Yusuke Nishi, Senior Technical Service Engineer, Belzona, Thailand, introduces an ISO/ASME compliant composite repair system for pipes.
Pipelines, especially those of large diameter, can transport large volumes of liquids and gases over long distances at high efficiency. Operating over long distances through various landscapes, environments and conditions, pipelines can be subject to internal and external effects from numerous factors. Changes in temperature cause the pipe material to expand and contract, while differences in height cause internal pressure fluctuations. From these behaviours, pipelines are subjected to physical loads such as bending, shear, torsion and fatigue. At the same time, the pipe walls can be exposed to internal corrosion and chemical attack, depending on the chemical solutions involved in the media. Similarly, under conditions of inadequate protection, pipes are also subject to external corrosion.
These effects, acting alone or in combination, can cause damage to the pipe wall in the form of metal loss and eventually lead to through-wall defects, leading to leakage problems. Leaks can result in disastrous consequences such as shutdowns and environmental impact. For this reason, facility owners and operators must take proactive precautions to guard against such damage before the worst occurs.
Belzona SuperWrap II is a pipe repair technology based on a polymer-based composite of epoxy resin and reinforcing fibres, using a wet-wrapping technique in which the resin-impregnated reinforcing fibres are wrapped directly around the pipe defect and cured.
Composite materials for the repair of wall thinning and leakage defects in pipes are reliant on two material properties: mechanical strength and stiffness. Mechanical strength depends on the maximum tensile stress that a material can withstand without failure and is determined from its tensile strength. Stiffness, on the other hand, refers to the elastic deformation of a material when a force is applied and is defined by the Young’s modulus (also known as tensile modulus or modulus of elasticity). The mechanical strength and stiffness of polymeric composites depend largely on the properties of the reinforcing fibre. The resin is responsible for transferring the load between the reinforcing fibres. The resin must be integrated with the pipe substrate, making the material’s adhesive strength key to the success of a composite repair.
Several combinations of resins and reinforcing fibres were considered in the development of Belzona SuperWrap II. A two-component epoxy resin with 100% solids content, consisting of a phenolic novolac base (main agent) and an amine solidifier, was ultimately chosen. This was primarily due to the fact that epoxy resins can achieve better adhesion and mechanical strength compared to other functional polymer groups, including polyurethanes, methacrylates, alkyds, vinyls and polyesters. The possibility of forming highly cross-linked polymer matrices, which are the basis for excellent heat and chemical resistance, should also be supplemented as one of the reasons for concluding that phenolic novolac epoxy resins are the best choice …
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