Key issues and findings of corrosion specialist iicorr’s report include:
The typical age of platforms covered by the survey is 15-20 years – that is, within the normal design life of an offshore platform.
There is a broad range of approaches being used to monitor the integrity of caissons, with external visual inspection both above and below the waterline being used by all companies which responded.
The typical monitoring frequency of caissons is about every three years.
A total of 59 recorded integrity problems were identified, spread across a range of different problem types, by the five respondent companies over the past five years.
The biggest integrity problem affecting caissons is internal corrosion, leading to holes forming in the caissons. In this respect, it is interesting that the most used inspection technique is external visual inspection, which will clearly not detect pre-failure indications of internal corrosion.
Relating to the previous conclusion, in the case of one company, holes were detected on one occasion whereas neither internal nor external corrosion was detected, indicating that the inspection regime appeared to be ineffective at detecting serious integrity problems prior to failure.
An illustration of the potentially serious effects of integrity problems in caissons is that across only five companies in the past five years there have been six recorded incidents of complete severance of a caisson. Each of these incidents is a potential large dropped object, with the risk of significant subsequent damage to structure or hydrocarbon risers/pipelines below.
The responses demonstrate the significant consequences of caisson integrity problems, with 29 incidents overall reported ranging from caissons being out of service through to complete replacements being required.
Caisson integrity is viewed as a very significant issue for offshore platform operators.
iicorr makes five key recommendations:
The industry needs to recognise and rectify the design weaknesses that are resulting in failures of caissons before the end of their design life.
These improvements in design need to include measures to prevent internal corrosion and marine fouling as priority items.
Inspection, monitoring and mitigation effort, likewise, needs to be focused on the detection and prevention of internal corrosion and marine fouling.
The supply chain involved in the delivery of inspection, monitoring and mitigation solutions needs to develop improved technology which delivers more effective detection and prevention of caisson integrity problems.
Furthermore, asset owners/operators need to recognise the potential unplanned costs that caisson integrity problems cause to their operations and allocate inspection, monitoring and mitigation resources appropriately.
An iicorr says the industry in general needs to share knowledge and lessons learned from failures more effectively, to improve caisson integrity and therefore reduced unplanned expenditure.
iicorr’s specialist inspection services business unit manager, Tony O’Shea, said: “The results of the study are extremely valuable to iicorr and operators. They show that using appropriate inspection, monitoring and mitigating techniques to detect and prevent caisson integrity problems can deliver significant added value to asset operators.”
The caissons research is the first in a planned series of specialist surveys by iicorr.
They are designed to address particular issues and this first report would appear to highlight clearly the high cost of integrity issues and the savings that can be generated by stopping problems from happening in the first place. Moreover, the company has entered into collaboration agreements with a number of UK and international universities to share the knowledge it is collecting and collating. And it is looking at joint industry projects to encourage valuable research and help equip students with expertise of significant use to industry.
The report is available on www.centreofexcellence.com
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