| 1. |
|
|
| 2. |
- Bergström, Gunnar, et al.
(författare)
-
Acceptanskriterier för repor och intryck i plaströr Accpetance criteria for scratches and indentations in plastic pipes
- 2009
-
Rapport (refereegranskat)abstract
- Development of materials and laying techniques have arisen the question how scratches and indentations in plastics pipes affect the strength and technical lifetime of pipelines. Scratches may occur both in the manufacturing of the pipes, in connection with the installation and subsequent maintenance. The problems in assessing the failure risk from scratches and indentations are similar for pipes used in gas and water distribution and in district heating applications. Therefore, a broad effort to identify the risks in relation to current pipe materials is technically and economically justified. The project has aimed to evaluate the effect of scratches and indentations on the technical lifetime of plastics pipes and to present criteria for maximum allowable depth of scratches and indentations. The study on pressure pipes focused on the conditions for scratched polyethylene pipes to achieve a lifetime of 50 years. It is noted that a scratch damage can not be judged solely on the basis of its depth and sharpness. To assess the impact of the scratch on the serviceability of the pipe, consideration must also be taken to the material from which the pipe was made and the safety factor used in the design. Extensive pressure tests show that pipes made of modern materials can withstand surface scratches to a higher degree than pipes of older materials. For pipes made of modern bimodal PE80 and PE100 materials, scratches up to 10% depth may be accepted without reduction of rated pressure. However, for pipes of older material, a reduction in pressure may be required already at smaller scratches. The study also indicates that for the same relative scratch depth, a greater reduction in pressure is required with increasing pipe dimension. The study on the non pressure pipes shows that the studied polypropylene pipes resist both deep scratches combined with ovalization and large indentations without any cracks penetrating the pipe wall. However, the extent and development of crazing and surface cracking vary with scratch depth, deformation level and material. The test pipes were subjected to extreme conditions very rarely or never occurring in practice. This suggests that small scratches at moderate ovalization and realistic indentations in temperatures around room temperature do not affect the lifetime of the pipes. One objective of the project was to develop a method for the evaluation of the scratch resistance of a pipe. In the proposed test method the force needed to produce a specified scratch is measured. This force is used as a relative measure of the scratch resistance of a pipe material when compared to other materials. In order to assess to what extent a scratch affects the lifetime of the pipe, the depth of the scratch must be estimated with reasonable accuracy. Since the scratch in many cases is found on existing pipelines the method must be suited for field use. To achieve that a simple instrument for scratch depth measurements was made and evaluated.
|
|
| 3. |
- Bergström, Gunnar, et al.
(författare)
-
Accpetance criteria for scratches and indentations in plastic pipes
- 2009
-
Rapport (refereegranskat)abstract
- Development of materials and laying techniques have arisen the question how scratches and indentations in plastics pipes affect the strength and technical lifetime of pipelines. Scratches may occur both in the manufacturing of the pipes, in connection with the installation and subsequent maintenance. The problems in assessing the failure risk from scratches and indentations are similar for pipes used in gas and water distribution and in district heating applications. Therefore, a broad effort to identify the risks in relation to current pipe materials is technically and economically justified. The project has aimed to evaluate the effect of scratches and indentations on the technical lifetime of plastics pipes and to present criteria for maximum allowable depth of scratches and indentations. The study on pressure pipes focused on the conditions for scratched polyethylene pipes to achieve a lifetime of 50 years. It is noted that a scratch damage can not be judged solely on the basis of its depth and sharpness. To assess the impact of the scratch on the serviceability of the pipe, consideration must also be taken to the material from which the pipe was made and the safety factor used in the design. Extensive pressure tests show that pipes made of modern materials can withstand surface scratches to a higher degree than pipes of older materials. For pipes made of modern bimodal PE80 and PE100 materials, scratches up to 10% depth may be accepted without reduction of rated pressure. However, for pipes of older material, a reduction in pressure may be required already at smaller scratches. The study also indicates that for the same relative scratch depth, a greater reduction in pressure is required with increasing pipe dimension. The study on the non pressure pipes shows that the studied polypropylene pipes resist both deep scratches combined with ovalization and large indentations without any cracks penetrating the pipe wall. However, the extent and development of crazing and surface cracking vary with scratch depth, deformation level and material. The test pipes were subjected to extreme conditions very rarely or never occurring in practice. This suggests that small scratches at moderate ovalization and realistic indentations in temperatures around room temperature do not affect the lifetime of the pipes. One objective of the project was to develop a method for the evaluation of the scratch resistance of a pipe. In the proposed test method the force needed to produce a specified scratch is measured. This force is used as a relative measure of the scratch resistance of a pipe material when compared to other materials. In order to assess to what extent a scratch affects the lifetime of the pipe, the depth of the scratch must be estimated with reasonable accuracy. Since the scratch in many cases is found on existing pipelines the method must be suited for field use. To achieve that a simple instrument for scratch depth measurements was made and evaluated.
|
|
| 4. |
- Bergström, Gunnar, et al.
(författare)
-
Durability testing for 100 year lifetime for buried non-pressure plastic pipes
- 2006
-
Ingår i: Plastics Pipes XIII.
-
Konferensbidrag (refereegranskat)abstract
- For plastics pipes used for underground drainage and sewerage there is at present no internationally accepted method for the evaluation of durability. This makes it difficult to make an objective assessment for both new materials and new pipe designs entering the market. This paper presents a possible future structure of such a durability evaluation for nonpressure pipes. Based on an experimental study of pipes made from a filled and an unfilled PP material and one made from an HDPE material different damage mechanisms and changes in pipe characteristics were observed when the pipes were exposed to long-term deflection and long term (one-year) ageing at +95 °C. A CAED methodology is also described which was used to investigate the distribution and time dependence of pipe stresses.
|
|
| 5. |
- Forsaeus Nilsson, Stefan, 1972, et al.
(författare)
-
Brittle fracture in casing pipes
- 2006
-
Ingår i: 10th International Symposium on District Heating and Cooling.
-
Konferensbidrag (refereegranskat)
|
|
| 6. |
- Forsaeus Nilsson, Stefan, 1972, et al.
(författare)
-
Damage to coated plastics pipes from trenchless laying techniques
- 2006
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This project aims at evaluating an external coating on plastics pipes; and its protective function against scratches and scoring damage from trenchless laying techniques. PE100 pressure pipes with four different coatings were tested in horizontal drilling and pipe bursting field trials. During the tests, the lengthwise and cross-sectional deformations of the pipe were measured along with the traction force. The pipes’ surfaces were examined with respect to scratches, and the depth of the most prominent ones were determined. Of the two laying techniques, pipe bursting was the one that caused the deepest scratches. Horizontal drilling was not significantly worse than ordinary handling during transport and preparation with respect to scratch depth. Dragging of the pipe above ground on asphalt surfaces caused severe damage to the pipe wall. The deepest scratches were seen on two pipe selections with soft coatings. Due to their thickness, however, these coatings were not penetrated and thus successfully protected the main pipe wall. The hardest coating tested, made of polypropylene, was also the thinnest one, and it was penetrated at one location during the pipe bursting test. The traction force on the pipe was significantly higher during horizontal drilling than during pipe bursting. On the other hand, ovalisation of the pipe’s cross-section was greater during pipe bursting.
|
|
| 7. |
- Forsaeus Nilsson, Stefan, 1972, et al.
(författare)
-
Skador på skyddsmantlade plaströr vid grävningsfri förläggning
- 2005
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This project aims at evaluating an external coating on plastics pipes, and its protective function against scratches and scoring damage from trenchless laying techniques. PE100 pressure pipes with four different coatings were tested in horizontal drilling and pipe bursting field-trials. During the tests, the lengthwise and cross-sectional deformations of the pipe were measured along with the traction force. The pipes’ surfaces were examined with respect to scratches, and the depth of the most prominent ones were determined. Of the two laying techniques, pipe bursting was the one causing the deepest scratches. Horizontal drilling was not significantly worse than ordinary handling during transport and preparation with respect to scratch depth. Dragging of the pipe above ground on asphalt surfaces caused severe damage to the pipe wall. The deepest scratches were seen on two pipe alternatives with soft coatings. Due to thic kness, however, these coatings were not penetrated and thus successfully protected the main pipe wall. The hardest coating tested, a polypropylene alternative, were also the thinnest one, and was penetrated at one location during the pipe bursting test. The traction force on the pipe was significantly higher during horizontal drilling than during pipe bursting. On the other hand, ovalisation of the pipe’s cross-section was greater during pipe bursting.
|
|
| 8. |
- Forsaeus Nilsson, Stefan, 1972, et al.
(författare)
-
Spröda brott i mantelrör
- 2005
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Vid ett flertal tillfällen har Rapid Crack Propagation (RCP) inträffat i mantelröret hos stora fjärrvärmerör. RCP är ett mycket snabbt sprickförlopp där sprickan drivs fram av ringdragspänningar i mantelröret. Det är ett problem framför allt vid arbete på rören i låga temperaturer. Dels blir mantelrörsmaterialet sprödare då det kyls ned, och dels gör en temperatursänkning att ringdragspänningar byggs in i mantelröret då det förhindras att dra ihop sig av stålrör och PUR-skum. RCP-sprickor i fjärrvärmemantelrör har dokumenterats vid temperaturer kring –18 °C men sannolikt har fenomenet inträffat i enstaka fall redan vid några grader under noll. Tre olika polyetenmaterial utvärderades med avseende på risken för spröda brott i mantelrör. Dels ett unimodalt material av PE80-kvalitet som har använts i stor utsträckning tidigare, dels ett modernare unimodalt PE80-material som används emellanåt idag och slutligen ett bimodalt PE80-material av en kvalitet som för närvarande används av de flesta tillverkare. Generellt sett är modernare material avsevärt tåligare med avseende på spröda brott då det är en viktig utvecklingsparameter hos råmaterialtillverkarna. Provningar genomfördes på polyetenrör av både stor (upp till 630 mm diameter) och liten (160 mm) dimension. Ett hanteringsprov genomfördes där rören kyldes ned och bearbetades med elverktyg på samma sätt som sker i fält. Här uppstod ett RCP-brott vid –25 °C under skärarbete med vinkelslip på ett rör med diameter 500 mm av det modernare unimodala PE80 materialet. Samma material sprack även vid slagprovning enligt SS-EN 253 vid –20 °C på såväl liten som stor dimension. Den bimodala polyetenvarianten klarade båda provningarna utan brott. En serie slagprov genomfördes på rör med diameter 160 mm med en egenutvecklad provningsmetodik med avsikten att ringa in kritiska temperaturer och temperaturspänningsnivåer vid vilka man bör iaktta särskild försiktighet. Resultaten visar att det bimodala polyetenmaterial som provats är så tåligt med avseende på spröda brott att det knappast är förknippat med någon större risk att hantera dem i normalt vinterklimat. Det äldre materialet, som sprack vid hanteringsprov och slagprov enligt SS-EN 253, är dock betydligt känsligare och en spänningsanalys visar att det, för stora dimensioner, finns en påtaglig risk för sprödbrott redan vid temperaturer några grader under noll. Slagsegheten hos de olika materialen har också utvärderats med sk Charpyslagprovning, som provningsmässigt är betydligt enklare att genomföra än slagprov i fullskala på hela rör. Även här var syftet att bestämma en kritisk omslagstemperatur mellan segt och sprött beteende. Tydliga skillnader kunde ses mellan de olika polyetenkvaliteterna. Sannolikt finns en korrelation mellan resultaten från Charpyprov och rörslagprov. Emellertid saknas statistiskt underlag för att dra några kvantitativa slutsatser, men med mer underlag skulle metoden troligtvis kunna användas för klassificering och kravgränser.
|
|
| 9. |
|
|
| 10. |
- Sällström, Jan Henrik, et al.
(författare)
-
Minskning av risken för skador på gasledningar genom djupförläggning och användandet av grävskydd (Reducing the risks for gas pipe damages through deep digging and the use of protective plates)
- 2013
-
Rapport (refereegranskat)abstract
- This report concerns part 2 of a project with the aim to propose protective measures for cables and pipelines for bio and natural gas. Part 1 was previously reported in SGC Rapport 2011:239. The wish is to be able to increase the pressure in the distribution networks from 4 to 10 bar without having to retain the safety distances valid for 80 bar pipelines. Polymer, concrete and steel protective plates, and deep digging are the physical measures considered. In part 1 a survey was made, in part by an enquiry, of the frequency, causes and consequences of incidents where pipelines were hit by excavators. Further, the rules and standards were investigated in countries where 7–10 bar pipelines are already in service. Here, in part 2 the perspective was widened to include, apart from gas pipelines, also all kinds of buried pipelines and cables. Now a visit to a supplier in France is reported, as well as an vestigation of costs and environmental impacts of the different protective measures, and an analysis of the strength of protective plates and of how they can best be positioned in the ground in relationship to the pipeline. The main result from the study visit to France was that new regulations mean that both new and existing pipelines have to be satisfactorily protected. For the physical point of view these plastic protective plates play an important part, and there are commercially available building systems of plates for which the strength and durability have been verified by tests. In the full scale experiments done in, e.g., France, it can be concluded that the plastic (HDPE) plates can wit stand high loads which are applied by use of a bucket with teeth mounted on an excavator. In some cases penetration of teeth occurs, but the plates will in that case either come up and alert the operator or stay in the ground and still protect the buried cable or pipeline. Concrete plate can also break, but the pieces are held together by the steel reinforcement. The analysis of costs and environmental impacts shows that plastic plates are preferred with regard to both aspects. In addition they have a very good signalling effect being produced in a bright yellow colour. Also deep digging can be effective taking into account costs and environmental aspects, but the risk reduction will according to literature be less than for the plates. Plastic plates are shown, in the literature surveyed, by full scale experiments to have at least as good, and sufficient, resistance to impact as concrete ones. This is verified by in-house numerical analyses. The finite element analyses show that the plastic plates deforms but do not break. The arching action of the backfill protects the buried pipe, and the stresses become only somewhat higher when using plastic plates instead of using stiff plates of steel or concrete. There may be unfavourable cases when the plastic plates cannot by themself stop forces and stresses passing down through soil layers acting on the buried pipe.
|
|
