Hans I. Lange

Wear of Inconel 718 die during aluminium extrusion—a case study

Abstract The wear analysis of an aluminium extrusion die made of Inconel 718 alloy has been performed. The highest degree of wear was observed in the middle of the contact surface with no or little wear in the adjoining regions. The wear mechanism was similar to that for steel dies and consisted in adhesive and abrasive modes. Strong adhesion of aluminium to the die led to the formation of Ni–Al–Si–Mo–Ti–Cr–Fe–Zn–O compounds that, along with aluminium oxides, acted abrasively and resulted in considerable material removal after 40 extrusion cycles.

Burst Tests for High-Pressure Hydrogen Gas Line Pipes

Burst tests of line pipes containing high-pressure hydrogen and methane gas were conducted. The pipes tested were X65 ERW pipes with 267mm outer diameter and 6mm wall thickness. Applied pressures were 12 and 15MPa. A 300mm long crack was initiated by a shaped charge. Unstable shear fracture propagated at velocity of approximately 200m/s and then arrested. It was demonstrated that the arrested crack lengths were shorter in the hydrogen gas burst tests than methane gas burst tests. Pressure measurement indicated that decompression wave in hydrogen gas propagated faster than that in methane gas. This is the primary reason to the shorter arrested crack lengths for the hydrogen gas burst tests. The test results are discussed based on numerical analyses of gas decompression behaviors.Copyright

Full-Scale Burst Test of Hydrogen Gas X65 Pipeline

Full-scale burst test of X65 UOE linepipe, with 559mm outer diameter and 13.5mm wall thickness, pressurized at 16MPa by hydrogen gas was conducted. A 735mm long crack was introduced by explosive shaped charge over circumferential weld. The cracks were initiated and propagated in the both directions. The propagated crack lengths were 600mm and 270mm. J integral resistance curves were obtained from drop-weight as well as quasi static tests for the tested pipe material which was subjected to hydrogen charging. The tested steel showed little change in the resistance curves under realistic charging condition. Numerical simulation model of dynamic crack propagation, coupled with gas decompression behavior considering gas escape from opened crack, showed that an initiated crack was arrested at shorter distance in hydrogen gas pipelines than in methane gas pipelines, primarily due to earlier gas decompression in the former. The present results, together with the earlier full-scale burst tests conducted by the authors, demonstrated that hydrogen gas pipelines can be operated safely by using modern high-strength and high-toughness steel linepipes.© 2010 ASME

Engineering Critical Assessment of Thin-Walled Offshore Pipelines

Since the introduction of automated ultrasonic testing (AUT) in the late 1990s, acceptance levels for fabrication flaws in girth welds have in the main been established using fracture mechanics. The specific advice required for engineering critical assessment (ECA) where pipeline installation methods involve plastic strain, is already available in company specifications, and general standards and guidance. Although each subsea development is typically comprised of a number of pipelines with widely ranging functions, materials and geometry, the combination of small diameter and thin-wall linepipe is normally associated with MEG antifreeze pipelines and gas lift lines. In 2005, a thin wall was considered to be 9.9 mm while projects currently being engineered for installation in 2008–10 push the limit down to 6.9 mm. Despite the existence in some standards of a lower limit on pipe wall thickness below which ECA is no longer required — arguably 13mm in the case of DNV OS-F101 — assessments are nonetheless often performed for thinner-wall flowlines. Such analyses are required in order to provide case-specific confirmation of prescriptive workmanship-based acceptance criteria. These limits on fabrication flaws are not necessarily arbitrary and may originally have been derived from some form of general fracture mechanics study, although certainly not for thin pipes. Set against the backdrop of some recent projects on the Norwegian continental shelf (NCS), including Ormen Lange and Tyrihans, this study presents the background to the mechanical testing and assessment methodologies developed to overcome the challenges posed by thin-wall flowlines. Brittle fracture is not expected, either in the pipeline or during fracture mechanics testing, especially with constraint-matched single edge notched tension (SENT) specimens. This is primarily due to crack tip stress fields being dominated by plane stress conditions, more than is the case in thicker sections. The resulting material behaviour is characterised by ductility and is controlled by strength properties, not by fracture toughness. Specimen dimensions scale according to wall thickness and can be sufficiently small to make handling and testing difficult; the correspondingly small loads and attachment of instrumentation requiring specialised test equipment and laboratory procedures in order to obtain accurate and reproducible results. Pipes with low D/t values — typical for plastic strain installation — place even more stringent limitations on testing as specimen thickness is further restricted by pipe curvature. The paper covers the particular aspects of testing and analysis in the ECAs for installation we perform for thin-walled pipe. The estimation of crack driving force using finite element (FE) simulations is also discussed where important differences are noted between tolerable flaw dimensions from these and BS7910-based assessments. We even tentatively argue for the qualified use of existing fracture mechanics SENT data obtained on similar linepipe grades and weld procedures. Comparative evaluation can be made of material and weld tensile properties to ensure equivalence. Although WPQ testing, notched cross-weld tensile tests and segment testing are all that are required, limited fracture mechanics testing may also be performed to calibrate against the reference R-curves should further confidence be necessary.Copyright

Investigation of H13 Alloy Cutter Behaviour for Hard Rock Tunneling Applications

The current paper first analyzed the degradation mechanisms of the worn disc cutter made of forged H13 chromium alloy for hard rock tunneling applications. The paper investigated subsequently the mechanical properties of H13 to have a better understanding of the degradation mechanisms. Hardness tests were carried out on different positions on a cutter. Tensile tests and fracture toughness were carried out to investigate temperature effects. The test results showed that the material has a high wear resistance and a good temperature resistance, but its quasi brittle behavior and the residual stress effect (due to the cutting process) is critical for the chipping damage of the disc cutter.