This technical article was written by Yusuke Nishi, Senior Technical Services Engineer, Belzona. Part two is available here.
In the past, the repair of deteriorated pipework involved the welding of plates and sleeves, the use of bespoke clamps or the partial replacement of the faulty section. In recent years, however, the use of polymeric composite materials for the repair of pipes has gained worldwide support and interest. The main reasons for this are: the composite repair can be based on engineered structural calculations in accordance with internationally recognised standards; unlike welding, it is a safe cold process that can be carried out in areas where hot work is prohibited; it can be carried out at lower cost and provide long repair life sufficient to be taken as a permanent repair.
This paper describes Belzona SuperWrap II, including details of various tests conducted on the system to comply with both ISO 248171 and ASME PCC-2 (Article 401)2, the two major international standards for composite pipe repair.
Pipelines, especially those of large diameter, can efficiently transport large volumes of liquids and gases over long distances. Operating over long distances through various landscapes, environments and conditions, pipelines can be subject to internal and external effects from numerous factors. Differences in height cause internal pressure fluctuations, while changes in temperature cause the pipe material to expand and contract; from these behaviours, pipelines are subjected to physical loads such as bending, shear, torsion and fatigue. At the same time, the inner walls of the pipes can be exposed to corrosion and chemical attack, depending on the chemicals 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 also have disastrous consequences, meaning shutdowns and environmental impact. For this reason, it is incumbent on facility owners and operators to take proactive precautions to prevent the worst from happening.
Belzona SuperWrap II composite repair
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.
Two material properties are key to the development of composite materials for the repair of wall thinning and leakage defects in pipes: 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). In the case of polymeric composites, the mechanical strength and stiffness depend to a large extent on the properties of the reinforcing fibre. The resin is responsible for transferring the load between the reinforcing fibres. The success of a composite repair also depends on the adhesive strength of the resin, as it must be integrated with the pipe substrate.
In the development of the Belzona SuperWrap II, several combinations of resins and reinforcing fibres were considered. In the end, a two-component epoxy resin with 100% solids content, consisting of a phenolic novolac base (main agent) and an amine solidifier, was chosen. The main reason for this was the emphasis on 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.
In general, epoxy resins are slow to cure at low temperatures, but when heat is applied, the reaction is activated and the resin cures in a shorter time. Taking into account the temperature conditions at the time of application, which tend to be affected by climatic differences, two types of resin were initially developed (Belzona 1981 and Belzona 1982 resins), followed by Belzona 1983 resin with improved heat resistance (see Table 1). Today, three different types of resin are available, allowing the user to select the most suitable material depending on the temperature conditions.
|Belzona 1981 resin||Belzona 1982 resin||Belzona 1983 resin|
|Max Service Temperature||60°C||80°C||150°C|
The most suitable reinforcing fibre material was selected on the basis of the material’s mechanical strength and stiffness, as well as its workability (cutting, resin impregnation, on-site handling, etc.). After carefully considering all the pros and cons of each material, it was decided to use a hybrid fibre, a combination of carbon fibre and glass fibre, which is produced as Belzona 9381 to be an optimised reinforcement fibre sheet for Belzona SuperWrap II.
Belzona 9381 reinforcing sheet has a two-layer construction, with carbon fibre on the front and glass fibre on the back, to maximise the benefits of both fibres and to achieve the most efficient distribution and arrangement in terms of physical properties and workability. This is because the glass fibre and epoxy resin layer are designed to act as an insulator to prevent corrosion currents from flowing through the conductive carbon fibre. The reinforcing fibre sheets are available in several different widths to accommodate different pipe diameters, with wider sheets being particularly useful for special geometries such as bends, tees, flanges, reducers, as well as the walls and roofs of large storage tanks.
After the resin-impregnated reinforcing fibres have been wrapped around the pipe, a special consolidating film called Belzona 9382 is used to hold the repair in place until the resin has cured. Once the resin has cured, the film can be easily removed.
Yusuke Nishi is a Senior Technical Services Engineer for Belzona Asia Pacific based in Thailand. Yusuke has been with the company since 2011. He is an experienced professional within the plant maintenance industry specialising in composite repair and protective coatings. He possesses in-depth technical knowledge in various areas of polymeric solutions with a focus on corrosion management and problem solving, gained from over 10 years of experience at Belzona.
1 ISO 24817:2017, ‘Petroleum, Petrochemical and Natural Gas Industries – Composite Repairs for Pipework – Qualification and Design, Installation, testing and Inspection’
2 ASME PCC-2:2018, ‘Repair of Pressure Equipment and Piping’
Content Creator, Belzona Polymerics Limited