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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.


Compliance with standards The Composite repair of pipework requires a high


degree of reliability, especially in the case of high pressure piping systems or for pipes carrying hazardous media. For this reason, rigorous third-party and in-house testing is carried out to demonstrate compliance with a series of requirements set out in ISO 24817 and ASME PCC-2. For the tests aimed at assessing the mechanical properties of the materials, plate specimens made of reinforcing fibre and each resin were used. On the other hand, in the pressure resistance test aimed at evaluating durability of the system, a short pipe spool with pseudo-defects of the specified dimensions was repaired with the system, followed by a pressure resistance test for confirmation. A summary of each test is given in Table 2.


Test results and verification Table 3 shows some results of the physical property


tests. In parentheses are the curing temperatures of the specimens. In the tensile shear bond strength test, the bond


strength of the resins is measured in two ways as: 1) cured for 7 days at specified temperature conditions (short-term condition), and 2) immersion in water for 1000 hours at specified temperature conditions (long-term condition), both using carbon steel as the adherend. The comparison of the results of the low and high temperature tests is intended to see the effect of temperature changes on the adhesive strength of the resins. All the results comply with the requirements of ISO 24817 in two respects: (a) The tensile shear bond strength of each resin is >5 MPa for short- and long-term conditions


(b) For each resin, the long-term values are at least 30% of the short-term values


The glass transition temperature (Tg) is the temperature at which a polymer material begins to soften as it is heated. It is a common phenomenon for thermoplastics and its value is often referred to in assessing the thermal properties and thermal resistance of resin-based repair techniques. When the resin is heated while it is curing, the density of the cross-linking increases and the glass transition temperature rises. When Belzona 1981 resin is cured at 60°C, Belzona 1982 resin at 80°C and Belzona 1983 resin at 150°C, the glass transition temperatures are


Table 2 – Test items and test methods Test items


Tensile properties Structural integrity Energy release rate Long-term strength Impact performance Thermal properties


Details


Tensile strength, tensile modulus, Poisson’s ratio, strain to failure


Wrapped pipe with defect to survive short term pressure test


Toughness parameter for the repair/ substrate interface


Long-term (creep rupture) strength of the repair


Test methods


ISO 24817 – Annex B ASTM D3039


ISO 24817 – Annex C ISO 24817 – Annex D ISO 24817 – Annex E


Low velocity 5 J impact performance ISO 24817 – Annex F Coefficient of thermal expansion Glass transition temperature


ISO 11359 ISO 11357-2


In-plane shear modulus Shear modulus by V-Notched beam method


Lap shear adhesion strength


< Short-term condition > Shear adhesion strength of resin bonded to substrate


< Long-term condition > Measurement of lap shear adhesion strength after 1000 hours of exposure to immersion


Table 3 – Composite properties assessment results Test items


Belzona 1981 resin


Short-term lap shear strength


Long-term lap shear strength


Glass transition temperature


Young’s modulus


Thermal expansion coefficient


15.5 MPa (20°C) 15.5 MPa (40°C) 90°C (60°C) 38.8 GPa (20°C) 9.44 x 10-6 /K ASTM D5379 EN 1465 EN 1465


Belzona 1982 resin


15.0 MPa (80°C) 19.0 MPa (40°C) 115°C (80°C) 38.6 GPa (20°C) 11.26 x 10-6 /K


Belzona 1983 resin


11.2 MPa (150°C) 10.3 MPa (150°C) 188°C (150°C)


36.9 GPa (150°C) 9.40 x 10-6


5.19 x 10-6


/K (20°C) /K (150°C)


90°C, 115°C and 188°C respectively (see Table 3). Piping systems under pressure are subject to the Poisson effect. Due to the circumferential stresses occurring inside the pipe, the diameter of the pipe increases slightly, but at the same time there is a contraction in the axial direction and the pipe becomes shorter. Therefore, a Poisson’s ratio close to the value of the pipe is required for the composites to be a suitable material to restore the mechanical strength of the pipelines. The Poisson’s ratio of the Belzona SuperWrap II material is close enough to


f


Left: In-field application of Belzona SuperWrap II on a corroded pipeline


www.waterpowermagazine.com | March 2023 | 45


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