Fitness For Purpose Assessment Research Articles

Fitness for Purpose Assessment of Girth Weld Defect Based on In-Line Inspection

The girth weld defect is one of the most common types of defects on oil and gas pipelines, which can have a strong impact on the operation safety. Several girth weld failure accidents have occurred on PetroChina’s pipelines in recent years. In this paper, PetroChina’s current work on inspection and fitness for purpose assessment of girth weld defects is summarized. The in-line inspection has been proved to be the best practice for oil and gas pipeline defect inspection, but there are still some technical issues such as defect characterization and parameter selection. Fitness for purpose assessment methods for girth weld defects include strength assessment method based on plastic collapse, FAD method based on both plastic collapse and fracture, simplified factor method and numerical analysis method based on finite element. It is critical to identify the actual type of defects detected in in-line inspection to select an appropriate assessment method. The identification of various loads and the selection of appropriate material parameters are also important issues in assessment procedure. The key techniques to be developed include defect characterization, load identification, assessment of defects on high grade steel pipes, reliability-based assessment, etc.

Climate Station Analysis and Fitness for Purpose Assessment of 3053600 Kananaskis, Alberta

Kananaskis climate station 3053600 provides a climate record from 1939 to the present. The operational history of the station and the changes in its location are reviewed. Since 1939, the station has been operated by several different organizations and located at three different sites compromising the use of the data. Further, the metadata for this station is both inaccurate and incomplete. The fitness of this data for trend and other applications is assessed. The differences in the series between locations suggest that studies should be confined to using the data from a single location, and users of the data should be aware of the ongoing changes in the physical situation at the present location.

Experimental Investigation of the Effects of Reverse Bending and Straightening Process on Carbon Steel Bars used for Civil Engineering Applications

This paper presents an experimental investigation of the effects of reverse bending and straightening process on the mechanical properties of a typical carbon steel bar used for civil engineering applications. Twenty four specimens each were used for the metallogarphy, microhardness and tensile tests. The investigation revealed that the reverse bending and straightening process has no significant effect on the bars’ through-thickness microstructure and hardness. However, the reverse bending and straightening process reduces the yield load, ultimate load, and displacement at fracture of the bars by 4.27%, 2.58%, and 18.62% respectively. These results highlight the need to take into consideration the effects of the previous loading history of the bars/wires, particularly the reduction in the displacement at fracture and consequently, the ductility of the bars/wires in the design and fitness for purpose assessment of components made from them, since the bars/wires could experience high strain during installation and in service due to overloads.

05/00691 Fitness for purpose assessment after an over pressure incident at Arapuni Power Station

05/00691 Fitness for purpose assessment after an over pressure incident at Arapuni Power Station

05/00166 Fitness for purpose assessment after an over pressure incident at Arapuni Power Station: Firth, D. et al. International Journal of Pressure Vessels and Piping, 2004, 81, (6), 471–479

05/00166 Fitness for purpose assessment after an over pressure incident at Arapuni Power Station: Firth, D. et al. International Journal of Pressure Vessels and Piping, 2004, 81, (6), 471–479

Fitness for purpose assessment after an over pressure incident at Arapuni Power Station

In December 2000 the wicket gates of Arapuni Unit G7 closed rapidly when a control arm separated from a shaft and the wickets were free to move. The unit had been operating under normal conditions at the time. The resulting overpressure pulse caused the lower portion of the penstock to become barrel shaped, and a longitudinal riveted joint partially failed. A significant amount of cracking was visible in the cast steel stay vanes and deformation had occurred at the rivets in the scroll case. A program of work was instigated to determine the cause of the failure, and its consequences, i.e. the pressures reached and what work was required to ensure that the unit was fit for reuse. The root cause of the failure was the design and fabrication of a control arm installed when the wicket gate control system had been modified. This control arm had two segments which clamped around a shaft. The clamping bolts used had seen a high residual bending load and cyclic loading. They failed in fatigue. The coating on the inside of the penstock and scroll casing was brittle and an assessment of the degree of craze cracking in the coating on tensile test specimens allowed an accurate method of determining the plastic strain that had occurred in the penstock, and hence the stress and applied pressure that occurred during the incident. The major issue was the condition of the stay vanes and the rivet holes in the scroll casing. The cracking in them was quantified by NDT inspection. Most of the cracks seen in the stay vanes were original casting defects that had not propagated during the overpressure. An engineering critical assessment was carried out in accordance with recognized international standards to determine the effects of defects under brittle fracture and overload conditions for a range of pressure conditions. An initial assessment was performed using conservative estimated values for the applied stresses and materials properties. The initial calculation indicated that the units were probably fit for purpose. Mechanical testing on samples taken from the stay vane casting and strain gauging during a proof pressure test was carried out. This allowed the calculations to be refined and the confidence in the result to be increased. A fatigue assessment was then carried out in accordance with the standards. The stay vanes and the scroll in the unit were shown to be fit for purpose without any modification and fatigue was not predicted to be a major problem. The unit was returned to service without any modification to the cracked stay vanes. An inspection procedure and regime was also defined to ensure the unit remains fit for purpose.