Report for Handbook on large plastic pipes, published 2015, ISBN

Size: px

Start display at page:

Download "Report for Handbook on large plastic pipes, published 2015, ISBN"

Amanda Price
6 years ago
Views:

Relining with large diameter Polyethylene Pipes Damaged and leaky pipes made out o concrete, GRP, steel, ductile iron can be relined and renovated with Proiled Polyethylene Pipes in almost every

However, the use o proiled pipes, especially in big diameters, creates new stable pipe systems with a high static load capacity.

1 Relining with large diameter Polyethylene Pipes Damaged and leaky pipes made out o concrete, GRP, steel, ductile iron can be relined and renovated with Proiled Polyethylene Pipes in almost every diameter. Here, the old pipe serves as an empty conduit or the new pipe made out o PE and thereore a completely new, sel-contained pipe system can be built. However, the use o proiled pipes, especially in big diameters, creates new stable pipe systems with a high static load capacity. or the static calculation o the new pipeline two things must be taken into consideration, the installation process and the operating condition o the pipeline. The new system will beneit rom the extremely long service lie o polyethylene pipes (> 100 years). old and damaged sewer new relined sewer The relining process with polyethylene pipes has proven its reliability in almost all ields o application or many years: Renovation o leaky sewer pipelines Renovation o corroded drinking water pipelines Provide a seal against leakage or iniltration Gas supply systems (Changeover to higher operational pressures) Renovation o inverted siphons Industrial applications (aggressive media, acids, alkalis etc.) During the relining process with large-diameter polyethylene pipes, the pipe lengths are either inserted or drawn-in according to the application and environmental conditions. Which procedure will be selected depends essentially on the space conditions prevailing on site and o course on the existing machines and tools. The occurring load or polyethylene pipes is completely dierent during the pulling through process in comparison to the insertion. This must be considered when dimensioning, during the selection o materials and in the selection o the pipe connection.

Pulling through process During the pulling through o a pipeline, the pipeline is exposed to axial tensile loading. This leads to an expansion o the pipe.

2 Pulling through process During the pulling through o a pipeline, the pipeline is exposed to axial tensile loading. This leads to an expansion o the pipe. This eect is reinorced by the bending loads which can arise in the angles o the old pipeline. The insertion orces are increasingly dependent on the length o the pipe to be installed, the weight o the pipeline, the ring gap, the interior surace o the old pipe or rather the riction between the old and the new pipe. The old pipe must be cleaned and i possible encrustations removed. It is also advisable to apply enough lubricant in order to reduce the riction. Water is also oten used or this reason. Separate sliders which are ixed on the outside o the new PE pipe or in the old pipe. The choice o the correct product or the reduction o the rictional resistance always depends on the corrosion status and the cleaning condition. The choice o the pipe jointing method can also have an inluence on the arising riction orces; this is particularly the case i a socket is reducing the ring gap. The external pipe surace is mechanically stressed during the pulling through process. Notches and grooves can occur and must be considered when making the static analysis. Notches and grooves can be a weak spot regarding the durability o a new pipe system. The PE raw materials were continuously optimized in recent years, especially or this kind o load. Advanced polyethylene pipe materials o strength grade MRS 8 or MRS 10 have thereore a greater groove insensitiveness and resistance to slow crack growth. The pipe producers are indicating special values o many kinds in their data sheets according to several testing methods (Notch-Test, 2-NCT, NCT, ESCR etc.). These should give inormation, or at least a reerence point, regarding the resistance against slow crack growth. Depending on the respective country and the application there are oten nationally deined minimum values. Typical requirements or creep rupture are: NCT > 300 h Notch Test > 500 h Specially optimized PE100 pipe materials, called PE 100 RC (RC Resistant to crack) reach even higher values. The maximum permissible load during the pulling through process depends on the selected pipe wall cross-section and on the selected welding method. The load transmission o the pull rope or o the pull rod into the pipe must occur very evenly in order to reduce additional loads. It is recommendable to use a tension-head or tension anchors which need to be distributed at the periphery. A measuring device must be integrated within the pulling system in order to monitor the orce application. The measuring device is able to advise the personnel when the tensile load exceeds the permitted degree due to unoreseen obstacles or a too high riction resistance. The pulling through process must be closely monitored and comprehensively documented. Especially angular delections within the pipe string can lead to an unexpectedly high tensile resistance.

or the calculation o the permissible tensile orce, the expected loading duration and the ambientpipe temperatures have to be taken into account.

3 or the calculation o the permissible tensile orce, the expected loading duration and the ambientpipe temperatures have to be taken into account. The tensile loading can last a ew minutes or several hours depending on the length o the pulled pipe segments. In practice, the load period is oten set with 24 hours. The corresponding tensile dimensioning can be taken rom the creep strength curves, which are listed in the relevant standards or which are provided by the respective pipe producers. Aax σ CW ax S ax axial orces [N] A ax axial area [mm²] σ design strength [N/mm²] or the required time and temperature C W Welding actor [-] S saety actor [-] The respectively thinnest and weakest wall thickness is the decisive actor or the dimensioning, especially in the ield, o proiled pipes. Thereore all pipe elements (pipes, ittings, joints) have to be considered. The welding actor can be ound in the applicable standards. or large diameter Electrousion-Joints the manuacturer s instructions has to be considered. The quality o the welding joint technology can be analyzed by testing according to DVS2203. Welding actor or butt-usion and extrusion welding acc. DVS /2205-1: Welding Process PEHD PP Heated Tool Butt Welding z 0,9 0,9 s 0,8 0,8 Hot Gas Extrusion Welding z 0,8 0,8 s 0,6 0,6 When using electro-usion sockets, it should be noted that the transerable shearing stress comes to around 50 % o the acceptable hoop stress. or the calculation o the subject to shear welding area, the interruption by welding wire must be considered.

4 Shear orce loaded area Interupted welding area by welding wire ax Aw σ CW 2 S ax axial orces [N] A w welding area (without wire area) [mm²] σ design strength [N/mm²] or the required time and temperature C W Welding actor [-] S saety actor [-] Push in procedure During insertion o the pipe line, the line is not loaded on tension, it is primary loaded on distortion, buckling and compression. The loading duration is similar to the pulling through process and depends on the length o the pipe strings. or the calculation o the compression stress it is possible to apply to the creep strength curves. The typical values o the pressure resistance are normally higher, however, it is useul to keep the deormation exposed through higher stresses relatively small in order to prevent orming o the shape o the pipe. The ormulas used or the distortion and buckling are relecting the ideal circular /cylindrical condition. The stronger the pipe deviates rom this, the lower is the resistance against distortion and buckling (Stability Consideration). ormula or calculation o critical length: L k 2 E Pi I ax S pipe L k ax buckling length [mm] axial compression orces [N] I pipe Moment o Inertia o pipe! [mm 4 ] E lexural modulus [N/mm²] (or the required time and temperature) S saety actor [-] (or stability calculations 2)

5 with: I pipe ( ID + 2 eequ ) Pi 64 ( ID) I pipe Moment o Inertia o pipe! [mm 4 ] ID Inner diameter pipe [mm] e equ equivalent wall thickness pipe [mm] (at solid wall pipes wall thickness) 4 4 Euler case 4 is equal to the situation o Relining-Pipe: Euler Case 1 Euler Case 2 Euler Case 3 Euler Case 4 L L K 2 L L K L L K 0,707 L L K 0,5 L

6 Injection grout mortar When designing the new pipe or taking the load by soil, traic etc. the space between the old and new pipe must be illed with injection grout mortar. This procedure is necessary to generate a deined load situation. Static calculations or relining pipes can be done according to ATV M127. During the injection procedure the pipe is stressed by radial buckling. The buckling pressure depends on the injection pressure and hydrostatic pressure due to the density o the grout mortar and the height between the pipe and grout mortar tank. The radial buckling resistance o a pipe can be calculated as ollows: p 3 20 E eequ k 3 2 ( 1 µ ) ( ID + eequ ) S E lexural modulus [N/mm²] or the required time and temperature ID inner diameter pipe [mm] e equ equivalent wall thickness pipe [mm] (at solid wall pipes wall thickness) S saety actor [-] (should be 2 or stability calculations) urthermore the liting orce during the injection process must be kept in mind. A distance holder at the crown between the old and the new pipe can reduce the liting orce. In any case, the liting orce must be lower than the weight orce o the considered pipe segment between two distance holders. To avoid loating o the new pipe, the pipe can also be illed with water during injection o the grout mortar. liting Pi OD 4 2 L g ( ρ gm ρ ) w Liting Liting orce [N] OD Outer diameter pipe [m] L Pipe length [m] g Gravity (9,81 m/s²) ρ gm Density grout mortar [kg/m 3 ] ρ w Density o medium inside pipe [kg/m 3 ]

7 In summary, there are many load cases to consider or designing a relining-pipe-system. The described technical backround show only a part o it and o course there is more. But at the end all based on physical eects and plastic engineering! Plaspitec provide Engineering and Consultancy or plastic pipes Systems! Author: Stephan üllgrabe Plaspitec GmbH, Germany

THERMOPLASTIC MANHOLES FOR AND OUT OF LARGE DIAMETER PIPES

THERMOPLASTIC MANHOLES FOR AND OUT OF LARGE DIAMETER PIPES Introduction: Manholes are, beside pipes and fittings, an essential element of underground pipe-systems. They are used for maintenance and the