| 1. |
|
|
| 2. |
- Bergström, Gunnar, et al.
(author)
-
The influence from pipe surface, weld beads and protective skins on long term failure times for PE butt fusion joints
- 2004
-
In: Plastics Pipes XII.
-
Conference paper (peer-reviewed)abstract
- When making creep tensile tests on butt fusion joints in PE pipes almost all failures emerge from the outside of the pipe. Results indicate an influence from the outside surface on the long term behaviour of butt fusion joints. It is a well established practice to scrape the outside surface of PE pipes when making electro-fusion joints. This study stress the question if scraping or bead removal is a positive thing also when making butt fusion joints. Using PE100 pipes butt fusion joints were made using different levels of surface scraping before the butt fusion and with and without removing the weld beads before testing. PE-pipes with an outside PP or PE-skin were also included with and without the skin. Tensile test pieces were cut parallel to the pipe axis centered over the butt fusion joint. The long term strength evaluation were made using a standard accelerated test procedure with the test pieces exposed to a 5 MPa tensile loading immersed in 80 °C water with 2 % Arkopal N100 surfactant. With outside weld beads left intact failure times 200 h to 400 h are normal. Leaving the inner beads but removing the outer beads increase failure times to 1000 h to 2000 h. Failure times for test pieces without weld beads approach 10000 h. Scraping of the pipe surface to a depth of 0.2 mm did not substantially change the failure-time above that for an unscraped surface. Removing 0.7 mm from the pipe surfaceincrease failure times to 2000 h to 3000 h. Outside weld beads and outside pipe surface clearly interact to lower the time to failure in accelerated creep tensile tests. Weld bead removal and scraping of outside pipe surface significantly increase failure times. The exact mechanism is not clear and the implication on butt fusion joint performance in service is not demonstrated but the results indicate possible ways to enhance safety margins when making butt fusion joints. The topic will be given further attention in coming studies.
|
|
| 3. |
|
|
| 4. |
- Knudsen, Jette, 1961-, et al.
(author)
-
Trends in floral scent chemistry in pollination syndromes : floral scent composition in hummingbird-pollinated taxa
- 2004
-
In: Botanical journal of the Linnean Society. - London : Academic Press. - 0024-4074 .- 1095-8339. ; 146:2, s. 191-199
-
Journal article (peer-reviewed)abstract
- We studied an assemblage of 17 species of bird-pollinated Ecuadorian plants (from 14 angiosperm families), including taxa pollinated by short-billed (trochiline) and sickle-billed (hermit) hummingbirds. Hummingbirds are widely supposed to ignore fragrance while visiting flowers. We collected floral headspace odours in order to test the general prediction that specialist hummingbird-pollinated flowers are scentless. In nine out of 17 of these species we failed to detect any odours using gas chromatography-mass spectrometry (GC-MS), whereas the remaining eight species produced trace levels of volatile compounds. Most of these odour compounds were of terpenoid or lipoxygenase derivation and are commonly emitted by vegetative as well as floral plant tissues. Further studies will be required to determine whether these weak odours attract alternative pollinators, repel enemies or represent vestiges of a scented ancestry.
|
|
| 5. |
|
|
| 6. |
- Sällberg, Sven-Erik, et al.
(author)
-
Thermal Performance of Water Permeable EPS as Pipe Insulation
- 2004
-
In: 9th International Symposium on District Heating and Cooling.
-
Conference paper (peer-reviewed)abstract
- The purpose of this project was to study the function and strength of the EPSPEX pipe under unfavorable moisture conditions, in order to enable a comparison to traditional pipes. The EPSPEX pipe construction consists of cross-linked polyethylene (PEX) medium pipes placed in—and thermally insulated by—blocks of expanded polystyrene (EPS). The EPS blocks have a square-shaped cross-section and are laid directly in the ground with a polyethylene foil as only external protection. Laboratory tests were done on two different EPS alternatives: The standard density DC 200 and the lighter DC 100. These designations refer to the materials’ nominal compressive strength: 200 kPa and 100 kPa respectively. The pipes, laid in a watertight box backfilled with drainage shingle, were subjected to repeated flooding and drying. During the tests, the temperatures in both flow and return pipes were 80 ºC. The heat losses from the EPSPEX pipe increased after each repeated flooding and subsequent drying. The increase occurred at a diminishing rate and the insulation capacity recovered better if longer drying periods followed the floods. After four repeated floods and month-long drying periods, the heat losses had increased with approximately 40 % for the DC 200 alternative, and about 20 % for DC 100. During a final additional drying period the pipes recovered significantly. After this, the corresponding heat loss increase was about 20 % and 6 % respectively. The compressive strength of the EPS dropped somewhat during the tests, and a significant decrease in modulus of elasticity was seen.
|
|
