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| 2. |
- Bergström, Gunnar, et al.
(författare)
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Acceptanskriterier för repor och intryck i plaströr Accpetance criteria for scratches and indentations in plastic pipes
- 2009
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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.
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| 3. |
- Bergström, Gunnar, et al.
(författare)
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Accpetance criteria for scratches and indentations in plastic pipes
- 2009
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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.
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| 4. |
- Bergström, Gunnar, et al.
(författare)
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Does sickness presenteeism have an impact on future general health?
- 2009
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Ingår i: International Archives of Occupational and Environmental Health. - Berlin : Springer. - 0340-0131 .- 1432-1246. ; 82:10, s. 1179-1190
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: The primary aim of this prospective study was to investigate whether working despite illness, so called "sickness presenteeism", has an impact on the future general health of two different working populations during a follow-up period of 3 years.METHODS: The study was based on two bodies of data collected at a number of Swedish workplaces from 1999 to 2003. The first material comprised 6,901 employees from the public sector and the second 2,862 subjects from the private sector. A comprehensive survey was issued three times: at baseline, after 18 months and after 3 years. Apart from the explanatory variable sickness presenteeism, several potential confounders were considered. The outcome variable was good/excellent versus fair/poor self-reported health.RESULTS: Sickness presenteeism at baseline was consistently found to heighten the risk of fair/poor health at both the 18-month and 3-year follow ups even after adjusting for the detected confounders.CONCLUSIONS: To the best of the authors' knowledge, this study is the first to show that sickness presenteeism appears to be an independent risk factor for future fair/poor general health.
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