Non-Probabilistic Failure Assessment Methodology About Titanium Pipes With Cracks

In this paper, the non-probabilistic failure assessment method for a pipe with crack was proposed, and interval model was applied in this assessment method. Compared with the deterministic approach, the assessment parameters were regarded as interval parameters in the non-probabilistic method, which could reflect the uncertainty of data and avoid the unsafety of results caused by the scatter of these parameters. On the other hand, compared with traditional probabilistic method, the non-probabilistic method only needs the range or bound of the parameters rather than detailed statistics information of the parameters which may be uneasy to be obtained from practical engineering. So the new assessment method reduces the request for detailed statistics properties of parameters. In this paper, load, material mechanical properties and the size of crack were treated as interval parameters, and the non-probabilistic failure assessment method was established based on the level 2 normal assessment of the BS 7910:2005. In this case, the assessment point (Lr, Kr) is not a deterministic value, Lr and Kr would vary in a certain interval. As a consequence, the assessment point was changed into a rectangle zone, and the non-probabilistic failure measure for pipe with crack could be obtained by the variation of the rectangle. The non-probabilistic failure measure can be defined as the ratio of the area of failure region to the total area of the rectangle. At last, the non-probabilistic failure assessment method was used to evaluate a titanium pipe, and the analysis results were compared with the results of deterministic method, probabilistic method according to Monte-Carlo and partial safety factors method, respectively. The analysis results sufficiently demonstrated that the new non-probabilistic failure assessment method proposed in this paper was feasible and available.

Direct Measurement of Titanium Pipe Diffusion Coefficients in Sapphire

The diffusion behavior of Ti3+ along basal dislocations in sapphire has been investigated by SIMS technique. High-density unidirectional dislocations were introduced by the high-temperature mechanical deformation, and Ti3+ ions were subsequently diffused along the dislocations. The SIMS diffusion profiles clearly showed diffusion tail due to the short circuit diffusion along the dislocations called pipe diffusion. Lattice diffusion coefficient and pipe diffusion coefficient of Ti3+ at 1300°C were measured to be 1.0±0.2×10-19 [m2/sec] and 2.0±0.6× 10-13 [m2/sec], respectively.

Fatigue Strength of Titanium Riser Welds: Effects of Material Grade and Weld Method

MARINTEK in co-operation with Institute of Energy Technology (IFE) has carried out a Joint Industry research programme Titanium Risers and Flowlines. The programme consisted of five sub-projects: Design, corrosion, welding, mechanical characterisation and fatigue. The primary results from the programme has been published in a Handbook (1999). The objective of this paper is to report on some of the results from the fatigue sub-project. Girth welded joints from a supplier of titanium pipe were fatigue tested in air. Pipe was welded by the TIG process, in 1G and 5G positions, with ASTM Grade 28 and 29 pipe material. Constant amplitude SN data were obtained. The results were compared with current proposals for fatigue design curves for titanium riser welds.