The Benefits of Using High-Temperature GFRP Pipe

Glass Fiber Reinforced Plastic (GFRP) pipes are widely used as polymer-based composite pipes in various engineering fields where the temperature influences their performance. This paper investigated the circumferential bending properties of GFRP pipes with different continuous fiber contents at 30 °C, 50 °C and 70 °C. GFRP pipes are classified into three types according to their component content: type I, type II and type III. The results show that the bending performance of GFRP pipes tends to decrease with increasing temperature, with the retention of circumferential stiffness being 80&#;85% and the retention of bending strength and damage displacement being about 25&#;40% from 30 °C to 70 °C. The rate of decay of ring stiffness, bending strength and damage displacement is significantly higher from 30 °C to 50 °C than from 50 °C to 70 °C. Both temperature and continuous fiber content greatly influenced the damage pattern. At 30 °C, delamination damage occurred at the top and bottom of the Type I GFRP pipe before fracture damage happened at the left and right ends and fracture damage occurred at both the left and right ends of Type II and Type III GFRP pipes. Delamination damage happened at the upper and lower ends of the GFRP pipes at 50 °C and 70 °C. In addition, the paper analyses the mechanisms of the associated effects.

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1. Introduction

Glass fiber reinforced polymer (GFRP) pipes have the advantages of light weight, high strength and corrosion resistance [1,2,3] and are widely used in various industries such as municipal engineering, petrochemical, marine engineering, nuclear engineering, aerospace and automotive [4,5,6,7,8]. A typical GFRP pipe structure consists of three layers: an inner layer, a structural layer and an outer layer. The inner and outer layers are usually made of unsaturated polyester resin, with a structural layer composed of GFRP composites sandwiched between the above two layers [9]. The GFRP pipe used in this paper is made of glass fiber and its products as reinforcing materials, unsaturated polyester resin and other matrix materials and inorganic non-metallic granular materials such as quartz sand and calcium carbonate as fillers, using a continuous winding process method.

Up to now, most studies on the stiffness of GFRP pipes have been conducted mainly under ambient conditions. Zhu et al. [10] experimentally verified the theoretical calculation of the stiffness of a new sandwich-reinforced pipe structure using a flat plate compression test, a finite element model of the sandwich pipe structure was also developed to simulate the compression test and different damage modes were discussed. Chen et al. [11] studied the stiffness of GFRP pipeline under different winding modes and load conditions, established the stiffness degradation model of GFRP pipeline and obtained the parameters of the model. Tu et al. [12] reduced the elastic modulus of GFRP reinforcement by monitoring the strain of GFRP reinforcement in real time and then modeled the degradation of the elastic modulus of GFRP reinforcement in an alkaline, corrosive environment and proposed a relationship between the tensile strength and the elastic modulus of GFRP reinforcement. Rafiee et al. [13] used a simple analytical model based on solid mechanics to estimate the stiffness of the investigated pipes, which in turn predicted the stiffness of GFRP pipes under lateral compressive loads. As research on the stiffness of GFRP pipes at different temperatures is still limited, this paper investigates the effect of temperature on the stiffness of GFRP pipes.

Temperature is an important parameter affecting the mechanical properties of GFRP. Robert et al. [14] investigated the tensile, shear and flexural properties of GFRP steel reinforcement at low temperatures from 0 to 100 °C and at high temperatures from 23 °C to 315 °C, the effects of extreme temperatures on the fibers, matrix and fiber/matrix interface were also investigated and the results showed that the mechanical properties of the composites, especially the stiffness and strength, decrease significantly at very high temperatures close to the glass transition temperature of the polymer matrix. Solyom et al. [15] conducted an experimental and analytical study of the bonding behavior of 8 mm diameter GFRP bars embedded in concrete and exposed to temperatures ranging from &#;20 °C to 300 °C. Vieira et al. [16] investigated the effect of medium/high-temperature exposure on the residual flexural properties of different types of GFRP commercial pultruded materials. Hosseini et al. [17] initially investigated the tensile strength and modulus of elasticity of four different diameters of GFRP tendons under a four-point bending test at 20 °C. They obtained the tensile strength of different diameters of GFRP tendons at low and high temperatures (&#;40 to 80 °C) by a four-point flexural test. Lobanov et al. [18] analyzed the degradation of elastic modulus, tensile strength, Poisson&#;s ratio and strain corresponding to the strength limit with increasing temperature at 22 °C, 100 °C, 175 °C, 250 °C and 300 °C. Liu et al. [19] investigated the bending damage loads, deformation modes and damage mechanisms of carbon fiber-reinforced polymer composite pyramidal truss core sandwich structures in the temperature range of 20 °C to 200 °C; bending stiffness and damage loads were also predicted at different temperatures. Dutta et al. [20] investigated glass fiber-reinforced polyester composites&#; tensile and compressive behavior under continuous loading and high temperature. They also developed a simple empirical model using curve-fitting equations to predict failure times. Ashrafi et al. [21] investigated the tensile properties of different GFRP laminates at high temperatures using fiber structure, exposure temperature and laminate thickness as test variables and damage to the resin, fibers and their interfaces was investigated. However, there is still a lack of research on the bending properties of GFRP. Therefore, this paper examines the effect of different temperatures on these bending properties. Yu et al. [22] used different types of epoxy adhesives and FRP bars to prepare NSM FRP specimens and tested the bond strength in the temperature range of 20&#;400 °C. The experimental results show that the bond strength and modulus decrease significantly in the temperature range of 20~200 °C and only maintain 20~30% of their original values at 200 °C. Correia. et al. [23] studied the tensile, shear and compression responses of GFRP materials at temperatures ranging from 20 °C to 250 °C and analyzed the load-deflection curve, stiffness, failure mode and ultimate strength of GFRP materials. The experimental results show that, due to the glass transition of the resin, the mechanical properties of GFRP deteriorate seriously under moderately high temperatures, especially under shear and compression loads. In Parodi et al. [24], the effect of the thermal history on Tg was investigated by means of fast scanning calorimetry (flash-DSC). The analysis led to the conclusion that the thermal history affects the ratio between rigid and mobile amorphous phases and it is this ratio that determines the glass transition temperature of dry polyamide 6. Alsayed et al. [25] studied the effect of temperature rise on the degradation mechanism of GFRP bars. The results show that the increase in temperature will affect the resin matrix around the glass fiber and thus affect the binding between the fiber and the matrix.

In addition, previous studies have revealed that the fiber volume fraction has an essential effect on the mechanical properties of GFRP pipes. Rafiee et al. [26] investigated the damage process and failure mechanism of GFRP pipes under transverse compressive loading. They found that increasing the core thickness would accelerate in-plane failure and delamination in the pipes. The negative effect of increasing the fiber volume fraction could be compensated by adjusting the winding angle of the cross-ply. In addition, they [27] carried out stochastic modeling of the uncertainty in the discontinuous fiber winding process and found that the effect of changes in fiber volume fraction on the functional failure pressure of GFRP pipes was more pronounced than changes in the winding angle of the spiral plies. Ray et al. [28] investigated the effect of varying the wet thermal conditioning cycle on the moisture gain/loss kinetics and interlaminar shear strength (ILSS) of glass fiber-reinforced epoxy and polyester matrix composites with different mass fractions. However, there is a lack of relevant research on the effect of continuous fiber content on the flexural properties of GFRP pipes. Therefore, this paper further investigates the impact of constant fiber content on the flexural properties by comparing three different types of GFRP pipes.

Most studies have focused on the mechanical properties of glass fiber-reinforced polymers at different temperatures. At the same time, there is a lack of research on the bending properties of different types of GFRP pipes at different temperature conditions. The study of the influence of various factors on these bending properties is of great significance for the structural safety of pipes. Therefore, this paper presents an experimental study of the circumferential bending performance of GFRP pipes with different continuous fiber contents by conducting flat plate external loading experiments at three different temperature conditions of 30 °C, 50 °C and 70 °C. The results of this study will help researchers and design engineers to improve their understanding of the flexural properties of glass fiber-reinforced polymers.

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FRP and dual laminate piping and tank liners typically feature a smooth interior surface. This smoothness minimizes friction and prevents the accumulation of deposits or scaling, which can lead to improved flow efficiency and reduced maintenance needs.

In addition to these features, FRP is a non-conductive material, making it suitable for applications where electrical conductivity is a concern. Composite piping is also highly customizable. It can be tailored to meet specific project requirements, including diameter, length, and special features like insulation, fire resistance, and abrasion resistance.
Low thermal conductivity is another benefit of FRP. It is most desirable in applications where maintaining temperature control or insulation is essential.

Thanks to its inherent resistance to corrosion and its long-term durability, FRP piping typically requires minimal maintenance compared to RLCS, SS, and alloys, which require regular, scheduled cleaning and coating to maintain corrosion resistance. While the initial cost may be higher than some other materials, the long-term advantages of FRP and dual laminate piping, i.e., reduced maintenance, longer service life, and corrosion resistance, along with the total cost of ownership, can make it the better choice for your operation.

Ultimately, the suitability of FRP piping depends on the specific application and environmental conditions. Careful consideration of project requirements and constraints is essential. Proper design, installation, and maintenance practices are also crucial to realizing the full benefits of FRP and dual laminate piping.

For a more thorough comparison of dual laminate and lined steel, please take a look at our technical bulletin.

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