Computational Modelling of Thermally-Induced Concrete Pavement Upheaval Buckling

The first buried hot bitumen (hotbit) pipeline is now operating successfully in the Alberta oil sands north of Fort McMurray and more are on the way. These hotbit pipelines are designed to transport raw, undiluted bitumen to a central refining plant at temperatures up to 140°C. They are constructed in winter when the ground is frozen allowing heavy construction equipment to travel across the watery muskeg terrain without sinking. Construction continues even when atmospheric temperatures fall as low as −30°C. Hotbit pipelines are buried with more than 1.2 m of cover, which can prevent them from expanding when they are heated from their locked-in installation temperature to their operating temperature of 140°C. Large longitudinal compressive stresses induced by this restrained thermal expansion combined with high hoop tensile stresses due to internal pressure produce stresses in the pipe wall that exceed the maximum allowable combined stress of 90%SMYS specified in North American pipeline codes (ASME B31.4 and CSA Z662). Two methods are available to handle these high combined stresses in hotbit pipelines. The first method is to expand the pipe during construction by preheating it to a temperature of approximately 90°C and then locking in the expansion by backfilling the pipeline trench before the pipe has had a chance to cool. By limiting the positive temperature differential between installation and operation to approximately 50°C, this method keeps thermally induced axial compressive stresses low enough that the combined stress does not exceed the allowable limit of 90%SMYS specified by pipeline codes. In the second method, the pipeline is still constructed in winter but without preheating. Temperature differentials and thermally induced axial compressive forces are much higher than in the first method and carefully engineered restraint is require to prevent the pipe from failing by pushing out of the ground at bends or by either lateral or upheaval buckling of long straight sections in muskeg swamps and bogs. This method requires strain-based design principles to show that, when the pipeline is first heated to its operating temperature, large thermally induced compressive stresses in the pipe wall are acceptable because they dissipate without causing failure when the pipe steel yields. Both methods are technically acceptable but require specialized pipeline engineering skills to implement them successfully. The first method incurs the cost of preheating and increased construction costs due to reduced pipe lay rates while the second method incurs the cost of more robust restraint systems, particularly at bends. Details of both methods are presented and discussed to determine which of the two methods has the least cost and the least risk.

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Morphologies of Nonadherent Al2O3 and Matching Substrate Surfaces

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010009587x ◽

1972 ◽

Vol 30 ◽

pp. 524-525

Author(s):

C. S. Giggins ◽

J. K. Tien ◽

B. H. Kear ◽

F. S. Pettit

Keyword(s):

Electron Microscopy ◽

Oxide Scale ◽

Oxidation Resistance ◽

Substrate Surface ◽

Morphological Features ◽

Thermally Induced ◽

Oxide Spallation ◽

Oxidation Resistant ◽

Induced Stresses ◽

Substrate Surfaces

The performance of most oxidation resistant alloys and coatings is markedly improved if the oxide scale strongly adheres to the substrate surface. Consequently, in order to develop alloys and coatings with improved oxidation resistance, it has become necessary to determine the conditions that lead to spallation of oxides from the surfaces of alloys. In what follows, the morphological features of nonadherent Al2O3, and the substrate surfaces from which the Al2O3 has spalled, are presented and related to oxide spallation.The Al2O3, scales were developed by oxidizing Fe-25Cr-4Al (w/o) and Ni-rich Ni3 (Al,Ta) alloys in air at 1200°C. These scales spalled from their substrates upon cooling as a result of thermally induced stresses. The scales and the alloy substrate surfaces were then examined by scanning and replication electron microscopy.The Al2O3, scales from the Fe-Cr-Al contained filamentary protrusions at the oxide-gas interface, Fig. 1(a). In addition, nodules of oxide have been developed such that cavities were formed between the oxide and the substrate, Fig. 1(a).

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Applications of ultramicrotomy for materials characterization

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100147004 ◽

1993 ◽

Vol 51 ◽

pp. 232-233

Author(s):

R.T. Blackham ◽

J.J. Haugh ◽

C.W. Hughes ◽

M.G. Burke

Keyword(s):

Materials Science ◽

Microstructural Analysis ◽

Analytical Electron Microscopy ◽

Austenitic Stainless Steels ◽

Specimen Preparation ◽

Preparation Technique ◽

Thermally Induced ◽

Radiation Induced ◽

Characterization Of Materials

Essential to the characterization of materials using analytical electron microscopy (AEM) techniques is the specimen itself. Without suitable samples, detailed microstructural analysis is not possible. Ultramicrotomy, or diamond knife sectioning, is a well-known mechanical specimen preparation technique which has been gaining attention in the materials science area. Malis and co-workers and Glanvill have demonstrated the usefulness and applicability of this technique to the study of a wide variety of materials including Al alloys, composites, and semiconductors. Ultramicrotomed specimens have uniform thickness with relatively large electron-transparent areas which are suitable for AEM anaysis.Interface Analysis in Type 316 Austenitic Stainless Steel: STEM-EDS microanalysis of grain boundaries in austenitic stainless steels provides important information concerning the development of Cr-depleted zones which accompany M23C6 precipitation, and documentation of radiation induced segregation (RIS). Conventional methods of TEM sample preparation are suitable for the evaluation of thermally induced segregation, but neutron irradiated samples present a variety of problems in both the preparation and in the AEM analysis, in addition to the handling hazard.

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Spin-crossover in an iron(iii) complex showing a broad thermal hysteresis

Dalton Transactions ◽

10.1039/d0dt03610b ◽

2021 ◽

Author(s):

Cyril Rajnák ◽

Romana Mičová ◽

Ján Moncoľ ◽

Ľubor Dlháň ◽

Christoph Krüger ◽

...

Keyword(s):

Schiff Base ◽

Schiff Base Ligand ◽

Spin Crossover ◽

Thermal Hysteresis ◽

Mononuclear Complex ◽

Hysteresis Width ◽

Thermally Induced

A pentadentate Schiff-base ligand 3,5Cl-L2− and NCSe− form a iron(iii) mononuclear complex [Fe(3,5Cl-L)(NCSe)], which shows a thermally induced spin crossover with a broad hysteresis width of 24 K between 123 K (warming) and 99 K (cooling).

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