Glass Fiber Reinforced Polymer Pipes Research Articles

Characterization of Wall-Loss Defects in Curved GFRP Composites Using Pulsed Thermography

Curved glass fiber–reinforced polymer (GFRP) composites are superior to alloy-steel pipes due to their excellent corrosive resistance properties, finding wide applications in the transportation of petrochemicals, chemical storage tanks, and power and water-treatment plants. Among the defects found in GFRP pipes, internal pitting or wall loss is one of the most severe, caused by material deterioration and the friction of small particles in the transfer fluid. This study investigates these in-service discontinuities using a pulsed thermal nondestructive evaluation technique. The paper focuses on the quantification of defect depth using the temperature peak contrast derivative and defect sizing using the full width at half maximum method. Further, the paper investigates the ability of pulsed thermography to estimate pitting or wall-loss defects at various depths and sizes through simulation and experimentation. Thermographic signal reconstruction images are used for quantification of defects at a deeper depth. The results of the present study are then compared with well-established ultrasonic C-scan results.

The effects of back-up on drilling machinability of filament wound GFRP composite pipes: Mechanical characterization and drilling tests

Composite structures used in many engineering fields are produced using different production methods according to the design characteristic. The filament winding (FW) method, one of the most important of these production techniques, is preferred in the manufacturing of high-pressure vessels, pressure pipelines, and construction components. Composite pipes produced by the FW method are assembled using various processing methods depending on their usage. Drilling is one of the most used method among these processing techniques. The drilling-induced damages negatively affect the mechanical properties of the composite pipes during service. Therefore, it is important to determine the optimum cutting parameters and a suitable back-up material so that minimal damage occurs during the drilling process. In this study, firstly, mechanical properties of the glass fiber reinforced polymer (GFRP) produced by the FW method at ± 55° configuration were determined and damage characteristic based on ring tensile test was analyzed. Then, the effects of back-up use on the drilling machinability of FW GFRP pipes were investigated. Results showed that back-up use in drilling composite pipes plays a key role in reducing delamination, borehole damages, and surface roughness although it leads to occur higher thrust forces. Also, it helps prevent the propagation of interlaminar cracks around the hole. • Back-up use slightly increase the thrust force in drilling of FW GFRP pipes. • In drilling without using back-up, more severe delamination damages occur in the area close to the hole edges owing to intralaminar and interlaminar cracks. • Damage modes were intralaminar cracks, fiber breakages, uncut fibers, and debonding. • Back-up use improves surface quality in drilling FW GFRP pipes.

Analyzing the long-term creep behavior of composite pipes: Developing an alternative scenario of short-term multi-stage loading test

Glass Fiber Reinforced Polymer pipes (GFRP) are used in a variety of industries such as water, oil and gas, aerospace and chemical industries. In the present paper, the creep response of GFRP pipes undergoing compressive transverse loading is analyzed through experimental observations and numerical modeling. Firstly, the long-term creep response of a GFRP pipe is investigated under single-stage loading till more than 400 days. Then, the creep response of another sample from the same pipe is evaluated under multi-stage loading with four 720-h steps (totally 2880 h). Theoretical modeling is performed using a two-level model based on short-term viscoelastic behavior of resin. A procedure is proposed to replace a long-term creep test under a single stage loading with short-term creep tests with multi-stage loading. The proposed procedure is validated through experimental study. The proposed multi-stage creep test scenario is very valuable to reduce the duration of experimental creep test. Utilizing the proposed method during the design process of a GFRP pipe, the creep response of the pipe can be estimated and its long-term properties can be ensured by performing equivalent short-term tests. The proposed procedure is validated through experimental study.

Experimental Evaluation of Internally Pressurized GFRP Pipes Subjected to Vertical Ground Slip

Abstract While glass fiber-reinforced polymer (GFRP) tubes have emerged as a corrosion-resistant alternative to buried steel pipelines, they are not as well understood or widely used. This study ex...

Investigation of the stress-strain constitutive behavior of ±55° filament wound GFRP pipes in compression and tension

The behavior of hollow ±55° filament wound glass fiber-reinforced polymer (GFRP) pipes under longitudinal compressive and tensile loading is studied experimentally using 31 pipe specimens. The main parameters were the nominal pipe pressure rating, namely 350 kPa, 700 kPa and 1050 kPa, and the inner diameter, namely 76 mm and 203 mm. For the compression tests, each specimen was cut to a length of twice the outer diameter and the ends were protected from premature failure using a basalt fiber-reinforced polymer (FRP) wrap. A spherical platen was used to ensure concentric loading. For the tensile tests, a novel test set-up with a specialized gripping mechanism was used to test the full pipe in lieu of the standard coupons extracted from the pipe which suffer from fiber discontinuity, thereby underestimating the strength. The pipes exhibited a nonlinear stress-strain response under both tension and compression loads and exhibited a higher strength in compression than in tension. Additionally, the pipes showed a significant post-peak behavior when loaded in tension. An analytical model capable of representing the behavior of FRPs under axial tension and compression using simplified constitutive relations was adopted and applied. The proposed model captures the nonlinear stress-strain behavior of the hollow pipes in tension and compression as well as the post-peak behavior of the pipes in tension. The effects of fiber angle error are also explored. Understanding the material behavior is important when analyzing these pipes under flexural or axial loading or when analyzing structures using these pipes, such as concrete-filled FRP tubes (CFFTs).

Stochastic fatigue analysis of glass fiber reinforced polymer pipes

The fatigue lifetime of composite pipe subjected to cyclic internal hydrostatic pressure with variable amplitudes is considered. Progressive damage modeling technique is utilized on the basis of stiffness degradation for monitoring damage progress in composite structure. The modeling which consists of three different phases as stress analysis, damage estimation and mechanical properties degradation is implemented in parallel with the random generation of fatigue loading pattern. All involved parameters defining the fatigue loading scheme, including maximum stress amplitude, mean stress amplitude and number of cycles are treated as random variables resembling real conditions of pipes in the operational field. Therefore, instead of deterministic fatigue analysis as a normal practice regulated by normative standards for the experimental analysis, full stochastic fatigue modeling is conducted. Obtained results are statistically analyzed and the probability of each estimated fatigue lifetime is reported.

Experimental Study on Corrosion Resistance of GFRP in High Temperature and High Pressure Acid Environment

In this paper, the corrosion tests of glass fiber reinforced polymer (GFRP) in high temperature and high pressure acid environment were carried out. The surface morphology and glass transition temperature were observed by means of scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and the mechanical property of GFRP was tested. The results indicated that after being exposed to acid corrosion environment, the structure and organization of GFRP changed, and a variety of defects produced on the surface and interior of GFRP, bending strength and tensile strength of GFRP decreased. The surface analysis also proved that there were some etch pits occurred on the GFRP pipes. Furthermore, their barcol hardness became poor.

Preliminary Study on the Acoustic Emission Wave Velocity on Filament Wound Glass Fiber Reinforced Polymer Pipes and its Correspondence with the Winding Angle

In this study, three types of filament wound glass fiber reinforced epoxy composite specimens were tested according to the ASTM standards to evaluate preliminary, the acoustic emission wave velocity. The pipe specimens had 300.0 mm of length, 50.5 mm of diameter and 3.5 mm of wall thickness. Ten points were marked over the imaginary central circle on the pipe middle, from zero degree up to 90º with nine divisions of 10º each one and an additional point representing the crossing of plies. Next, there are positioned two collinear acoustic emission (AE) sensors along the length, positioned at 35 mm from middle, axially. After the specimen preparation, took place the HSU-NIELSEN or pencil lead break (PLB) tests to analyze the signal wave time for both sensors, by means of the 0.3mm – 2H graphite lead brake. The results were compared to considering the angular variation and the velocity for each winding angle. It was evident that the procedure above can determine with good precision the variations occurred on the acoustic emission velocity on filament wound composite pipes, regarding the three angular variations compared. This study was the parameter of control to proceed with the acousticemission evaluation over tensile tests in further studies to predict the fatigue and the damage propagation on this typology of laminates.

Effect of process parameters in surface roughness during turning of GFRP pipes using PCD insert tool

Glass fiber reinforced polymer (GFRP) composite pipes are finding its increased applications in variety of engineering applications such as water softening plants, desalination plants, paper mill industry, marine water treatments. However, the users of FRP are facing difficulties to machine it, because of fiber de-lamination, fiber pull out, short tool life, matrix de-bonding and formation of powder like chips. The present investigation focuses on the effect of process parameters for surface roughness of glass fiber reinforced polymer (GFRP) composite pipes. Experiments were conducted based on the high speed turning centre (CNC) using poly-crystalline diamond (PCD) tool. The process parameters considered were cutting speed, feed, depth of cut, and work piece type (E-Glass mat and E-Glass woven specimen). Both pipes are fabricated using the filament winding process. The pipe consists of 70 percent epoxy polyester resin and 30 percent glass fiber. A comparative study has been undergone between the E-Glass woven and E-Glass mat fiber reinforced composite material. The mechanical properties were also conducted as per ASTM standards. Based on the results, it was observed that good machinability was obtained at lower cutting speed, feed rate, depth of cut for mat fiber reinforced GFRP pipe and at high cutting speed, lower feed rate, depth of cut for mat fiber reinforced GFRP pipe.

On the prediction of long‐term creep‐failure of GRP pipes in aqueous environment

AbstractThe aim of this work was to study the long‐term failure of GRP (Glass fiber‐reinforced Polymer) pipes under the influence of moisture absorption. These pipes are used in water transportation, which has an important effect on the mechanical properties of the polymeric matrix. The GRP pipes are usually tested under ring deflection or internal pressure conditions. This study presents and analyzes experimental creep‐rupture data obtained from standard test methods under ring deflection conditions. This loading configuration simulates in laboratory the conditions verified in a subsoil installation. The creep testing was carried out under constant dead weight on unconditioned and preconditioned samples in a submerged condition. The diametrical deflection of samples was measured periodically, and the time to failure of each sample was recorded. The main purpose of this work was to determine the short and long‐term rupture energies of GRP pipes and assess the influence of moisture preconditioning on those values. The observed failure mode was always the same. It was concluded that the energy at failure decreases with time. The influence of the preconditioning on the creep‐rupture of GRP pipes was considered negligible. Different time‐dependent failure models were described and used for long‐term extrapolation of the experimental data. The maximum strain at failure decreased about 12% from 0.1 to 1,000 hr of creep testing. Furthermore, data extrapolation to 50 years predicts a reduction of strength of about 60%, founded on the most conservative time‐dependent failure criterion. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers

Surface Roughness Parameters Evaluation in Machining GFRP Composites by PCD Tool using Digital Image Processing

Glass fiber reinforced polymer (GFRP) composites find diverse applications in many fields. Their usage in modern automated manufacturing sector demand high quality components and high finish surfaces. As such the present paper makes a study of the surface roughness of the machined surfaces of GFRP composites at different cutting conditions. The GFRP pipes are turned in lathe using Poly-Crystalline Diamond (PCD) tool. During machining, the machined surface images are captured using a Charge Coupled Device (CCD) camera. For all the images average grey scale value (Ga) are calculated. The average grey scale values and surface roughness (Ra) values are correlated and a relation is obtained between them. Also a second order quadratic model is developed for predicting surface roughness in machining of GFRP composites. The results indicate that the developed model can be used to predict the surface roughness of machined GFRP composites. The grey scale values obtained are in good correlation with the surface roughness values measured. The effect of cutting speed, feed, depth of cut and fiber orientation angle on surface roughness is studied and found that feed affects surface roughness, followed by cutting speed and fiber orientation angle. Depth of cut is found to have no effect on surface roughness of machined GFRP composites.

Experimental study on GFRP pipes under axial compression

Fiber reinforced polymer (FRP) is suitable for structures in corrosive environment and long-span lightweight structures due to its high-strength, light-weight, and anti-corrosive qualities. The behavior of pultruded glass fiber reinforced polymer (GFRP) pipes, which are the members of long-span lattice structures, under axial compression was investigated by tests. Short GFRP pipes were first tested to determine the basic mechanical properties. Then the stability of long GFRP pipes was studied by axially compressive tests in four groups with different slenderness ratios, twelve specimens totally. Based on the results of the tests and literature, the formula of the buckling load of composite pipes under axially compressive load was presented based on Perry formula. It can well predict the buckling failure load GFRP pipe under axial compression.

Field Evaluation of a Glass-Fiber Soil Reinforcement System

A soil reinforcement system using the combination of glass-fiber-reinforced polymer (GFRP) pipe and pressure grouting has been developed by a Korean company. The system is being adopted as slope stabilization measures in Hong Kong. Individual GFRP pipes were designed and installed as soil nails with the exception that two-stage pressure grouting was applied instead of gravity grouting. A full-scale field evaluation on constructability and in situ performance of the system was performed in Hong Kong. The performance of the constructed nails was evaluated by pullout tests. The construction procedure, site adaptations of the Korean product made in Hong Kong, field test procedure, and performance of the constructed soil nails are reported in this paper.

Thermo-Mechanical Regulation of Residual Stresses in Polymers and Polymer Composites

Manufacturing processes of polymer and polymer composite products are inevitably linked with buildup of residual stresses which, as a rule, adversely affects the product performance. Mainly used annealing and suitable curing regime may decrease these disapproving effects. Methods of residual stress control in hardened articles using dependence of polymer visco-elastic properties on temperature are considered and some basic features of their efficient application are established. The methods are successfully applied (a) to increase the first crack strain in crossply composite, (b) to enhance "weepage" pressure in glassfiber reinforced polymer pipes and (c) to reduce a central hole influence on ultimate tensile strength in standard polystyrene specimens.