Lilley J.R.,Sonomatic Ltd.
Insight: Non-Destructive Testing and Condition Monitoring | Year: 2010
Code Case 2235 was originally issued by the American Society for Mechanical Engineering (ASME) Boiler and Pressure Vessel Code (B&PVC) Committee in 1996. Construction codes and standards are intended to ensure that pressure equipment and structures are designed, fabricated and tested to consistent quality standards in the interests of safety and reliability. The code cases carried the statement regarding qualification block(s) and shall contain a minimum of three flaws, oriented to simulate flaws parallel to the production weld's fusion line. Large numbers of technicians have been required by industry to work in accordance with the code cases and there has been a tendency to rush these through the certification process. It can also be concluded that, if applied in the spirit with which they are intended, the code cases can lead to a requirement for a large quantity of costly qualification blocks and high levels of qualification activity, which could have the potential to delay project timescales.
Stone M.,Sonomatic Ltd.
Insight: Non-Destructive Testing and Condition Monitoring | Year: 2011
Corrosion mapping, in which wall thicknesses over large areas are measured by 0 degree compression probe ultrasonics at closely-spaced points, is being used increasingly in oil and gas applications. This paper describes a new approach to statistical analysis based on wall thickness distributions derived from corrosion mapping data. The analysis methods developed are described and cumulative thickness distributions obtained in a wide range of field applications are presented. A range of situations in which corrosion of carbon steel is active are covered and the results include analysis of data from pressure equipment with CO2 corrosion, O2 corrosion, under deposit corrosion, naphthenic acid corrosion and corrosion under insulation. The results show that there are many situations in which the wall thickness distributions display strongly ordered behaviour. In many cases it is observed that the wall loss can be represented by an exponential distribution. Examples of wall loss distributions other than exponential are also provided. It is shown that the distributions established can be a useful basis for estimates for the uninspected areas when less than 100% coverage has been achieved. A summary covering applications of such analyses to integrity management practice is provided. This highlights the benefits of the use of underlying thickness distributions.
Benstock D.,Non destructive Evaluation Group |
Cegla F.,Non destructive Evaluation Group |
Stone M.,Sonomatic Ltd.
Journal of the Acoustical Society of America | Year: 2014
In corrosion assessment, ultrasonic wall-thickness measurements are often presented in the form of a color map. However, this gives little quantitative information on the distribution of the thickness measurements. The collected data can be used to form an empirical cumulative distribution function (ECDF), which provides information on the fraction of the surface with less than a certain thickness. It has been speculated that the ECDF could be used to draw conclusions about larger areas, from inspection data of smaller sub-sections. A detailed understanding of the errors introduced by such an approach is required to be confident in its predictions. There are two major sources of error: the actual thickness variation due to the morphology of the surface and the interaction of the signal processing algorithm with the recorded ultrasonic signals. Parallel experimental and computational studies were performed using three surfaces, generated with Gaussian height distributions. The surfaces were machined onto mild steel plates and ultrasonic C-scans were performed, while the distributed point source method was used to perform equivalent simulations. ECDFs corresponding to each of these surfaces (for both the experimental and computational data) are presented and their variation with changing surface roughness and different timing algorithms is discussed. © 2014 Author(s).
Cawley P.,Imperial College London |
Cegla F.,Imperial College London |
Stone M.,Sonomatic Ltd.
Journal of Nondestructive Evaluation | Year: 2013
There is increasing interest in the use of permanently installed monitoring systems to track the progress of corrosion. There is a choice between point thickness measurement systems, those that monitor the average thickness over a modest area, and large area monitoring systems that will detect relatively severe, localised corrosion. The relative merits of the different types of monitoring system are assessed for cases with different likely fractions of the total surface area affected by corrosion. If the wall loss is expected to be fairly uniform over the component surface then a small number of point sensors is the most attractive solution, whereas if the loss is likely to be highly localised at an unpredictable location and potentially severe, a large area monitoring system is most suitable. In the intermediate case of modest loss over a significant fraction of the surface, the choice is more complex. If the requirement is to detect relatively large wall loss that may be localised then the number of point sensors required increases substantially and the average thickness area monitoring systems appear to be more attractive. However, it is shown that corrosion distributions are frequently exponential, and this can lead to large maximum pit depths when the average wall loss is at the margin of detectability with current commercially available systems. © 2012 Springer Science+Business Media New York.
Osbeck S.,Robert Gordon University |
Osbeck S.,Sonomatic Ltd. |
Ward S.,Cytec Industries Inc. |
Idriss H.,Robert Gordon University |
And 2 more authors.
Applied Surface Science | Year: 2013
The adsorption properties of untreated, electrochemically treated and ultra-violet/ozone treated polyacrylonitrile based carbon fibres were investigated using temperature programmed desorption (TPD) on a series of linear alcohols as probes in order to understand its surface properties. Surface uptake was found to be sensitive to both the surface treatment and the nature of the adsorbates. Surface coverage increased with increasing alcohol chain due to the increase in their polarizability. It also increased with the level of surface oxygen of the fibres most likely because it facilitates the OH bond dissociation of the alcohol functional group. In addition, the desorption temperature (during TPD) tracked the surface oxygen levels (as determined from XPS O1s signal) suggesting increasing in the adsorption energy. The reactions of C1-C4 linear alcohols were also investigated on the surface of the fibre carbon. The main reaction was dehydrogenation to the corresponding aldehydes; the dehydration reaction to olefins was not observed. The dehydrogenation reaction was sensitive to the length of the alky chain. It was highest for methanol (to formaldehyde) and decreased with increasing the carbon number. Overall TPD of linear alcohols was shown to be a promising method for quantifying the level and strength of bonding occurring on carbon fibre surfaces. © 2013 Elsevier B.V.