- Email: [email protected]
Swagelining as a method of pipelines rehabilitation
Journal of Materials Processing Technology 157–158 (2004) 637–642
Swagelining as a method of pipelines rehabilitation G. Wr´obel∗ , M. Szymiczek, Ł. Wierzbicki Department of Processing of Metals and Polymers, Faculty of Mechanical Engineering, Silesian University of Technology, Konarskiego St. 18a, 44-100 Gliwice, Poland
Abstract The present study outlines the advantages of using trenchless methods for the rehabilitation of pipelines made of steel, concrete, cast iron etc. The trenchless technologies have been widely applied for the rehabilitation of various pipelines such as sewage systems, gas pipelines or water supply systems. There has been characterized the swagelining technology which is based on one of the metal working technologies and namely the sinking of pipes. The PE pipe stress in the drawing die zone has been analysed and an attempt has been made to analyse the mechanisms causing the elastic recovery of PE pipes. There have also been presented the diameter changes as the parameter of the elastic recovery which is a result of our own research conducted in accordance with the program developed. © 2004 Published by Elsevier B.V. Keywords: Swagelining; Pipelines; Rehabilitation
1. Introduction The recent 10 years have seen a substantial increase in the length of water supply systems, gas pipelines and sewage water systems (see Table 1). At the same time the pipelines made of traditional materials suffer breakdowns as a result of long years in service thus causing a threat to the natural environment. Factors which influence most the ageing processes and the increased failure frequency are the intensified vehicular traffic, changes in properties of transported media, stray currents, changes in the underground water level and the soil contamination [1]. The deteriorating condition of water supply and sewage systems enforce the development of new rehabilitation techniques, with main focus on the trenchless methods. The trenchless technologies constitute efficient replacement to the traditional pipelines rehabilitation methods due to the substantial reduction or elimination of trenching, protection of the natural environment and considerable reduction of costs including social costs. A further proof of the increased interest in the subject techniques is the Poland’s access to the International Society for Trenchless Technology (ISTT) ∗
Corresponding author. E-mail address: [email protected] (G. Wr´obel).
0924-0136/$ – see front matter © 2004 Published by Elsevier B.V. doi:10.1016/j.jmatprotec.2004.07.150
which took place at the 17th International “No-Dig” Fair ’99 [2]. In order not to allow a situation where it is no longer possible to rehabilitate the pipeline using a trenchless technology detailed surveys and site investigations of the pipelines must be carried out. First an examination of the soil and water conditions must be performed as well as the depth at which the pipeline to be rehabilitated is laid must be determined. Further an inspection of the pipeline condition should be made with special attention being paid to the material, shape and length of individual sections. To this end a number of analyses of both the soil and the pipeline condition are made. The analysis of the pipeline condition is usually made by means of the CCTV inspection or using a sonar or a radar (used as addition to the data acquired using the CCTV) prior to which a thorough cleaning of the duct must be performed [3]. Apart from the above mentioned systems of the acquisition of data important for the pipeline rehabilitation there are also systems enabling an inspection of ducts which are partially filled. They are TV cameras used above the water surface and sonar transponders employed below the water surface. In order to chart location maps of the area of works including all obstacles located in the ground (light pipes, cables, pipes, etc.) georadars are used [4]. A precise examination of the overall condition of the pipeline and the cause of the failure enables the optimum
638
G. Wr´obel et al. / Journal of Materials Processing Technology 157–158 (2004) 637–642
Table 1 Water supply system, sewage system and gas grid development in Poland [1] Municipal infrastructure
Infrastructure as for 31st December 1970
1980
1990
1998
Water supply system Main pipeline (km) Distributor pipeline (km) Service connections (piece)
3406.1 26075.6 637200
6092.9 53128.4 1203200
8266.9 93187.3 1969700
29236.7 194711.3 3560590
Sewage system Combined sewage system (km) Charge connections (piece)
13898.6 342500
20496.9 568800
26514.7 568800
42961.5 946665
Gas grid Distributor pipeline (km) Service connections (piece)
11843 302700
22402.3 490000
45826.7 1004400
91288.9 1741029
selection of the repair technology and a substantial reduction of costs. There are many trenchless pipeline rehabilitation technologies available in the market. They differ in e.g. the material the pipe is made of, the shape of the pipe or the method of inserting it to the pipeline to be rehabilitated. At this juncture, we should mention the most frequently used ones which are the “compact pipe”—an insert C-pipe, insituform—the insert is a “stocking” made of acid resistant polyester fibre soaked with resins, relining—short sections of PE-, PVC-, and PP-pipes are connected using couplings or spigot-andsocket joints. It is swagelining that seems to be the most inexpensive and the simplest alternative for the above technologies that employs the plastic working technology of the drawing of pipes. The technology allows a tight fitting of the PE pipes inside the rehabilitated pipeline. This applies both to the operation stage forming in the drawing die zone and the elastic recovery after the insertion into the rehabilitated pipeline. This study focuses on the swagelining technology which was developed by British Gas North Western Region at the end of the 1970s and introduced in the commercial scale in the 1980s. First attempts to rehabilitate pipelines by means of that technology were made with the use of pre-heated insert “getting-through” pipes. The result of the heating process was the reduction of the drawing damages. However, the process required the additional equipment to be employed, which was the reason for many problems during the reconstruction. The development of the technology and its constant improvement resulted in pulling the PE pipes into the reconstructed host pipe without additional preheating of the insert pipe. The technology of drawing PE pipes without preheating was used for the first time in Chester in 1989 [5]. 2. Technolgy charactersitics The subject technology is based on the plastic working technology of sinking of pipes. The traditional sinking is the type of plastic working of metal or polymer materials. It is used for permanent shap-
ing of the material, changing the physical and mechanical properties, modification of structure or generation of internal stresses. These are achieved through the plastic strain. Generally, it must be noted that the plastic working operations are accompanied by some negative effects including, but not limited to: • springing—occurs in case of the forming of plastics due to the low value of Young’s modulus (approximately 1/100 of the value for metals), • elastic recovery—caused by viscoelastic properties of plastics. The latter effect proves advantageous when using the sinking for the renovation of pipelines as it allows a tight fitting of the polyethylene lining inside the rehabilitated pipeline. Hence, such a use of the sinking constitutes the “viscoelastic working”. Cold plastic forming of plastics is usually performed in temperatures higher than the glass transition temperature. However, since the glass transition temperature of some plastics (PC) is relatively high, their cold working is carried out in the glassy state. One of the most important advantages of the plastic working processes is the improvement of mechanical properties of the materials formed [7]. However, a difference must be noted between the behaviour of thin- and thick-walled pipes when pulled through the die where, in case of the former the wall thickening is observed, while the wall gets thinner in case of the latter. The sinking process itself generates significant stresses whose value depends on the diameter reduction ratio [6]. In order not to allow the destruction (caused by high stresses) of the liner inserted into the rehabilitated host pipe, the liner remains under permanent load which enables the stresses to be partially compensated. The best adherence of the PE pipe (PE pipes are used of the nominal diameter higher by 2–5% than the inner diameter of the rehabilitated pipe) is achieved when pulling the pipe through the die with the approach angle of 10–15% at the speed of 3–5 m/min. The result of the operation is the diameter reduction of approximately 12% which enables to
G. Wr´obel et al. / Journal of Materials Processing Technology 157–158 (2004) 637–642
639
Fig. 1. Reconstruction efficiency for the SDR series of PE pipes [5].
insert the PE pipe, without any additional resistance, into the rehabilitated host pipe. Once the repair is completed the PE pipe expands and its construction becomes strengthened under the conditions of tight fitting in the rehabilitated pipeline which is of particular importance if a possibility exists to exceed the self-support limit under conditions of ground factors influence. A number of advantages can be noticed resulting from the pulling process being performed in “cold” conditions. The advantages include: reduction of the number of additional equipment, possibility of quicker stopping the process which enables to weld the joint with additional service lines and to resume and complete the installation. Another significant problem is the reconstruction efficiency measured by the flow rate in the new pipe to the flow ratio in the old conduit ratio, the pressure drop value being maintained. The research carried out by ERS British Gas [5] showed that the increase in the flow rate can be achieved through the wall thickness reduction which is illustrated in Fig. 1. The inner fin resulting from the butt welding of the pipe is also of some importance. The fin constitutes resistance to the flow thus the reconstruction efficiency is reduced.
Fig. 2. Forces and stresses in the drawing (sinking) process [3].
ameter increase or swelling are observed and therefore the pipe remains under load. Once the tension is released the PE pipe returns to the original size. Such a natural return is the result of the viscoelastic recovery. During the process the elastic recovery is more rapid after the leaving of the die zone and on releasing the tension. In the remaining time, when lacking the tension – after the complete release of the pipe – or under the conditions of the tension being fixed, the recovery is slower. Eventually this is to ensure a tight fitting of the inserted PE pipe in the pipeline being rehabilitated. The process analysis may not, however, disregard the plastic strains causing permanent reduction of the inserted pipe diameter. Such strains are the result of the partial plasticizing of the material in the die zone. The actual stresses inside the wall of the pipe being pulled in depend on the drawing speed. The speed influences the time the pipe remains inside the die and the speed of strains as well as the extent of the plastic strains. Consequently, a conclusion can be drawn that it takes the properly adjusted drawing speed enabling an insertion of the pipe into the rehabilitated pipeline with simultaneous elastic recovery to achieve an efficient drawing process.
3. Stress analysis The drawing process causes the material to deform due to following external forces: efforts (active forces) (F: drawing load) and reactions (Fr : tool reaction, Ft : friction force) (Fig. 2). The above forces cause the internal stresses to occur in the material drawn. The axial–symmetric stresses are characteristic for the sinking of pipes where the following stresses are observed [6]: • axial stresses (tensile stresses) σ 1 , • radial stresses (compressive stresses) σ r , • circumferential stresses (compressive stresses) σ . The value of the drawing load F depends on the properties, dimensions, size and elastic recovery of the material drawn as well as on the tool geometry. There is also a significant, indirect dependence on the process temperature. The process analysis shows that the material in the die zone is partially plasticized. On leaving the die, a rapid di-
4. Own research An attempt was made under this study to create a basis for the rational selection of the conditions of the pipe drawing as the trenchless method of the rehabilitation of pipelines. The assessment was made basing on the data published and the research performed, taking into account geometric parameters of the die, drawing force and speed, properties of the material the pipe was made of as well as the pipe dimensions. The research was carried out in the laboratory of the Department of Processing of Metals and Polymer Materials. A Heckert FPZ 100/1 testing machine (Fig. 3) was adapted for the purpose of testing. A tensile test was performed with the die mounted in the traverse cassette. The machine speed – being at the same time the speed of the die – was 529.47 mm/min. In order to determine the dependence of the elastic recovery on the geometric pa-
640
G. Wr´obel et al. / Journal of Materials Processing Technology 157–158 (2004) 637–642
Fig. 3. Test stand and die. Table 2 Geometric parameters of die Angle 12.5◦ Reduction ratio
15◦ (%)
17.5◦
10 15 20
rameters of the die, different die generator inclination angles were used and the reduction ratio was diversified (see Table 2).
Under the research, in order to determine the subject elastic recovery, the following PE pipes were used: PE100Ø63 SDR 11 and SDR 17 manufactured by ELPLAST PLUS in Jastrz˛ebie Zdr´oj. The tests were carried out in the ambient temperature of 21 ± 2 ◦ C. During the testing the outer diameters were measured in specific intervals and the tensile force was recorded. The results of the tests performed enabled the determination of the dependence of the drawing force on the geometric parameters of the die and the series of the pipes tested (see Fig. 4).
Fig. 4. Drawing force and the reduction ratio.
G. Wr´obel et al. / Journal of Materials Processing Technology 157–158 (2004) 637–642
641
Fig. 5. Diameter change as a function of time.
There are two areas visible in the figure, first of them for SDR 11 – values from 6.8 to 10.9 kN and the other one – for SDR 17 with significantly lower force values ranging from 4.3 to 7.4 kN which is the result of the wall thickness. In order to determine the elastic recovery of the pipe the outer diameter was measured. The diameter was measured in fixed intervals counted from the drawing process completion. Due to the ovality of the pipes drawn the arithmetic mean of five measurements was assumed. The process analysis demonstrates that the material in the die zone is plasticized. On leaving the die, a rapid diameter increase or swelling are observed caused by the release of the alternating load. Further stage is the process of the viscoplastic recovery under conditions of the axial load and after the release thereof. In the tests performed the tension was released after 1 min time which is reflected in the presented diagram of the diameter change as a function time (see Fig. 5). The diagram illustrates the successive stages of the elastic recovery—pulling through the die (die), “swelling” (up to 1 min after leaving the die), tension release (after 1 min), further return to the original diameter (from 1 to 3000 min).
5. Conclusions The lower the series number of the pipe pulled in and thus the thicker the pipe wall, the higher the drawing force. This results from the resistance the pipe drawn must overcome in the die zone. The elastic recovery varies according to the die angle and the reduction ratio. The elastic recovery increases as the die angle and the reduction ratio increase. The thicker the wall the more intense is the recovery. The most intense elastic recovery of the pipe tested takes place during the initial 30 min after the completion of the drawing test. Quantitative characteristics of the process will be used in the procedures of selecting tools and materials for individual reconstructions. References [1] A. Roszkowski, Renowacje ruroci˛ag´ow – teoria i praktyka, Materiały konferencyjne III Konferencji Naukowo-Technicznej, Nowe technologie w sieciach i instalacjach wodno-kanalizacyjnych. [2] Technologie bezwykopowe: Jeste´smy w ISTT, Warszawa, 1999. [3] Polska Fundacja Technik Bezwykopowych: Vademecum bezwykopowych technologii, renowacji, napraw i wymiany ruroci˛ag´ow i instalacji podziemnych, Technologie bezwykopowe, Warszawa, 2003.
642
G. Wr´obel et al. / Journal of Materials Processing Technology 157–158 (2004) 637–642
[4] A. Cinaciara, Zastosowanie Georadar´ow do Inwentaryzacji Infrastruktury Podziemnej. In˙zynieria Bezwykopowa, Dompress, Warszawa, 2003. [5] L.B. Behenna, K. Hicks, Swagelining—the ERS. Died, Buried and Forgotten, Gas Engineering and Management, 1993.
´ ask, [6] E. Grochowski, F. Grosman, Maszyny Ci˛agarskie Wydawnictwo Sl˛ 1976. [7] K. Bielefeldt, Wpływ walcowania i gł˛ebokiego tłoczenia na niekt´ore własno´sci mechaniczne krajowego poliw˛eglanu i politrioksanu, Praca doktorska, Zileona G´ora, Wrocław, 1976.
Swagelining as a method of pipelines rehabilitation G. Wr´obel∗ , M. Szymiczek, Ł. Wierzbicki Department of Processing of Metals and Polymers, Faculty of Mechanical Engineering, Silesian University of Technology, Konarskiego St. 18a, 44-100 Gliwice, Poland
Abstract The present study outlines the advantages of using trenchless methods for the rehabilitation of pipelines made of steel, concrete, cast iron etc. The trenchless technologies have been widely applied for the rehabilitation of various pipelines such as sewage systems, gas pipelines or water supply systems. There has been characterized the swagelining technology which is based on one of the metal working technologies and namely the sinking of pipes. The PE pipe stress in the drawing die zone has been analysed and an attempt has been made to analyse the mechanisms causing the elastic recovery of PE pipes. There have also been presented the diameter changes as the parameter of the elastic recovery which is a result of our own research conducted in accordance with the program developed. © 2004 Published by Elsevier B.V. Keywords: Swagelining; Pipelines; Rehabilitation
1. Introduction The recent 10 years have seen a substantial increase in the length of water supply systems, gas pipelines and sewage water systems (see Table 1). At the same time the pipelines made of traditional materials suffer breakdowns as a result of long years in service thus causing a threat to the natural environment. Factors which influence most the ageing processes and the increased failure frequency are the intensified vehicular traffic, changes in properties of transported media, stray currents, changes in the underground water level and the soil contamination [1]. The deteriorating condition of water supply and sewage systems enforce the development of new rehabilitation techniques, with main focus on the trenchless methods. The trenchless technologies constitute efficient replacement to the traditional pipelines rehabilitation methods due to the substantial reduction or elimination of trenching, protection of the natural environment and considerable reduction of costs including social costs. A further proof of the increased interest in the subject techniques is the Poland’s access to the International Society for Trenchless Technology (ISTT) ∗
Corresponding author. E-mail address: [email protected] (G. Wr´obel).
0924-0136/$ – see front matter © 2004 Published by Elsevier B.V. doi:10.1016/j.jmatprotec.2004.07.150
which took place at the 17th International “No-Dig” Fair ’99 [2]. In order not to allow a situation where it is no longer possible to rehabilitate the pipeline using a trenchless technology detailed surveys and site investigations of the pipelines must be carried out. First an examination of the soil and water conditions must be performed as well as the depth at which the pipeline to be rehabilitated is laid must be determined. Further an inspection of the pipeline condition should be made with special attention being paid to the material, shape and length of individual sections. To this end a number of analyses of both the soil and the pipeline condition are made. The analysis of the pipeline condition is usually made by means of the CCTV inspection or using a sonar or a radar (used as addition to the data acquired using the CCTV) prior to which a thorough cleaning of the duct must be performed [3]. Apart from the above mentioned systems of the acquisition of data important for the pipeline rehabilitation there are also systems enabling an inspection of ducts which are partially filled. They are TV cameras used above the water surface and sonar transponders employed below the water surface. In order to chart location maps of the area of works including all obstacles located in the ground (light pipes, cables, pipes, etc.) georadars are used [4]. A precise examination of the overall condition of the pipeline and the cause of the failure enables the optimum
638
G. Wr´obel et al. / Journal of Materials Processing Technology 157–158 (2004) 637–642
Table 1 Water supply system, sewage system and gas grid development in Poland [1] Municipal infrastructure
Infrastructure as for 31st December 1970
1980
1990
1998
Water supply system Main pipeline (km) Distributor pipeline (km) Service connections (piece)
3406.1 26075.6 637200
6092.9 53128.4 1203200
8266.9 93187.3 1969700
29236.7 194711.3 3560590
Sewage system Combined sewage system (km) Charge connections (piece)
13898.6 342500
20496.9 568800
26514.7 568800
42961.5 946665
Gas grid Distributor pipeline (km) Service connections (piece)
11843 302700
22402.3 490000
45826.7 1004400
91288.9 1741029
selection of the repair technology and a substantial reduction of costs. There are many trenchless pipeline rehabilitation technologies available in the market. They differ in e.g. the material the pipe is made of, the shape of the pipe or the method of inserting it to the pipeline to be rehabilitated. At this juncture, we should mention the most frequently used ones which are the “compact pipe”—an insert C-pipe, insituform—the insert is a “stocking” made of acid resistant polyester fibre soaked with resins, relining—short sections of PE-, PVC-, and PP-pipes are connected using couplings or spigot-andsocket joints. It is swagelining that seems to be the most inexpensive and the simplest alternative for the above technologies that employs the plastic working technology of the drawing of pipes. The technology allows a tight fitting of the PE pipes inside the rehabilitated pipeline. This applies both to the operation stage forming in the drawing die zone and the elastic recovery after the insertion into the rehabilitated pipeline. This study focuses on the swagelining technology which was developed by British Gas North Western Region at the end of the 1970s and introduced in the commercial scale in the 1980s. First attempts to rehabilitate pipelines by means of that technology were made with the use of pre-heated insert “getting-through” pipes. The result of the heating process was the reduction of the drawing damages. However, the process required the additional equipment to be employed, which was the reason for many problems during the reconstruction. The development of the technology and its constant improvement resulted in pulling the PE pipes into the reconstructed host pipe without additional preheating of the insert pipe. The technology of drawing PE pipes without preheating was used for the first time in Chester in 1989 [5]. 2. Technolgy charactersitics The subject technology is based on the plastic working technology of sinking of pipes. The traditional sinking is the type of plastic working of metal or polymer materials. It is used for permanent shap-
ing of the material, changing the physical and mechanical properties, modification of structure or generation of internal stresses. These are achieved through the plastic strain. Generally, it must be noted that the plastic working operations are accompanied by some negative effects including, but not limited to: • springing—occurs in case of the forming of plastics due to the low value of Young’s modulus (approximately 1/100 of the value for metals), • elastic recovery—caused by viscoelastic properties of plastics. The latter effect proves advantageous when using the sinking for the renovation of pipelines as it allows a tight fitting of the polyethylene lining inside the rehabilitated pipeline. Hence, such a use of the sinking constitutes the “viscoelastic working”. Cold plastic forming of plastics is usually performed in temperatures higher than the glass transition temperature. However, since the glass transition temperature of some plastics (PC) is relatively high, their cold working is carried out in the glassy state. One of the most important advantages of the plastic working processes is the improvement of mechanical properties of the materials formed [7]. However, a difference must be noted between the behaviour of thin- and thick-walled pipes when pulled through the die where, in case of the former the wall thickening is observed, while the wall gets thinner in case of the latter. The sinking process itself generates significant stresses whose value depends on the diameter reduction ratio [6]. In order not to allow the destruction (caused by high stresses) of the liner inserted into the rehabilitated host pipe, the liner remains under permanent load which enables the stresses to be partially compensated. The best adherence of the PE pipe (PE pipes are used of the nominal diameter higher by 2–5% than the inner diameter of the rehabilitated pipe) is achieved when pulling the pipe through the die with the approach angle of 10–15% at the speed of 3–5 m/min. The result of the operation is the diameter reduction of approximately 12% which enables to
G. Wr´obel et al. / Journal of Materials Processing Technology 157–158 (2004) 637–642
639
Fig. 1. Reconstruction efficiency for the SDR series of PE pipes [5].
insert the PE pipe, without any additional resistance, into the rehabilitated host pipe. Once the repair is completed the PE pipe expands and its construction becomes strengthened under the conditions of tight fitting in the rehabilitated pipeline which is of particular importance if a possibility exists to exceed the self-support limit under conditions of ground factors influence. A number of advantages can be noticed resulting from the pulling process being performed in “cold” conditions. The advantages include: reduction of the number of additional equipment, possibility of quicker stopping the process which enables to weld the joint with additional service lines and to resume and complete the installation. Another significant problem is the reconstruction efficiency measured by the flow rate in the new pipe to the flow ratio in the old conduit ratio, the pressure drop value being maintained. The research carried out by ERS British Gas [5] showed that the increase in the flow rate can be achieved through the wall thickness reduction which is illustrated in Fig. 1. The inner fin resulting from the butt welding of the pipe is also of some importance. The fin constitutes resistance to the flow thus the reconstruction efficiency is reduced.
Fig. 2. Forces and stresses in the drawing (sinking) process [3].
ameter increase or swelling are observed and therefore the pipe remains under load. Once the tension is released the PE pipe returns to the original size. Such a natural return is the result of the viscoelastic recovery. During the process the elastic recovery is more rapid after the leaving of the die zone and on releasing the tension. In the remaining time, when lacking the tension – after the complete release of the pipe – or under the conditions of the tension being fixed, the recovery is slower. Eventually this is to ensure a tight fitting of the inserted PE pipe in the pipeline being rehabilitated. The process analysis may not, however, disregard the plastic strains causing permanent reduction of the inserted pipe diameter. Such strains are the result of the partial plasticizing of the material in the die zone. The actual stresses inside the wall of the pipe being pulled in depend on the drawing speed. The speed influences the time the pipe remains inside the die and the speed of strains as well as the extent of the plastic strains. Consequently, a conclusion can be drawn that it takes the properly adjusted drawing speed enabling an insertion of the pipe into the rehabilitated pipeline with simultaneous elastic recovery to achieve an efficient drawing process.
3. Stress analysis The drawing process causes the material to deform due to following external forces: efforts (active forces) (F: drawing load) and reactions (Fr : tool reaction, Ft : friction force) (Fig. 2). The above forces cause the internal stresses to occur in the material drawn. The axial–symmetric stresses are characteristic for the sinking of pipes where the following stresses are observed [6]: • axial stresses (tensile stresses) σ 1 , • radial stresses (compressive stresses) σ r , • circumferential stresses (compressive stresses) σ . The value of the drawing load F depends on the properties, dimensions, size and elastic recovery of the material drawn as well as on the tool geometry. There is also a significant, indirect dependence on the process temperature. The process analysis shows that the material in the die zone is partially plasticized. On leaving the die, a rapid di-
4. Own research An attempt was made under this study to create a basis for the rational selection of the conditions of the pipe drawing as the trenchless method of the rehabilitation of pipelines. The assessment was made basing on the data published and the research performed, taking into account geometric parameters of the die, drawing force and speed, properties of the material the pipe was made of as well as the pipe dimensions. The research was carried out in the laboratory of the Department of Processing of Metals and Polymer Materials. A Heckert FPZ 100/1 testing machine (Fig. 3) was adapted for the purpose of testing. A tensile test was performed with the die mounted in the traverse cassette. The machine speed – being at the same time the speed of the die – was 529.47 mm/min. In order to determine the dependence of the elastic recovery on the geometric pa-
640
G. Wr´obel et al. / Journal of Materials Processing Technology 157–158 (2004) 637–642
Fig. 3. Test stand and die. Table 2 Geometric parameters of die Angle 12.5◦ Reduction ratio
15◦ (%)
17.5◦
10 15 20
rameters of the die, different die generator inclination angles were used and the reduction ratio was diversified (see Table 2).
Under the research, in order to determine the subject elastic recovery, the following PE pipes were used: PE100Ø63 SDR 11 and SDR 17 manufactured by ELPLAST PLUS in Jastrz˛ebie Zdr´oj. The tests were carried out in the ambient temperature of 21 ± 2 ◦ C. During the testing the outer diameters were measured in specific intervals and the tensile force was recorded. The results of the tests performed enabled the determination of the dependence of the drawing force on the geometric parameters of the die and the series of the pipes tested (see Fig. 4).
Fig. 4. Drawing force and the reduction ratio.
G. Wr´obel et al. / Journal of Materials Processing Technology 157–158 (2004) 637–642
641
Fig. 5. Diameter change as a function of time.
There are two areas visible in the figure, first of them for SDR 11 – values from 6.8 to 10.9 kN and the other one – for SDR 17 with significantly lower force values ranging from 4.3 to 7.4 kN which is the result of the wall thickness. In order to determine the elastic recovery of the pipe the outer diameter was measured. The diameter was measured in fixed intervals counted from the drawing process completion. Due to the ovality of the pipes drawn the arithmetic mean of five measurements was assumed. The process analysis demonstrates that the material in the die zone is plasticized. On leaving the die, a rapid diameter increase or swelling are observed caused by the release of the alternating load. Further stage is the process of the viscoplastic recovery under conditions of the axial load and after the release thereof. In the tests performed the tension was released after 1 min time which is reflected in the presented diagram of the diameter change as a function time (see Fig. 5). The diagram illustrates the successive stages of the elastic recovery—pulling through the die (die), “swelling” (up to 1 min after leaving the die), tension release (after 1 min), further return to the original diameter (from 1 to 3000 min).
5. Conclusions The lower the series number of the pipe pulled in and thus the thicker the pipe wall, the higher the drawing force. This results from the resistance the pipe drawn must overcome in the die zone. The elastic recovery varies according to the die angle and the reduction ratio. The elastic recovery increases as the die angle and the reduction ratio increase. The thicker the wall the more intense is the recovery. The most intense elastic recovery of the pipe tested takes place during the initial 30 min after the completion of the drawing test. Quantitative characteristics of the process will be used in the procedures of selecting tools and materials for individual reconstructions. References [1] A. Roszkowski, Renowacje ruroci˛ag´ow – teoria i praktyka, Materiały konferencyjne III Konferencji Naukowo-Technicznej, Nowe technologie w sieciach i instalacjach wodno-kanalizacyjnych. [2] Technologie bezwykopowe: Jeste´smy w ISTT, Warszawa, 1999. [3] Polska Fundacja Technik Bezwykopowych: Vademecum bezwykopowych technologii, renowacji, napraw i wymiany ruroci˛ag´ow i instalacji podziemnych, Technologie bezwykopowe, Warszawa, 2003.
642
G. Wr´obel et al. / Journal of Materials Processing Technology 157–158 (2004) 637–642
[4] A. Cinaciara, Zastosowanie Georadar´ow do Inwentaryzacji Infrastruktury Podziemnej. In˙zynieria Bezwykopowa, Dompress, Warszawa, 2003. [5] L.B. Behenna, K. Hicks, Swagelining—the ERS. Died, Buried and Forgotten, Gas Engineering and Management, 1993.
´ ask, [6] E. Grochowski, F. Grosman, Maszyny Ci˛agarskie Wydawnictwo Sl˛ 1976. [7] K. Bielefeldt, Wpływ walcowania i gł˛ebokiego tłoczenia na niekt´ore własno´sci mechaniczne krajowego poliw˛eglanu i politrioksanu, Praca doktorska, Zileona G´ora, Wrocław, 1976.