elongation across the melt flow zone (MFZ), lower fusion pressures are required to develop complete fusion joining with reduced radial molecular orientation. The fusion pressure ranges specified here-in have been globally adopted by fittings fabricators, and very thick-wall bi-modal HDPE pipe manufacturers.
WK85672 - New Practice for Heat Butt-Fusion Joining of Very Thick Wall (>2-inches) Bi-modal High Density Polyethylene Pipe and Fittings for Industrial and Municipal Applications. | ASTM
