What Size Pvc Pipes Should I Use to Plump My House

Introduction

Plastics are used for a broad range of commercial and industrial piping applications. The most known are polyvinyl chloride (PVC), polyethylene (PE), polypropylene (PP), acrylonitrile–butadiene–styrene (ABS), polybutylene (Lead) and drinking glass–fibre-reinforced polyester (GRP or FRP). Concerning pipe systems for drinking water supply, gas distribution and sewage disposal, PVC, PE and PP are the about pop polymer materials (PlasticsEurope, 2017). Particularly for gravity sewer pipes, PVC has been extensively used over the by decades and has get the dominant construction fabric. Cost efficiency, ease of installation, range of available diameters (xl–630 mm) and its reputed chemical resistance favour its wide acceptance by decision makers in urban drainage (Davidovski, 2016).

Since there are PVC sewer pipes in functioning for at least iv decades, business concern over their longevity has been lately raised in the Netherlands. It is nevertheless unknown whether the expectations of long-lasting PVC pipes (Folkman, 2014) volition prove realistic or new nugget management strategies should be established in the near time to come. Knowledge of the electric current structural integrity of sewer systems is a central consequence for establishing successful asset management strategies, leading to better decision making and more than affordable investments. In practice, sewer managers currently base their strategies mainly on visual (CCTV) inspections (Van Riel, Langeveld, Herder, & Clemens, 2014). Subsequently, decisions are taken whether replacement, rehabilitation or a nearly hereafter inspection should take place. All the same, linking the observed defects in CCTV to the actual physical state of a pipe is challenging (Van Riel, 2017). A necessary condition for achieving this is comprehensive understanding of the mechanisms that affect a PVC piping'south lifetime, their combined effects and eventually their results, which are the defects establish in practice. An overview of these mechanisms and their origins is included in this article. Lifetime prediction methods for plastic pipes are also utilised to describe specific types of failure, while their ability to provide trustful lifetime prediction is discussed.

The principal aim of this article is to present case studies of PVC sewer pipes plant in the literature and to compare the derived conclusions on PVC durability with findings in inspection (CCTV) data. Accent is given on the studies that investigate the properties that define the structural integrity and overall performance of a sewer system. The inspection information concerns three different municipalities in Holland: Almere, Amstelveen and Breda. The primary discrepancies between literature and inspection data are discussed, as a pace towards bridging results from scientific research and observations from do.

Factors and mechanisms affecting PVC pipes lifetime

From the initial stages of production until the last stages of operational lifetime, several factors be which could potentially influence the physical, chemical and, hence, mechanical backdrop of PVC pipes. An overview of these factors and the observed mechanisms is provided in the following sections.

Production

Suspension polymerisation is the most practical procedure for PVC particles product (80%), whereas emulsion and mass polymerisation provide 12 and 8% of the world production, respectively (Fischer, Schmitt, Porth, Allsopp, & Vianello, 2014). Although the specific details of the PVC particles size slightly differ in the literature (Benjamin, 1980; Butters, 1982; Faulkner, 1975), the microstructure follows the same pattern. This can be described in three stages (Butters, 1982): the phase 3-PVC particle (∼100–150 μm), the stage 2-primary particle (∼0.1–2 μm) and the stage I particle (∼10 nm). The conversion of the fabric to a homogeneous product requires that the boundaries of the primary particles disappear and a new continuous entanglement network is developed (Visser, 2009). This procedure is known as the gelation process and its quality is expressed by the gelation level. There are several methods to obtain information nigh the gelation level (Castillo, 2016; Choi, Lynch, Rudin, Teh, & Batiste, 1992; Fillot, Hajji, Gauthier, & Masenelli-Varlot, 2006; Gilbert & Vyvoda, 1981; Gramann, Cruz, & Ralston, 2010; Johansson & Törnell, 1986; Kim, Cotterell, & Mai, 1987; Marshall & Birch, 1982; Real, João, Pimenta, & Diogo, 2018; Terselius, Jansson, & Bystedt, 1981; Van der Heuvel, 1982).

A full general accepted opinion suggests optimum gelation levels of 60–85% (Benjamin, 1980; Breen, 2006). A temperature of >250 °C is needed for this purpose (Guerrero & Keller, 1981), much higher than the deposition temperature of PVC which is ∼205 °C (Wypych, 2015). Due to this fact, thermal energy is complemented with mechanical free energy (high shear stresses) by the use of twin rotating screws, then as to advance this process without extensive exposure of the cloth to high temperatures (Visser, 2009). After, the molten material is introduced in a die so that the final pipe is shaped and cooled. This manufacturing technique is called extrusion and is extensively used to class pipes. Fittings, such as joints, are formed by the injection moulding technique. In the injection moulding process, the melted plastic is injected in a mould, which gives the desired form to the fitting, and after cooling the product is ejected.

During the production process, several additives and fillers may be incorporated in the polymers construction in guild to heighten its chemic and physical properties, respectively. Plasticisers and stabilisers are the main additives as they impact the behaviour and deposition rate of the cloth through its lifecycle. Plasticisers are utilised in guild to replace some monomers of the polymer chain, offering a higher caste of mobility and, hence, more flexibility. For sewer applications unplasticised rigid PVC pipes are used. Stabilisers are added for increased resistance to e.g.: UV rays, chemical attack and other relevant external factors (Cardarelli, 2008). For PVC pipes in Europe, lead has been used until the early 2000s, when it was replaced by calcium-based stabilisers in most countries (Anders, 2014).

Every footstep within the production of PVC pipes and fittings can have an effect on the long-term functioning of the last product. The levels of water and oxygen during polymerisation could influence the formation and quality of the produced PVC particles (Butters, 1982). After, the gelation process, already affected by the degree of polymerisation (Fujiyama & Kondou, 2004), plays a major function in the mechanical properties (Mandell, Darwish, & McGarry, 1982; Moghri, Garmabi, & Akbarian, 2003; Truss, 1985; Van der Heuvel, 1982). These backdrop are determined past the morphology of the material (Benjamin, 1980; Kuriyama, Narisawa, Shina, & Kotaki, 1998) and by the polymer'southward orientation and molecular mobility (Fillot, Hajji, Gauthier, & Masenelli-Varlot, 2007). Additionally, impurities and voids in the polymer structure, oftentimes referred to equally inherent defects, are introduced during production, resulting in crack initiators, and their presence seems to be inevitable (Johansson & Törnell, 1987). The wear observed at the polymer pipes extruders (Gladchenko, Shevelya, Kiyanitsa, & Derkach, 1997) might also contribute to the occurrence of inherent defects.

Residual stresses are also introduced during production, as a result of different cooling rates between the inner and the outer pipe surface (Siegmann, Buchman, & Kenig, 1981), and constitute another parameter that affects the mechanical backdrop of the produced pipe (Siegmann, Buchman, & Kenig, 1982). Relevant inquiry on residue stresses in PVC pipes (Breen, 2006; Meerman, 2008; Scholten, van der Stok, Gerets, Wenzel, & Boege, 2016) has revealed that their magnitude is in a range of 0.9–four.8 MPa for tensile and 3.9–nine.4 for compressive stresses (Table 1). In principle, a faster cooling charge per unit or a thicker pipage wall thickness will atomic number 82 to higher levels of residue stresses (Janson, 2003; Scholten et al., 2016). However, irrespective of their magnitude, residual stresses touch on the crack propagation equally they change the stress profile through the pipe (Burn down, 1992; Chaoui, Chudnovsky, & Moet, 1987), increase the breakable–ductile temperature (Scholten et al., 2016), and, consequently, they seem to have a tremendous effect on the lifetime of pressurised plastic pipes (Hutař et al., 2013; Poduška et al., 2016).

A review on the durability of PVC sewer pipes: enquiry vs. practice

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Tabular array i. Observed values for circumferential remainder stresses in PVC pipes.

In the literature, the residual stresses in plastic pipes have been estimated by solely slitting pipe rings approaches and measuring the change in perimetry (Breen, 2006; Janson, 2003; Meerman, 2008), or slitting is combined with layer removal methodologies (Doshi, 1989; Poduška et al., 2014, 2016; Williams, Hodgkinson, & Gray, 1981) in lodge to acquire a more accurate distribution of the remainder stresses through the pipe thickness.

The values of remainder stresses listed in Table ane are estimated based on Equation (1) for tensile residue stresses (Breen, 2006) and Equation (2) for compressive residual stresses (Janson, 2003): (1) $$\sigma =\frac{l_o·d}{4·\pi ·R^2}·E$$ (1) where $l_o$ is the overlap length, $d$ is the wall thickness, $R$ is the mean radius of the pipage wall and $\mathrm{East}$ is the modulus of elasticity: (2) $$\sigma =\frac{a}{\pi ·D_{\mathrm{yard}}-a}·\frac{s}{D_m}·\mathrm{East}$$ (2) where $a$ is the reduction of the pipage perimetry, $\mathrm{southward}$ is the piping wall thickness, $D_{\mathrm{thousand}}$ is the hateful pipage diameter and $E$ is the pitter-patter or relaxation modulus of the pipe. The description of Eastward modulus in the equations of this commodity is kept as in the original sources. Still, in viscoelastic materials (a.o. PVC), E is described as creep or relaxation modulus, since it is a function of loading time.

Installation

The conventional installation procedure involves the digging of an open trench, lying of the pipe and soil roofing and compaction. Yet, during transport and installation of plastic pipes, scratches and dents can exist inflicted on the pipage surface. These plastic deformations can afterward deed as stress risers, and under certain service atmospheric condition can eventually pb to failure. Improper soil compaction is as well the crusade of pipe ovalisation, resulting in high tensile stresses at the 12 and 6 o' clock positions of the inner surface and at the iii and 9 o' clock positions of the outer surface. In pressurised systems, homogeneous soil embedding tin exert external pressure on the piping, counteracting the internal pressure and hence reducing the probability of crack germination (Hutař et al., 2011).

Additionally, poor quality of soil embedding could dilate the effects of the low bending stiffness institute in plastic pipes, resulting in improper and challenging to measure longitudinal slopes in gravity systems, and in pre-buckling conditions (Stein, 2001). Another gene that can touch the material degradation is determined by the conditions of storage prior to installation. Photochemical deposition caused past UV rays has been proven to be harmful for the mechanical backdrop of PVC pipes (Anton-Prinet, Mur, Gay, Audouin, & Verdu, 1999; Hussain, Hamid, & Khan, 1995).

Performance

During operation, four main ageing mechanisms have been identified: physical ageing, mechanical degradation, chemical deposition and environmental stress cracking (ESC). Physical ageing in polymers is a phenomenon which imposes changes on a textile'south property as a function of time, at a constant temperature and independently of other external factors (Hutchinson, 1995). Amorphous (or glassy) polymers, such as PVC, experience physical ageing due to the fact that they are cooled to a temperature below their glass transition temperature (T_grand ), and, hence, are not in a thermodynamic equilibrium state. In this non-equilibrium state, the glassy polymer has excessive thermodynamic properties and there is a continuous effort to reach the equilibrium state (Hutchinson, 1995). Physical ageing can be traced by reduction in book and enthalpy, but besides by changes in the mechanical properties (Rabinovitch & Summers, 1992). The polymer becomes stiffer and more breakable, whereas its creep and stress relaxation rates decrease (Laiarinandrasana, Gaudichet, Oberti, & Devilliers, 2011; Struik, 1977). In principle, physical ageing is an inevitable, although reversible (Hutchinson, 1995), process in polymers which is accelerated at higher temperatures (Visser, Bor, Wolters, Warnet, & Govaert, 2011).

Mechanical degradation is the outcome of stresses which are exerted on the piping (or joint) and their level surpasses the material'southward fracture threshold. It appears in the class of fissures (crazes, cracks) or breaks. Stresses originate from internal pressure, deflections due to soil cover, and the production procedure (residual stresses). Additional stresses tin can be imposed by centric bending due to improper soil bedding and compaction. The quality of pipe extrusion tin be a decisive factor for the longevity of the pipe, as scissure initiation is observed in built-in voids and impurities. Subsequently, the propagation of the crevice is governed by the magnitude and direction of the applied stresses. This failure machinery is known as Irksome Fissure Growth (SCG). In case of external impacts (e.chiliad. striking by an excavator), mechanical deposition could surface as rapid crevice propagation. Autonomously from processing quality, temperature is as well a critical factor concerning the mechanical backdrop of the fabric. Lower temperatures result in more brittle failures, whereas the amount of energy that can be captivated by PVC pipes before fracture seems to reduce dramatically (McGarry, Mandell, & Hsueh‐Lee, 1985; Scholten et al., 2016; Visser et al., 2011).

Chemical degradation involves the occurrence of chemical reactions between the polymer pipe and the environment, leading to breakage of the polymer covalent bonds. The covalent bonds build up the main back bone of a polymer chain, hence their breakage results in chain scission and molecular weight reduction. Dehydrochlorination (HCl abstraction) is often the cause that commences chemical deposition in PVC (Breen, 2006), due to the creation of sequential conjugated polyenes (Arnold, 2003), which is also the source of the discolourisation appearance. The impact on the mechanical backdrop has been characterised with the term 'stress corrosion cracking', and is realised in four stages (Choi et al., 2005): initiation of microcracks, slow cleft growth, clustering of cracks and clusters growth.

Environmental stress cracking is a failure mechanism very like to slow crack growth in terms of shape. Information technology is a physical procedure driven by the applied stress but accelerated by the presence of an active surround (Bishop, Isaac, Hinksman, & Morrissey, 2000), as diffusion is the factor that enhances the susceptibility to fractures due to the creation of plasticised (softer) layers and surface energy reduction (Arnold, 2003). Breen (1993, 1994, 1995) has explored crazing and crevice growth mechanisms concerning PVC pipes in vapour and liquid environments, concluding that above a sure level of surround concentration and stress intensity, the material'south load-bearing capacity tin subtract. In general, a broad range of glassy polymers (including PVC) has been investigated regarding their ESC resistance under various types of environments (Robeson, 2013), indicating that issues of ESC may appear in sure combinations of 'material-surroundings'.

Lifetime prediction methods and their limitations

Hydrostatic testing and standard extrapolation method

A conventional way of rating a thermoplastic piping is past determining the resistance to constant internal pressure, as it is described in ISO 1167-one (2006). The experiments are implemented under several internal pressures and temperatures, and under certain environmental weather (i.e. water in water, h2o in air, water in liquid). The time to failure is recorded and the results are depicted as a double logarithmic σ_hoop vs. t _failure curve. An incident of failure is considered when at that place is leak or interruption. The type of failure can be ductile (Region I), quasi-brittle (Region II) or brittle (Region III).

Figure 1 shows how the level of applied stress leads to one of the three types of failure every bit a function of fourth dimension. In case of high stress values (Region I), a yield deformation in the failure zone is vivid with fracture appearing within curt testing times. For intermediate stress levels (Region Ii), the failure is generated in longer testing times and is characterised by slow crack growth with local plastic deformation only at the fissure front. In even longer testing durations (Region III), there is no apparent yield deformation and the occurrence of fractures is most independent of the stress level. The points of transition from Region I to II and from II to III are frequently referred to every bit the 'mechanical knee' and the 'chemical knee', respectively.

A review on the immovability of PVC sewer pipes: research vs. practice

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Figure i. The types of failures observed in thermoplastic pipes subjected to various levels of hoop stress.

Figure 1. The types of failures observed in thermoplastic pipes subjected to diverse levels of hoop stress.

College testing temperatures tend to motion the curves to lower failure times, assuasive for shortest testing periods. This is apparent in Figure ii, in which the maximum level of hoop stress as a office of fourth dimension and temperature is presented for unplasticised PVC pipes. Extrapolation to service temperatures tin and so be performed according to the standard extrapolation method (SEM) published in ISO 9080 (2012). Standard extrapolation method requires all-encompassing hydrostatic testing at two or more testing temperatures (>30 samples per temperature) and the application of certain statistical methods to the obtained experimental data sets.

A review on the durability of PVC sewer pipes: inquiry vs. do

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Figure 2. Maximum hoop stress (MPa) with respect to time (hours) for diverse temperatures concerning PVC-U pipes. Data is retrieved from Kunststoffrohrverband (1997).

Figure 2. Maximum hoop stress (MPa) with respect to fourth dimension (hours) for diverse temperatures concerning PVC-U pipes. Data is retrieved from Kunststoffrohrverband (1997).

1 apparent limitation of performing hydrostatic pressure tests is the necessary duration of the experiments. The relevant standardised guidelines (ISO 1167-i, 2006; ISO 9080, 2012) bespeak that the applied internal pressures should be at such levels that at to the lowest degree four specimens would fail later on 7000 h (292 days) and at least ane after 9000 h (375 days). This fact could justify that this kind of method has been used but by a few researchers and usually partially, in order to avoid the extensive testing required by SEM. A case of full implementation of this method has been published by Krishnaswamy (2005), who tested eight different kinds of HDPE piping resins. Other reported limitations originate from the thermal ageing involved in this method. Sorption and diffusion of oxygen or other chemicals in the polymer matrix are temperature-dependent micro-mechanisms contributing to the failure process (Lang, Stern, & Doerner, 1997). Still, SEM lacks in incorporating the variability of dissimilar temperature-dependent rates introduced by dissimilar concrete and chemical processes.

Arrhenius equation

Application of the Arrhenius equation is considered feasible under the assumption that the deposition rate of the material follows a first-society kinetics. It is a method highly connected with the chemical aspects involved in the degradation process, indicating the depletion of the introduced stabilisers and the onset of thermo-oxidative deposition (Figure ane, Region III). These aspects are usually expressed via the reduction of the oxidation consecration time or the build-up of hydroperoxides (ROOH).

The concept backside this method is also higher testing temperatures and shorter testing periods. Later on, the Arrhenius model is used for extrapolation of the rate of degradation reaction (k) to other (service) temperatures, allowing for lifetime prediction: (3) $$\ln \mathrm{1000}=-\frac{E_{\mathrm{a}}}{R}\frac{\mathrm{one}}{T}+\ln C$$ (3) where m is the degradation reaction charge per unit, E_a is the activation energy of the reaction (kJ/mol), R is the gas abiding (8.31 JK^–onemol^–1), T is the testing temperature (One thousand) and C is a constant.

The assumed linearity involved in the Arrhenius model seems, however, to be valid just for a range of testing temperatures (Celina, Gillen, & Assink, 2005). This fact indicates that circumspection should also be exercised for the use of the extrapolation factors k_e which are included in ISO 9080 and concern lifetime prediction in instance of Region III failure based on the Arrhenius linearity. For case, relevant research on PP (Celina et al., 2005) has shown that at circa lxxx °C the degradation rate of PP seems to lose its Arrhenius linearity. Generally, thermo-oxidative degradation based on accelerated ageing experiments is a more complicated mechanism that depends on the physics involved in the process (e.g. diffusion), and the behaviour of the present stabilisers and other additives (Celina, 2013).

Linear elastic fracture mechanics

Numerous researchers have focused on simulating slow crack growth (Figure 1, Region II) which originates from inherent flaws and is propagated past the applied stresses. The applied stresses are expressed via the stress intensity gene K_I , which considers the internal pressure, the pipe and scissure geometrical characteristics, and the blazon of loading (Maiti, 2015). K_I corresponds to the mode I blazon of loading which indicates tension of the piping in a direction perpendicular to the airplane of the crack.

The time of crevice initiation can be expressed via (Lang et al., 1997): (4) $$t_{in}=B·K_I^{-n}$$ (4)

Every bit shown in Figure 3, when the fissure growth rate da/dt (or å) is plotted against the stress intensity factor K_I in a double logarithmic scale, Equation (5) can be established for a specific range of da/dt in order to describe tiresome scissure growth. Prior to this stage, crack growth rate decreases rapidly as the threshold value K_{I th} is approached, whereas at the end it increases apace as the textile'south fracture toughness K _IC is approached: (5) $$\frac{da}{dt}=A·K_I^{\mathrm{thou}}$$ (five)

A review on the durability of PVC sewer pipes: research vs. practice

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Effigy 3. Creep crack growth rate every bit a part of stress intensity factor K_I .

Figure iii. Creep crack growth rate as a role of stress intensity factor K_I .

B, n and A, m used in Equations (4) and (5), respectively, are sets of constants which depend on the tested material.

The lifetime prediction tin exist accomplished by estimating the crack initiation time co-ordinate to Equation (4) and integrating Equation (5) for the stable cleft growth catamenia: (half-dozen) $$t_f=t_{in}+t_{\mathit{SCG}}=B·K_I^{-\mathrm{north}}+{\int }_{a_o}^{a_f}\frac{da}{A·{\left({\mathrm{Chiliad}}_I\right)}^m}$$ (six) where a_o is the assumed initial flaw size and a_f is the critical fissure size which is ordinarily assumed to be the pipe wall thickness. Most of the authors, yet, tend to neglect the initiation time t _in equally carve up experiments are needed for the decision of B and n, and it is considered negligible compared to the magnitude of t _SCG.

This lifetime prediction model has been the basis for extensive research on PE pipes (Deveci & Fang, 2017; Frank, Freimann, Pinter, & Lang, 2009; Frank, Hutař, & Pinter, 2012; Kratochvilla, Frank, & Pinter, 2014; Pinter, Lang, & Haager, 2007; Wee & Choi, 2016; Zhao, Choi, & Chudnovsky, 2013), PVC pipes (Balika & Lang, 2002; Gould, Davis, Beale, & Marlow, 2013) and elastomers (Arbeiter, Schrittesser, Frank, Berer, & Pinter, 2015). The types of specimens used in such experiments are usually the cracked round bars or circular notched specimens. Other types of experiments include specimens for the Pennsylvania notched exam (Brown, 2007; Nezbedová et al., 2013; Robledo, Domínguez, & García-Muñoz, 2017) and the strain hardening exam (Deveci & Fang, 2017; Robledo et al., 2017).

Linear elastic fracture mechanics (LEFM) method is based on brusque-term (mainly fatigue) tests and focuses on describing the fracture mechanisms (i.eastward. slow crack growth) at the crack tip. This fact implies that other types of degradation, such equally chemical, which may occur in a plastic pipage should be restricted in the area of the crack tip. Otherwise, tedious crack growth is no longer the disquisitional factor for the pipe's failure, and the application of the LEFM method in its conventional class seems to be invalid. Another limitation in applying the LEFM method is the requirement for input of the precise geometry (size and shape) of the initial defect. Analysis of the uncertainties that are introduced in modeling tedious crack growth by means of LEFM for PVC (Davis, Burn down, Moglia, & Gould, 2007) and HDPE (Khelif, Chateauneuf, & Chaoui, 2007) emphasised the significance of inherent defect sizes in the reliability of the model's event. Other researchers (Burn, 1991; Lu, Davis, & Burn, 2003) have as well commented on the sensitivity of the estimated lifetime prediction to the initial flaw geometry. Co-ordinate to the literature, initial defect sizes of 100–400 μm seem to be realistic (Lang et al., 1997).

Quality number

The quality number method was applied for plastic pipes solely by Whittle and Tennakoon (2005), co-ordinate to the authors' knowledge. Information technology considers the properties that affect the immovability of the system and their corresponding weighting factors in a cumulative form (Equation (7)). Lifetime prediction is made past applying Equation (7) on several pipes of different ages and creating a simple linear regression with the piping age as the independent variable. Later on, extrapolation is viable to longer ages until a threshold quality number is reached, below which a pipe is considered to be dangerous for further operation. The age which corresponds at the threshold is considered as the predicted lifetime: (7) $$Q=\sum _{i=1}^n{\mathrm{Westward}}_i\frac{M_i}{R_i}$$ (seven) where Q is the total quality number, Due west_i is the weighting cistron of a property, M_i is the measured value of a property and R_i the reference value of a property.

It is reasonable to land that the results obtained by this method are certainly open to dispute. This is due to the fact that the upshot is dependent on the arbitrary choice of the weighting factors and the threshold quality number, rising the levels of dubiousness. Additional caution should also be exercised when applying this method every bit it implies a connexion between the age and the integrity of the pipe, irrespective of the quality of product. However, older pipes which are more than well candy than newer pipes could provide college values of Q, leading to a regression model with positive gradient. This fact would result in the poorly founded conclusion that failure will never occur.

PVC pipes in literature

Material properties

A moderate corporeality of inquiry is published concerning PVC sewer pipes, which are either new or used for several years, and have been utilised in different areas. Table 2 provides an overview of specifications of the tested exhumed pipes. An early report (Bauer, 1990) was conducted on a 15-year one-time PVC sewer pipe (DN 254, SDR 35) in Dallas, Texas, based on the requirements imposed by ASTM D 3034. Measurements of the tensile backdrop showed a mean tensile strength of 52.36 MPa and mean modulus of 2839 MPa in the circumferential direction and 55.iv and 3059 MPa, respectively, in the longitudinal direction. The boilerplate pipe stiffness was reported to be 433 kPa according to ASTM D 2412-11. A serial of other tests following the respective American standards took place, including extrusion and installation quality, dimensions measurement, impact resistance and flattening resistance. According to the study, the results revealed that all the measured properties comply with ASTM D 3034 and no observable degradation had occurred.

A review on the immovability of PVC sewer pipes: research vs. practice

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Table ii. Overview of tested PVC sewer pipes.

Similar studies in Europe (Alferink, Guldback, & Grootook, 1995; Meerman, 2008) include the investigation of several PVC sewer pipes of dissimilar SDRs and ages (Tabular array 2). A lot of emphasis has been given to deflection measurements and production or installation practices. Withal, there is no extensive exploration of mechanical backdrop and their potential deterioration. The only case concerns two PVC pipes from Norway (Notteroy) and Sweden (Torshalla), whose backdrop have been compared with a brand-new pipe. The results (Table 3) bespeak that the properties of the pipes have been compromised. The pipe tested from Kingdom of norway, which is of the same diameter merely of lower pipage wall thickness (higher SDR value) compared to the reference piping, betoken only a slight decrease of xvi.viii% in strain at suspension, whereas the yield stress remains intact. Concerning the pipe from Sweden, the results revealed a 7.8% subtract in yield stress and 80.vi% decrease in strain at break, a fact which may be explained by the depression degree of gelation. A contributing factor to the decrease in the strain at interruption is also concrete ageing although an increase in yield stresses was expected.

A review on the durability of PVC sewer pipes: inquiry vs. practice

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Table three. Material properties of ten PVC sewer pipes in French republic, Denmark and Kingdom of norway (Alferink et al., 1995).

In this study, the degree of gelation was expressed as a pct of assault of methylene on PVC. Based on the provided values for all pipes, information technology is obvious that the bulk of the pipes seem to be of poor production quality, i.e. low degree of gelation. In the netherlands the case of seven exhumed PVC sewer pipes has been reported (Meerman, 2008). The level of degradation of these pipes was evaluated based on visual and microscopic inspection, geometrical analysis and surface roughness measurements (Table 4). Comprehensive testing on the pipage'southward backdrop did not accept place, and the suggestion of at least 100 years lifetime was based on a previous report on PVC water pipes (Breen, 2006). It has to exist realised that in drinking water pipes the environment is totally unlike and chemical degradation or ESC as failure machinery is neglected.

A review on the immovability of PVC sewer pipes: research vs. exercise

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Tabular array 4. Material properties of vii PVC sewer pipes in the Netherlands (Meerman, 2008).

The results of a more comprehensive, in terms of mechanical backdrop, study (Whittle & Tennakoon, 2005) of seven PVC sewer pipes that had served for up to 25 years in Australia are summarised in Table 5. These properties were also combined with the production procedure conditions. In this case study, the caste of gelation is expressed every bit the gelation level, determined by ways of differential scanning calorimetry. Every bit it is indicated by the results, at that place is no bodily connection between the age, the gelation level and the mechanical properties of the tested pipes. In fact, the pipage with the lowest gelation level (35%) correspond to the highest magnitudes of stress (39.3 MPa) and elongation (117.2%) at break. At the aforementioned fourth dimension, pipes with optimum gelation levels (76–88%) correspond to the lowest magnitudes of yield stress and tensile forcefulness. A valid argument provided past the researchers of this study is that higher concentrations of fillers, expressed every bit an increase in specific gravity (i.due east. from 1.465 for DN 150 to ane.522 for DN 225) could have led to this discrepancy. Finally, application of the quality number method (Equation (v)) yields proposed lifetimes of 98–288 years based on a worst-instance and all-time-case scenario, respectively.

A review on the immovability of PVC sewer pipes: enquiry vs. practice

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08 October 2019

Table v. Fabric properties of 7 PVC SDR38 sewer pipes in Australia (Whittle & Tennakoon, 2005).

Pipe stiffness is considered as the main design belongings in gravity sewer pipes. This fact has led some research approaches to focus on the mechanisms and properties of plastic sewers which are considered to exist connected with pipage stiffness, such as deflection and stress relaxation. The deflection of a flexible pipage is a part of several parameters. Pipe material and geometrical characteristics, the bedding and backfilling material, the compaction degree, the burial depth and the beingness of geogrid reinforcement could alter the levels of deflections significantly (Hsieh, Wu, & Huang, 2010; Mohamedzein & Al-Aghbari, 2016; Välimaa, 1982). Irrespective of potential structural deterioration, piping deflections in sewer pipes have a profound impact on pregnant operational and asset direction aspects, such as the flow government (Stein, 2001) and the toll of future trenchless rehabilitation (Kuliczkowska, 2014) respectively.

The results of deflection measuring programmes regarding PVC sewer pipes in several countries are summarised in Tabular array A1. In Europe, deformations of up to 14% were observed (Alferink et al., 1995; Välimaa, 1982; Walton & Elzink, 1989). The magnitudes of these values are in accordance with the values observed in the United states (Moser, Shupe, & Bishop, 1990). Observation of the temporal alterations of these values with respect to fourth dimension since installation justifies that ninety–95% of full deflection is realised within the first two years (Joekes & Elzink, 1985). This period is besides considered sufficient to account for soil consolidation due to groundwater fluctuations (Moser et al., 1990). In-situ deflection measurements reported past Kuliczkowska (2014) on approximately three.five km of newly layed PVC sewer pipes of several diameters (200–500 mm) confirm that similar deflection values (upwardly to 15%) tin can be obtained even at the offset stages after installation, whereas the vast majority of the tested pipes (95%) were subjected to deflections between two and x%. Other research (Alferink et al., 1995) has also highlighted the importance of installation quality. Moderate installation yields magnitudes of hateful deflection up to 5.5%, whereas poor installation results in hateful deflections of up to xiii% and maximum deflections upward to xx.5%.

The impact of pipe stiffness (expressed as SDR) on the performance of an operating pipe has been explored (Välimaa, 1982) via an elaborated field exam of six PVC pipes with variations in pipage stiffness, soil cover and compaction method. By the end of the testing menses (i.e. seven.5 years), at which the deflection levels are considered to be stable, soil embrace appears to exist the near dominant factor (Table 6). At 1.two m depth, the pipage of lower pipe stiffness with better soil compaction was less deflected than the pipe of higher stiffness. At 0.6 m depth pipe stiffness played a more significant role than the compaction method. Hence, pipe stiffness seems to exist more important in depression depths, whereas in high soil covers the compaction method becomes more than pregnant.

A review on the durability of PVC sewer pipes: inquiry vs. practise

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08 October 2019

Table half-dozen. Guess deflection values of PVC sewer pipes 7.five years after installation as a office of SDR, compaction quality and soil cover (Välimaa, 1982).

Stress relaxation in PVC sewer pipes has been extensively studied by Struik (1977) and Janson (1988, 1995, 2003). Information technology is proved that under abiding deflection, stress decreases implying that modulus Eastward decreases. Viscoelasticity causes a stress relaxation land which indicates that if failure does not occur during the initial loading, it is very unlike that failure in the long term volition occur as the practical stress volition continuously decline.

However, this decrease in the modulus should non be translated as a decline in the force of the pipe as the brusque-term value of the modulus remains intact, or is even enhanced equally a result of physical ageing (Janson, 1995, 2003). This has generated a confusion amidst researchers as to whether the long-term (Hsieh et al., 2010; Janson, 1988; Koski, 1982) or short-term (Janson, 1995, 2003; Moser et al., 1990) value of modulus should be used to depict pipage stiffness (Equation (12)). Janson (1995) argues that whether the brusque-term or long-term stiffness should exist considered depends on the blazon of soil and the impact information technology has on the behaviour of the pipe. Therefore, for sandy soils the use of brusk-term stiffness is appropriate, whereas for plastic soils the long-term stiffness is. Concerning this dispute, Moser et al. (1990) presented the results of the pipe stiffness of PVC pipe samples that had been constantly strained for 13 years under testing conditions. The pipe stiffness was determined after 1 h of the initial imposed deflection (5 and 25%), and was compared to the pipage stiffness measured after 13 years by imposing additional deflection of 5%. The pipes proved to be capable of withstanding additional deflections, which is in accord with the last findings of Janson (2003). Finally, the influence of fillers and notches on pipe stiffness has as well been investigated (Moser et al., 1990), but hardly any significant differences appeared compared to the united nations-notched or unfilled segments, respectively.

The vast majority of research in the literature concerns plastic sewer pipes that operate under gravity in which the applied stresses are limited to the outcome of piping–soil interactions. In contrast, in that location is a scarcity on research regarding pressurised plastic sewer systems. Co-ordinate to the authors' knowledge, but 2 such case studies have been reported (Folkman, 2014; Gould et al., 2013). Therefore, cases of conducted research on pressurised PVC pipes for other applications, which could apply for sewer systems, are also addressed time to come. At this point, it has to be stressed that the operation of sewer pressurised systems is not governed by a steady internal pressure (creep) as in gas and h2o systems, just by a circadian pressure blueprint (fatigue). However, the failure mechanism of tedious crack growth remains the same in both cases (Hu, Summers, Hiltner, & Baer, 2003).

A recent investigation (Folkman, 2014) of a 20-year-erstwhile pressurised PVC sewer pipe took place in the The states. The pipe successfully passed the tests of hydrostatic integrity and acetone immersion. A more detailed written report on a failed 34 years erstwhile ascension chief sewer PVC pipe in Australia has been published (Gould et al., 2013). In guild to appraise the failure cause, a serial of methods based on micro-scale examination (SEM) and fractography (FT-IR and EDS) take been practical. The determination was that an inherent inclusion created during the manufacturing procedure served as a stress riser and resulted in crack initiation and eventual failure. In fact, EDS during SEM indicated that iron (Fe) elements were found in the revealed inclusions, implying a low-quality manufacturing procedure. However, no material deposition due to the contact with sewage was detected although the scissure seems to have initiated in the expanse of the pipe where discolorisation is most profound.

Apart from inherent defects, notches caused during installation could also bear upon the performance of the piping. Towards this direction, Burn (1991) explored the effect of notches on PVC pipes which are subjected to cyclic pressure. The experiments included PVC pipes of certain specifications (DN110, grade 20, Every bit 2977) tested at a circadian pressure of 1.2 ± 0.3 MPa at a frequency of 0.5 Hz. The results revealed that notch depths higher up a certain level could reduce the lifetime of a pipage drastically. For the given pipe, a notch of >one.2 mm increases the failure probability when subjected to 1.vii million cycles (resembling 100 years lifetime for Australian operating weather condition).

Finally, the response of thermoplastic pipes (including PVC) under two cases of combined loading has been investigated (Alferink, Janson, & Wolters, 2004); i) internal force per unit area and deflection and ii) internal force per unit area and centric bending. The results revealed that external loads in fact heighten the performance of the pressurised pipe and the bending stresses relax in fourth dimension. All the same, failure due to excessive axial bending has been recorded (Broutman, Duvall, & And then, 1990) apropos ii PVC (SDR 26) h2o pipes.

Chemic resistance

The materials used for the production of thermoplastic pipes, which are destined for fluid conveyance applications, are generally considered every bit chemically resistant. Especially, PVC is thought to be the most resistant material against both chemical degradation and chafe, a fact which explains its massive use in sewer systems. An important issue for both drinking and wastewater plastic pipes is the existence of certain disinfectants in drinking water. Their influence on PVC pipes was studied extensively by Fumire (2008). Static tensile and dehydrochlorination tests, combined past molecular weight measurements and SEM examinations, took identify earlier and after exposure to some common water disinfectants, i.eastward., sodium hypochlorine–dichlorine (NaClO–Cl_two) and chlorine dioxide (ClO₂). Even concentrations of 8 ppm of such disinfectants at 40 °C did not manage to impose pregnant changes on the material. Indeed, co-ordinate to other studies (Kowalska, Klepka, & Kowalski, 2016; Kowalska, Rudawska, & Kowalski, 2014), the added chlorine atoms that derive from chlorinated water are considered as a possible reason for a slight increase in the mechanical backdrop of PVC.

Similar studies have been published for the performance of polyethylene pipes against chlorine-based solutions (Castagnetti, Mammano, & Dragoni, 2011; Ghabeche, Alimi, & Chaoui, 2015; Hassinen, Lundbäck, Ifwarson, & Gedde, 2004; Yu et al., 2011). In these cases, the amorphous part of polyethylene proved to be very sensitive particularly to chlorine dioxide and muriatic acid, followed past rapid depletion of antioxidants and an increase in crystallinity. The issue of the mentioned studies indicates the overall superiority of PVC over PE concerning chemical resistance to oftentimes utilised disinfectants. This tendency comes partially in contrast with the findings of the comparative inquiry conducted past Kowalska et al. (2016), as chemical changes at the material surface seem to be more profound in PVC than HDPE pipes, albeit the mechanical backdrop are non affected in both materials.

Earlier relevant research on PVC also confirmed its chemical resistance. Bishop (1990) introduced a test method for estimating the pipe stiffness of PVC samples, while subjected to constant deflections of 5–10%, and 5% concentration of sulphuric acid (H₂Then₄) or sodium hydroxide (NaOH). Subsequently testing periods of more than 1 yr, the results revealed negligible effects on the pipe stiffness. The resistance of PVC against sulphuric acrid was as well verified in some other study (Hawkins & Mass, 1994), in which calcium carbonate (CaCO_three)-filled PVC sewer pipes were investigated by means of SEM and wavelength dispersive Ten-ray (WDS) analysis. The pipe samples were exposed to H₂SO₄ (20%) for testing periods up to six months. The PVC matrix proved to be very resistant as CaCO_three reacted with H₂SO₄ only at the surface of the material.

Finally, a comparative enquiry on the chemical resistance of PVC, PE and PP to sulphuric acid and sodium sulphate (Na₂SO₄) at 25 and 40 °C has been published (Lasfar et al., 2014). The research included measurements of the tensile strength and elongation at break for several durations of immersion. According to the results (Table 7), tensile force was enhanced whereas the elongation at suspension was reduced, implying an increase in crystallinity and diffusion of the environment in the material, merely no chemic degradation.

A review on the durability of PVC sewer pipes: research vs. practice

Published online:

08 Oct 2019

Table 7. Tensile force and elongation at break of PVC specimens aged in H₂SO₄ (Lasfar et al., 2014).

Elastomeric joints

There are several types of thermoplastic pipes jointing, including mechanical and welding techniques (Headford, 1998; Stokes, 1989). The virtually common types of joints in sewer systems are the push-fit, i.e. bell and spigot, and double socket joints. Developments of the conventional push button-fit joints tin can exist establish, such as the Rieber articulation (Magnusson, 1982; Rahman & Bird, 2006).

Some researchers accept focused exclusively on the functioning of the joints in plastic pipe systems. Meijering, Wolters, and Hermkens (2004) studied double socket joints that had been for upwardly to 30 years in service of PVC gas-distribution systems. The assessment of the joints condition was made based on leak tightness testing under deflection, compression set estimation and determination of basic mechanical backdrop. Leakage was observed only for piping deflections over 36%, whereas in 1 case the critical deflection reached the level of 81% (Tabular array 8). The compression ready was measured in an estimate range between 15 and 50%.

A review on the durability of PVC sewer pipes: inquiry vs. practice

Published online:

08 October 2019

Table 8. Critical deflection values that commenced leakage under testing (Meijering et al., 2004).

Arsénio (2013) also concluded that only extreme bending angles (above x°) or consummate pull-off of the pipe could lead to leakage at the joints regarding drinking water systems. In terms of leak tightness in elastomeric joints, the failure modes that can be observed in push-fit joints are listed and described in detail in Arsénio, Vreeburg, Pieterse-Quirijns, and Rosenthal (2009). Namely, these are joint bending, vertical deportation, horizontal displacement, pipage angle, axial displacement, torsion by slight rotation/vibration and pipe ovalisation. The standardised methods and conditions used to test the leak tightness of joints in gravity menstruum applications are presented in NEN 1277 (2003), and are discussed and assessed by García, Cortés-Pérez, and Moore (2016).

Bauer (1990) and Meerman (2008) commented on the excessively good quality of the elastomeric seals of exhumed PVC sewer pipes (Table 2), admitting their conclusions were drawn simply by visual inspection. In the mentioned studies, the effects of potential microbiological assail on the sealing cloth have non been investigated. Other researchers have focused on the functioning of elastomeric joints towards root intrusion, considering the interfacial pressure level as a disquisitional factor. Whittle and Tennakoon (2005) investigated the interface pressure of seven PVC sewer pipes and information technology was concluded that merely two comply with the requirements provided past the relative Australian Standards (AS 1260-1984) and Chase (1979), which recommend force per unit area interface higher than 0.55 MPa for vii mm of continuous width.

Similarly, Sadler, Burn down, and Whittle (2001) tested 22 joints (slip-coupling and lip-seal) used in PVC sewer pipes. After 29 months of accelerated root intrusion testing, it was concluded that for interfacial pressures of 0.04–0.xx MPa, root intrusion is likely to occur, but the values of interfacial pressures suggested by AS 1260-1984 are very restrictive and could lead to ring removal and installation difficulties. The detailed experimental setup is described in Lu, Burn, and Whittle (2000), which includes preliminary tests regarding elastomeric joints of PVC, vitrified dirt (VC) and fibre-reinforced concrete (FRC) pipes.

The superiority of PVC compared to VC and FRC was finally reported past Whittle (2003), claiming that the surface roughness and porosity of the latter materials were the principal crusade of root intrusion through the sealing joints. Scharwächter (2001) also assessed the magnitude of sealing forces that must exist applied for achieving long-term tight joints in non-pressure systems. Past applying method 4 of WG13 (TC 155/CEN), it was ended that a long-term (because the relaxation of the elastomer) sealing forcefulness of iii–4 N/mm (compression set ∼25–30%) seems to be sufficient.

The performance of bell and spigot joints of PVC with respect to the burial depth, the bedding weather and the loading position has also been studied (García & Moore, 2013). The results revealed that several problems may arise (vertical deformations, changes in pipage diameter, rotation and shear forces) but the leak tightness of the joints under the imposed atmospheric condition was non assessed. Balkaya and Moore (2009) investigated the interaction between a Rieber-type PVC gasket and the piping with the means of finite elements modelling (FEM). The results from the analyses revealed that the friction coefficient affects the stiffness of the joint and that increased gasket modulus leads to increased insertion force and bending moment. In a afterward publication (Balkaya, Moore, & Sağlamer, 2012), the same model was studied in order to test the bell and spigot-jointed PVC water pipes that lie on non-uniform bedding, which was simulated by voids of different sizes. The conclusions derived by FEM included higher deformations in the case of improper bedding under the joint and lower deformations in the case of stiffer soils around the pipes.

PVC pipes in practice

Inspection (CCTV) data from two Dutch municipalities (Almere and Breda) indicates that plastic pipes are used extensively (∼l% of each organisation) for urban drainage purposes. Polyvinyl chloride is the nigh pop material especially for gravity sewers (49% in Almere and 36% in Breda). In Almere, the youngest city in the Netherlands largely built after 1970, the existence of two dissimilar sub-systems is profound: a storm sewer system constructed mainly of concrete pipes and a dry waste matter water sewer system constructed mainly of PVC. In Breda, there is a variation of installed plastic pipes in terms of structure materials and types of application (storm water, wastewater and combined system).

The test of the available inspection data sets reveals the presence of a range of defects, affecting the structural stability, flow regime and leak tightness of the system. Figure 4 presents the occurrence rate of such defects in PVC pipes (number of defects normalised per kilometre), classified according to NEN 3399 (2015). In this study, the defects are grouped without because the level of severity in club to recoup for the uncertainty involved in CCTV inspections (Dirksen et al., 2013).

A review on the durability of PVC sewer pipes: enquiry vs. practice

Published online:

08 October 2019

Figure iv. The number of defects per kilometre observed in CCTV inspections for PVC sewer pipes in two Dutch municipalities: Almere (bluish) and Breda (red).

Figure 4. The number of defects per kilometre observed in CCTV inspections for PVC sewer pipes in ii Dutch municipalities: Almere (blue) and Breda (ruby-red).

Detailed exploration of the bachelor information sets proved that there is not a clear pattern that could link the use of a PVC piping, a specific range of diameters or other characteristics of the organization to increased levels or sectional types of defects. This fact might exist attributed to the express bachelor data (506 km of PVC pipes in Almere and 206 km in Breda), particularly since there is a minimal variation in the data set up of Almere.

Another approach was implemented for the PVC pipes (2.iv km) in the municipality of Amstelveen. In an effort to verify whether the degradation of PVC systems is depicted, inspection data of pipes that have been inspected twice was explored. This analysis (Figure 5) reveals an increment in the occurrence rate of the initially institute defects, followed by the advent of new ones (breaks, fissures and root intrusion). These changes are noticed inside a timespan of 7–8 years.

A review on the immovability of PVC sewer pipes: research vs. practice

Published online:

08 October 2019

Figure 5. The number of defects per kilometre observed in CCTV inspections of the aforementioned PVC sewer pipes in the municipality of Amstelveen in 2003 (blue) and in 2010/2011 (red).

Figure 5. The number of defects per kilometre observed in CCTV inspections of the same PVC sewer pipes in the municipality of Amstelveen in 2003 (blue) and in 2010/2011 (red).

Disquisitional aspects

Evaluation of the literature

Inspection data indicates that PVC is the most used structure textile for sewer systems. Although some researchers focused on operating PVC pipes in sewers, research was restricted to measuring only deflection levels (Moser et al., 1990; Walton & Elzink, 1989) or conducting visual-based assessments (Meerman, 2008). Bauer (1990) fabricated a more comprehensive assessment of an operating pipe, but testing included merely one pipe which had served for 15 years only. Additionally, despite some visual assessments of the joints used in sewer pipes (Bauer, 1990; Meerman, 2008), there is hardly any relevant research reported on the effect of the sewer surroundings on the elastomeric textile backdrop and performance. At that place are indications, however, that the hostile environs that prevails in sewer systems (acids, FOG, etc.) has an impact on certain sealing materials, such as natural rubber and styrene–butadiene prophylactic (Plastics Manufacture Pipe Clan [PIPA], 2009). Moreover, add-on of certain mixture components and softeners in the production of sealing rings could trigger a blazon of material incompatibility with PVC pipes, resulting eventually in corrosion and leakages (Stein, 2001).

The need for comprehensive testing is implied by this literature review. For instance, while a connection between extrusion quality and tensile backdrop could exist partially established in one study (Alferink et al., 1995), this was unfeasible in another case (Whittle & Tennakoon, 2005). In fact, in the latter study a concrete holding (i.e. specific gravity) was utilised to explain the differences in the mechanical (tensile) backdrop.

Comparing and combining results from different researchers in club to draw conclusions is challenging, due to a.o. a lack of uniformity in materials and methods applied. The conditions and methods of specimen preparation and testing are based on different standardised (ISO, ASTM, Equally/NZ) or non-standardised methods. Additionally, the production quality of new pipes used every bit reference specimens has changed over the years, making the direct comparing with aged pipes only indicative. Finally, comparing private properties with respect to the requirements of norms for prophylactic functioning of PVC sewer pipes does non provide any indication apropos fabric deposition, as the exact initial atmospheric condition are still unknown.

A property that is used extensively in design and classification of gravity sewer pipes is pipe stiffness. Research (Välimaa, 1982) has proved that under high soil covers (as for sewer pipes), pipe stiffness is not the most crucial parameter. All the same, it is expected to become significant for house connections which are usually placed nether soil covers <0.8 m. Besides that, in the explored literature a defoliation between ring (or nominal) stiffness and pipe stiffness has been noticed. The corresponding formulas as included in ISO 9969 (2016) (Equation (9)) and ASTM D 2412 (Equation (x)) are provided for description: (9) $$S=\left(0.0186+0.025·\frac{y}{d}\right)\frac{F}{L·y}$$ (ix) where $S(\mathit{\text{or SN}})$ is the ring stiffness, $y$ is the deflection (1000), $d$ is the average inside diameter, $F$ is the applied force (kN) and $L$ is the length of the exam piece (thousand). (ten) $$PS=\frac{F}{{\Delta }_y}$$ (x) where $PS$ is the pipe stiffness, $F$ is the applied force (N/m) and ${\Delta }_y$ is the deflection (m).

In terms of elastic modulus, ring and pipage stiffness are expressed equally (Moser & Folkman, 2008): (11) $$SN=\frac{\mathrm{Due\; east}·I}{D^{\mathrm{iii}}}$$ (11) (12) $$P\mathrm{South}=\frac{\mathrm{six.7}·E·I}{r^3}=53.7·\frac{E·I}{D^{\mathrm{iii}}}$$ (12) where $\mathrm{Due\; east}$ is the modulus of elasticity (Pa), $I$ is the moment of inertia of pipage wall per unit length (m⁴/yard) and $D$ is the mean diameter (thou). An additional remark apropos pipe stiffness is on its attributed unit of measurement. Using kPa or psi for this belongings has no physical pregnant and defoliation among engineers may exist caused. As indicated in Equations (9) and (10), pipage stiffness is a measure out of the resistance of a pipe expressed as a ratio between the applied linear loading in the longitudinal direction (kN/one thousand) and the vertical deflection in the radial direction (m). Therefore, the unit should exist strictly notated as kN/1000_linear/m_deflection or lbf/in_linear/in_deflection instead of kPa (=kN/yard²=loading/area) or psi (lbf/in.^two) respectively.

Inconsistency between scientific literature and practice

A recent written report (Kuliczkowska & Zwierzchowska, 2016) presented a range of early defects found on newly installed PVC sewer pipes during CCTV inspections. These defects included dents due to installation or soil compaction, excessive deflections, buckling and improper longitudinal slopes. Inspection information from Breda and Almere indicates that boosted defects may emerge: surface damage, fissure, displaced/destroyed sealing ring, root intrusion and interruption/collapse. Given the limitations that exist in CCTV inspections due to subjectivity of the inspector and but inner pipe inspection (Dirksen et al., 2013; Van Riel, 2017), defects not reported may too occur as CCTV inspections likely result in an optimistic gauge of the pipe'south status.

Although linking the observed defects in CCTV to the actual physical country of a pipage is arduous (Van Riel, 2017), it is quite apparent that there is a certain gap between scientific enquiry and what is observed in practice. Relevant studies (Folkman, 2014; Meerman, 2008; Whittle & Tennakoon, 2005) suggest that PVC sewer pipes are expected to exceed a 100 years of lifetime, whereas inspection data suggests that astringent defects (cracks and fissures) already exist.

The virtually emphasised discrepancy is observed regarding the performance of elastomeric joints. The literature (Arsénio, 2013; Meijering et al., 2004) indicates that leakage is possible just under extreme cases (deflection, >36%; bending angle, >10° and complete pull-out) and root intrusion is impossible, given that installation is proper (Sadler et al., 2001). Even so, this comes in contrast to the presented failure rates (Figures four and 5), as well as the results of CCTV inspections published concerning Sweden (Östberg, Martinsson, Stål, & Fransson, 2012; Ridgers, Rolf, & Stål, 2006; Stål, 1998) and Kingdom of denmark (Randrup, 2000). Practical installation techniques (proper laying and jointing) could be considered as an indisputable contributing cistron (Stein, 2001; Stephens & Gill, 1982); however, information technology is unknown whether or not information technology is the only or almost significant one.

Conclusions

Production, installation and functioning include numerous factors which can affect the lifetime of a PVC pipe. These factors appear to interact with each other under sure weather resulting in different failure mechanisms. Four lifetime prediction models (i.due east. SEM, Arrhenius equation, LEFM and quality number) have been utilised in the literature in social club to describe some of these failure mechanisms and conclude on the rest lifetime of plastic pipes. However, given their limitations, the predicted lifetimes are certainly open up to dispute, every bit no model encompassing all possible failure mechanisms has been proposed even so.

Research on material degradation reveals that the backdrop of PVC sewer pipes in operation have not altered significantly or at all, whereas a lifetime that exceeds 100 years is ordinarily suggested. Only 1 case of failure is recorded, apropos a sewer main, and the failure was attributed to poor extrusion quality. However, there is no published inquiry on the upshot of sewage on the elastomeric seals of PVC systems.

Inspection data from three Dutch municipalities highlights that PVC sewer pipes accept already developed all types of known defects, whereas deposition evolves with time at a relatively fast rate. Assay of a larger inspection data set will allow the detection of a possible connection between defects (types, rates) and elements of the system (diameter, type of drainage piping, soil cover, etc.).

There is a certain discrepancy between literature and observations in practice on the issue of lifetime expectancy of PVC sewer pipes. This emphasises the demand for farther material properties assessment of operating PVC sewer pipes and elastomeric joints. Additionally, just comprehensive testing of physical, mechanical and chemical backdrop could yield rubber conclusions regarding the level of degradation and its origins. In the literature, efforts to determine merely private properties accept proved to be inadequate, leading to inconsistencies and unanswered questions.

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Source: https://www.tandfonline.com/doi/full/10.1080/15732479.2019.1673442

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