THE DEVELOPMENT OF TWO-LAYER LINING METHOD FOR PREVENTING BREAKAGE OF GREY CAST IRON PIPES

Transcription

1 THE DEVELOPMENT OF TWO-LAYER LINING METHOD FOR PREVENTING BREAKAGE OF GREY CAST IRON PIPES Seita Shimizu, Pipeline Technology Center Tokyo Gas Co., Ltd. Takashi Shigefuji, Pipeline Technology Center Tokyo Gas Co., Ltd. Hiroki Kikuchi, Pipeline Technology Center Tokyo Gas Co., Ltd. Masato Nakayama, Pipeline Technology Center Tokyo Gas Co., Ltd. 1. INTRODUCTION Tokyo Gas is a vertically integrated natural gas supply business encompassing every stage from production to sales centered on Tokyo and its surroundings: the largest metropolitan center in Japan. In this region, Tokyo Gas operates a total of more than 40,000 kilometers of pipelines that form its principal transport and supply system. Tokyo Gas operates about 80% of this pipeline system at a low operating pressure of less than 3kpa, because although the importance of transporting and supplying gas at medium and high pressures has increased in Japan as a result of progress in deregulation such as that seen in the electric power retail industry in recent years, essentially most of the demand for gas in Japan has been for water heating and kitchen use in homes and businesses. When the social and legal responsibility of gas enterprises for guaranteeing public safety in Japan is considered in the light of such circumstances, it can be stated that maintenance work carried out to maintain the safety of its low pressure pipelines is an extremely important task of Tokyo Gas. A high percentage of those pipelines with diameter exceeding 100 mm are buried in areas of high population density and heavy traffic load, and if any trouble such as leakage of these pipelines occurs, it has serious impact on society and on public safety. Therefore, Tokyo Gas has, based on certain stipulated priorities, implemented preventive maintenance measures to prevent leakage of its grey cast iron pipelines that have deteriorated and are assumed to be at the highest potential risk of leakage. To support this program, it has worked aggressively to develop countermeasure methods rehabilitation and renovation measures. For example,we have developed the Pipe-in-Pipe method, the Cured-in-Place method and others, and achieved considerable success in executing measures for grey cast iron pipe, and have established an adequate menu of countermeasure methods. But to respond to the recent intensified competition between different categories of energy and other rapid changes in the business environment, we face a growing need to further reduce our countermeasure costs and accelerate countermeasures, and must develop methods that can be applied cheaply and more frequently as quickly as possible. The response that we have prepared to meet this challenge is the Two-layer lining method that we introduce in this report. This method, a brand new approach completely different from existing countermeasure methods for grey cast iron pipes, is executed by, instead of using molded material such as a pipe or seal hose liner, using two kinds of instant-cured resin to form a lining membrane with tensile strength and elongation equal to or superior to molded material on the inside surface of the existing pipe at the execution site. Furthermore, because it is unnecessary to cut off and reconnect lateral connection pipes and it is suitable for widely used piping systems, it is a method that offers superior cost benefits. The detailed principles and specifications for its equipment and materials etc. are introduced in detail in this report. 2. TECHNICAL SUBJECT OF PRESENT TECHNOLOGY Table 1 summarizes the scope of applicability of the existing methods to our piping system. The content of the table has been limited to specifications of methods that are used by Tokyo Gas(FlexLiner and PALTEM), and it reveals that the Pipe bursting method is remarkably influenced by bends and other aspects of piping form. There are also upper limits on the number of bends and number of connecting pipes that can be handled by other methods imposed by resistance to insertion and restrictions on

2 execution time. Because the numbers of both bends and lateral connection pipes are increasing in cities, there has been a strong trend at actual work sites to establish spans shorter than the spans shown in the table, and in many cases, the adoption of the trenchless technical method one in which the fixed costs account for a high percentage of work costs regardless of the length cannot fully obtain the benefits of its use. Pipe-in-Pipe Method Pipe Bursting Method Cured-in-Place Method Figure 1. Image of Present Technology for Renovating Grey Cast Iron Pipes Table1. Scope of Application of Present Technology Diameter 1 span length 45-degree Bends Lateral reconnection Flex Liner (Pipe in Pipe) More than 100mm Less than 100m OK ( max4/span ) Need ( max 5/span ) Pipe Bursting More than 100mm Less than 50m NG Need ( max 5/span ) PALTEM (Cured in Place) More than 100mm Less than 200m OK Need ( max 5/span ) We have responded to this challenge by developing the Two-layer lining method. The specifications and performance of this method are described in detail below. 3. THE DEVELOPMENT OF TWO-LAYER LINING METHOD The goals that guided the development of the Two-layer lining method were maximizing the benefits obtainable from the trenchless technical method by resolving the major shortcomings of existing technologies namely the increase in the number of excavation locations or the reduction of span length resulting from quantitative restrictions imposed by bends and lateral connection pipes on our pipeline system and forming membranes with high long-term durability in order to reduce life-cycle costs. The primary goals of the development of the equipment specifications were compact size and low manpower requirements to achieve superior workability and lower costs. The lining material specifications were set not only to guarantee its adequate mechanical strength, but also its applicability to a wide range of industrial applications so that its cost can be reduced easily by mass production. The following paragraphs summarize the conceptual design and the judgement standards applied to determine detailed specifications of this method to satisfy the required specifications, the specifications of the materials and the machinery and equipment that were selected, and introduce an outline of the Two-layer lining method.

3 3.1. Arrangement of Resin As its name indicates, the Two-layer lining method is a method of preventing gas from leaking from a damaged grey cast iron pipe by applying two layers of two kinds of resin. This detailed description of the method begins with an explanation of the effects of applying a two layer lining. Normal corrosion prevention resin lining methods line the interior surface of a pipe by transporting epoxy resin with a pig or an air current. When trial applications of this method have been carried out to form a single layer lining inside a grey cast iron pipe, its behavior when the pipe is damaged is revealing that it cannot be counted on to prevent gas leaks. This phenomenon is not a result of the modulus or ductility of the resin; the results are identical even when material such as polyurethane resin with several hundred percent elongation is used. This is caused by the fact that a resin layer bonded to the inside surface of a pipe with force of 2 to 4 MPa is stretched from zero span by displacement of a damaged pipe. To resolve this problem, we proposed forming the lining membrane with two kinds of resin with differing modulus. It is an application of the concept of applying multi-layer waterproof sheets on mortar panels to make waterproof flooring material. When a pipe lined with a two layer resin membrane is damaged, the resin with low modulus follows and absorbs the displacement so that its effect is not transmitted to the high modulus resin layer (See Fig.2). In the case of Single- layer Grey cast iron pipe Single resin membrane Event of crack Event of displacement In the case of Double- layer Grey cast iron pipe Event of crack Low modulus resin High modulus resin Event of displacement disjunctum maintain initial form without displacement Figure 2. Behavior of two-layer lining membrane in the event of crack and displacement As a result, even if the lining is subjected to displacement exceeding the breakage limit, its durability is not reduced after the damage because shear separation of the low modulus layer protects the high modulus layer from the effects of the displacement so that it retains its original thickness. This concludes the explanation of the reasons for developing the Two-layer lining method and its effects. The next step is the establishment of the lining materials that can maximize these effects Choice of lining materials When selecting the resin, we knew that this method must be alternatives for the Pipe-in- Pipe method. The resin used to form the high modulus layer that will play the role of the pipe body after

4 damage to the original pipe must, therefore, have tensile strength and elongation equal or superior to that of medium density polyethylene that is used for our low pressure pipes. And because a Two-layer lining is formed by multiple linings, it must harden quickly and it must be easy to apply in coats. Therefore, we eliminated epoxy resin that is used for the normal corrosion prevention resin lining method from the list of candidates, and based on the results of a survey of high performance resins that can be formed by a lining process (see Table 2), we focused on a resin called polyurea that is widely used to prevent cracking of concrete structures. Table2. Typical properties of plastic materials Tensile Stress at break Elongation at break Cure time MD PE 20Mpa > 600% - Polyurea 32Mpa 300% 3 second Polyurethane 12Mpa 400% 5 second Epoxy ( lining use) 20Mpa 54% > 5 hour Polyurea is a instant cured two-fluid compound resin that is made by pressure mixing source fluids preheated to about 70 C near an outlet. Its physical properties are tensile stress at break of 30MPa and elongation at break of 300%, both superior to polyethylene. Thanks to its extraordinary high performance physical properties, the use of polyurea as lining for concrete structures and for other uses is increasing extremely rapidly, and it is the perfect material for grey cast iron pipes that require similar crack protection measures. And as the low modulus resin that will be sacrificed when damage occurs, we selected polyurethane resin that has elongation higher than that of polyurea. Based on the results of this consideration, the materials we selected were polyurethane directly on the pipe s inner surface and polyurea as the second layer. And the resin configuration was established at a first layer of 1.0 mm of polyurethane and a second layer of 2.0 mm of polyurea (see Fig. 3). Grey cast iron pipe Polyurethane : 1.0mm Polyurea : 2.0mm Tensile strength elongation Polyurethane 12Mpa 400% Polyurea 32Mpa 300% Figure 3. Arrangement of resin for two-layer lining method 3.3. Technology Choice of Lining Method The following is an explanation of the specific membrane formation technologies combined to form the resin configuration explained above. The two most popular methods of forming a membrane for the

5 normal resin lining method are using a rubber ball called a pig to form a lump of fluid resin inserted into the pipe and applying the resin on the inside surface by transporting it with a current of air. But neither of the above methods could be adopted, because the resins used for this method are instant cured resins that cure within a few seconds after the two fluids are mixed. So the spray device used by the compressed mixing method shown in Fig. 5 is inserted into the pipes and as it is moved constantly through the pipes, it lines the inside surface. And branches are not blocked by excessive resin and the specifications in the rough design are assured because the spray device is controlled so that only the necessary quantity per unit surface area is sprayed. After the establishment of the basic specifications for the so-called core of the method the configuration of the lining membranes and their formation method the next step in the development was the design of the work procedure and the design of the materials and equipment in preparation for its completion. Prior to the concrete explanation of the development, the process and application specifications, including those discussed above, that are necessary for the method to satisfy the basic specifications and target cost while guaranteeing the required performance are summarized below. It must be possible to execute it in a span of 70 m without blocking lateral connection pipes. It must be capable of preventing gas leaks from joints or a damaged pipe. Before lining, dust and mill scale must be removed from the inside of the pipe and surface treatment performed, and the lining must assure enough adhesive strength to withstand later cutting of the pipe and the installation of new branch pipes. It must provide adequate long-term durability to prevent constituents in the gas and soil from causing excessive decline of its performance. Equipment that must be developed to realize the method based on these points are shown in Table 3. Table 3. Development item to be required Work Process Item Role CLEANING Scraper wire brush Swabber descale rust polishing surface discharging dust SURFACE FINISHING primer and primer spray gun enhancing adhesion force LINING resin dispensing system spray gun and spray nozzle supplying resin to spray gun lining pipe and sealing joint direction direction scraper wire brush swabber primer supply hose primer spray gun primer Figure 4. Outline of cleaning and surface finishing items

6 Dispensing system Puller for a gun lateral Another pipe Spray nozzle Spray gun Resin membrane Figure 5. The outline of lining devices and Lining cut sample 3.4. Process of operation The Two-layer lining method work process can be broadly categorized as pit construction and pipe cutting, purging gas from the pipe and cleaning its inside surface, lining the pipe, pipe reconnection, and backfilling. The actual work and time required to complete an execution include, in addition to the processes mentioned above, setting up barriers around the work area, setting machinery, and preparing the resin. And the normal execution time is about 8 hours for every 50 m. This complies with the standard authorized underground installation work time in Japan. The required manpower depends on the construction of the launch pit and reception pit. Based on past work performed by other methods, it is estimated that it can be done by between 8 and 10 workers including the foreman Evaluation of lining membrane As explained in the previous paragraphs, by combining various technologies to develop this method, we have succeeded in forming a membrane with high strength and elongation on a pipe wall that cannot be matched by any existing resin lining method. The performance of a membrane formed by a lining process is not evaluated based only on its mechanical values; it is important to evaluate its ability to reliably prevent leaking caused by the breakage of a grey cast iron pipe and how well it assures that the membrane will remain in sound condition over a long period when later work is executed on a pipes lined by this method. These properties are normally evaluated by bending testing, cyclic bending testing, creep testing, chemical resistance testing, and pipe body hole cutting testing. Table 4 and Table 5 summarize the results of bending testing, pipe body hole-cutting testing, and chemical resistance testing of the polyurea: three tests that have already been performed among those which should be performed. Although the polyurethane has been evaluated because it is assumed that it will exfoliate when damage occurs, a detailed discussion of the results are omitted here. A detailed explanation of the evaluation standards is also omitted because of a shortage of space, but the rehabilitation and repair work evaluation standards of the Japan Gas Association were applied and the chemicals that were the object of the chemical resistance testing are typical chemicals found in natural gas and in the soil environment established by these standards.

7 Table 4. Evaluation Result Bending test Hole-sawing test (Tapping test) Evaluation standards There s no gas leakage, when pipe was broken by bending load. There s no exfoliation of membrane, when a hole was made on pipe by hole-sawing cutter. Result OK OK Figure 6. Result of bend test and hole-sawing test Table 5. Evaluation Result of chemical resistance test ( maceration span 120days ) Degradation rate Tensile strength Elongation Weight tertiary butyl mercaptan (1v/v%) -2.6% +11.5% +0.8% distilled water -14.4% +2.7% +2.7% sodium hydroxide solution (ph 1) -12.0% +0.2% +1.8% sulfuric acid solution (ph 13) -7.3% +4.3% +2.9% natrium chloride solution (5w/w%) -3.7% +5.0% +1.6% Initial value Tensile strength : 28Mpa Elongation: 280% limit of degradation rate Tensile strength:-20% Elongation:-20% Weight: -3% or +14% The evaluation results show that the Two-layer lining method satisfies the acceptance standards set for all items, and confirms its capacity to prevent leaks caused by the behavior of pipes that have been damaged, and to maintain its sound condition during later work. A comparison of an evaluation of its long-

8 term durability in its operating environment with that of existing lining materials has shown that it deteriorates extremely little and is sufficiently adaptable. And a quantitative evaluation of its methane permeability performed in addition to the main evaluation shows that its coefficient of permeability is 4.82E-16(mol*m/m 2 *sec*pa). A comprehensive judgement of the above results,though additional testing (creep test etc.) is required, shows that a resin membrane formed on the inside of a pipe by the Two-layer lining method can maintain high mechanical strength for a long period, and that the application of this method permits the continued reliable operation of a grey cast iron pipe without replacement Scope of application Because the Two-layer lining method can be applied to pipes with almost any shape including bends and can be executed by excavating only the launch pit and reception pit, it eliminates the increase in the number of excavations caused by the number of lateral connection pipes, prevents the shortening of the spans, and it is far simpler to execute than other methods in urban centers with a high concentration of consumers premises. The scope of application of the method is shown in Table 6. Table 6. The scope of application Type of pipe Pressure Diameter Size of pit Grey cast iron pipe Less than 0.1 Mpa More than 100mm Launch pit: W1.0m L2.5m H1.5m Reception pit: W1.0m L3.0m H1.5m span of application Applicable figure of piping system Up to 70m Within four 45-degree bends 4. ADVANTAGE OF TWO-LAYER LINING METHOD The advantages of applying the Two-layer lining method are broadly categorized as its cost benefits and its good working properties. These two benefits are discussed below Cost As stated above, the Two-layer lining method can be executed in a single span up to a maximum length of 70 m with only two excavations: the launch pit and the reception pit. It also completely eliminates the shortening of span length and the increase in the number of excavations caused by bends and by lateral connection pipes that are restrictions for other methods. And because its materials and machinery are simple, they can be rented at very low rates. Figure 7 compares its execution cost with the costs of the existing methods when replacement is considered to be 100%. This represents the case of the execution of each method on a 50 m length of pipe buried at a depth of 1.2 m, and shows that the Twolayer lining method is superior in terms of its cost to other grey cast iron pipe countermeasure methods.

9 Replacement 100 Pipe-in-Pipe method 60 Pipe-Bursting method 50 Two-Layer Figure 7. Cost comparison among renovating methods for grey cast iron pipes 4.2. Working property A consideration of the superior work properties of the Two-layer lining method shows that in addition to the good work properties it provides thanks to the small amount of soil that is excavated, it has three more benefits. Even though it is a resin lining method, the workers do not have to touch the resin because many steps in its execution are mechanized and automated. Differing from existing methods, a pipe that has been lined by this method can be easily maintained because it can be cut or connected new branch pipes just like a normal pipe. Because the lining materials are instant cured materials, it is unnecessary to use hot water or steam to encourage its hardening or restoration as it is when using the Cured-in-Place method and the pipe in pipe method. Regarding the first of these three benefits, now that regulations concerning safety from chemicals have been strengthened by, for example, the announcement of the MSDS, it is not an exaggeration to state that preserving workers health is even more important than cost considerations. 5. CONCLUSION This report has presented an outline of the Two-layer lining method and an explanation of its characteristics, and ends with the following conclusions concerning the applicability of the method. We have successfully developed a grey cast iron pipe countermeasure method that can be applied to piping systems very flexibly without the need for excavations at customers connecting point branches ( lateral connection pipes ). The Two-layer lining method is far less costly and its working properties are superior compared with those of existing methods at the same time as it can form high strength and high durability membranes and guarantee performance good enough to be alternative for existing methods. For Tokyo Gas that serves many districts with high concentrations of customers, this method that can be applied in any execution environment will make a huge contribution to accelerate countermeasures for the security of gas infrastructure. The seismic performance of the Two-layer lining method will be evaluated in future, and although the earthquake risk must be quantified, considering the probability of an earthquake occurring, the use of the

10 method should be promoted to take advantage of its cost superiority and to constantly accelerate the improvement of security of gas infrastructure,even if it has no seismic resistance. 6. ACKNOWLEDGEMENT I wish to express my deep appreciation to the staff of Hakko Co., Ltd. that participated in this development project and to the technical staff of Tokyo Gas for their appropriate and useful advice.