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Corrosion & Erosion Mapping

Corrosion and erosion costs industry millions every year; in various form which are as complex and diverse as the mechanisms at play.

Corrosion, although usually attributable to simple electrolytic, chemical or biological processes can be exacerbated by stress and temperature. It can be general or very localized in nature, progressive or aggressive and can occur in the most unexpected circumstances. Some of the most attritious forms of corrosion do not entail metal loss but seriously affect structural integrity. Erosion, through abrasion, can also assume various guises from general flow induced scouring through to localized damage caused by impingement or cavitation.

In isolation the two failure mechanisms are an important and expensive issue. In combination, their effects can be devastating. Reliable detection and accurate assessment is therefore of paramount importance - and as complex as the degradation mechanisms at play. No single inspection method can handle all the variables and, given the scale of the problem, any viable solution has to be selectively and appropriately administered.

Our philosophy is to use a Cause & Effect analysis approach to determine what we are looking for, where to look, what form it might take and which method(s) are most appropriate to give the best probability of detection.

For corrosion we focus our attention on vulnerable areas where process conditions are likely to induce attack; where liquid/liquid, liquid/gas and liquid sediment interfaces exist, in crevices and condensate settlement areas and where susceptible, dissimilar and sensitised materials may be exposed through coating or lining breakdown. For the effects of erosion we concentrate our attention on conditions where particulate matter (e.g. sand) is suspended in fluid; particularly in locations where flow pressure and volume is high and direction or turbulence may have a bearing, e.g. impingement opposite nozzles, elbow outer radii and where cavitation occurs around pumps, valves, etc.

We also consider the criticality and impact of what we are looking and the prime purpose behind what we are doing. The approaches used for a baseline survey, a risk based assessment and for planned monitoring are different. Only after these considerations have been made do we attempt to prescribe the optimum technique(s) for the task. These include -

• Automated ultrasonic corrosion mapping
• High resolution ultrasonic thro' wall imaging
• TOFD back wall profiling
• Ultrasonic OD/ID surface wave inspection
• Low emission radiography
• DPI, MP & EC surface micro-crack detection
• Remote field eddy current
• Remote visual inspection
• IRIS & eddy current tube inspection

Most of these techniques are inherently safe and non-invasive - so can be used 'on stream' with minimal preparation or disruption. Some can be remotely deployed and so reduce 'access' requirements.

These applicational benefits enable a pre-emptive approach to corrosion management and maintenance planning which, in turn, facilitates cost efficient shut down scheduling.

Also see -

- Coverage
- Depth Resolution
- Planar Resolution