Underwater Inspections: Credibility And Technology

Abstract Both the demand for underwater inspections and the number of suppliers of these services have grown dramatically in response to such domestic legislation as the Outer Continental Shelf Lands Act Amendment and the OCS Orders based on this act. But as yet, there is very little codified guidance concerning procedures, documentation and qualification of inspection systems or personnel. Without sanctioned procedures it is, of course, difficult to certify inspection systems, and in the event of a structural failure, the assignment of responsibility may be all but impossible. Considering the high level of skill required to inspect tubular joints even on dry land one might certainly wonder whether uniform, approved procedures will ever be developed for use in the difficult underwater environment. The answer must almost certainly be "yes" since neither the offshore industry, nor the damaging effects of wind, waves, and corrosion are likely to vanish tomorrow. Developing standardized procedures for underwater inspections, and the hardware to do such inspections, has been a project under the sponsorship of the Director of Ocean Engineering, Naval Sea Systems Command. This work has aimed at such goals as repeatability, accuracy, reliability, etc. - in a word, credibility. In this paper, several techniques for improving the? credibility of underwater inspections are discussed. They implement the diver/ inspector team approach adopted by the Naval Coastal Systems Center in order to minimize the adverse effects of the underwater environment and the rapid turnover of Navy divers in anyone billet. In most applications a small computer has been used to ease the burden of inspecting "remote" locations, and in almost all cases, minor hardware design modifications have been made to improve signal quality. The combination of having massive amounts of data stored permanently by the computer and having a qualified nondestructive test specialist participate in inspections has resulted in well-documented, accurate, repeatable, and reliable inspections - in a word, credibility. Introduction Economic and legislated pressures on the offshore industry have, in the span of just a very few years, brought underwater inspection from an owner's prerogative to an absolute necessity. And the results of these inspections have come from a few snapshots or a casual debriefing to full color still and video documentation supplemented by nondestructive test reports. Along with the greatly expanded scope of underwater inspections comes the increased value of information gleaned by divers, manned and remote submersibles, and, of course, the temptation to use inspection results to plan or justify repair and maintenance actions. But with such a short track record the data produced by the more advanced techniques - ultrasonics and magnetic particle inspection - might not always be believed, though whether the fear is for costly false alarms or for the catastrophic potential of an undetected defect is a function of the specific case. Users of underwater nondestructive testing (U/W NDT) can see the credibility of this art/science improving-daily - that is to say it has been rather low in the not too distant past.