Ultrasonic Inspection Of Underwater Fillet Welds

INTRODUCTION Underwater construction utilizing welding is becoming a standard practice in today's offshore operations. Extensive effort by many organizations to improve underwater welding to a level comparable with "land" welding is now finding regular application offshore. Many firms now offer "code quality" welding jobs at water depths to one thousand feet and deeper. Most common, however, is welding in depths to three hundred feet. Applications areRepairs to damaged structure or pipelines.Modification of existing structures or pipelines.Additions to existing structures or pipelines. Although welding demonstrations in pressurized water vessels, the natural waters of a Scottish Lock or a convenient piece of ocean show "code quality" welds to be possible, routine underwater welding is still subject to many variables which can influence the outcome of the operation and the resultant quality of the deposited welds. These variables range from the quality of the available materials to the mood of the relatively unsupervised underwater welder. Throw in the variables involved in a complex diving operation, and there is certainly room for concern on the part of the client. Many a field engineer has paced the decks of a rocking ship, diesel engines roaring, wondering just what the weld deposits looked like. The terse noncommittal tone of the welder's voice over a com box and the hasty assurances of the deck supervisor do little to defray concern and speculation. Clearly, surveillance of the installation and/or nondestructive inspection of the completed weld is desirable. Various methods of NDE are used underwater to establish the condition of welds and structures. Radiography is commonly used in dry habitat situations involving butt welds in internally dry tubular structures such as pipeline joints. Magnetic particle inspection is favored in the North Sea for weld inspection, but this bulky equipment is limited to evaluation of the surface and near surface areas of welds and structures. Ultrasonic inspection is used with varying degrees of success and skepticism. Ultrasonic inspection however, is versatile in, and enhanced by, the underwater envitonment. Most welds installed underwater are "fillet" welds as opposed to "butt" welds. This is by design since fillet welds are characteristically the easiest to install and the least sensitive to welder technique. Defective fillet welds, however, can in some cases lead to serious consequences depending on the structure and its environment. Ultrasonic inspection to detect the common welding defects in fillet welds has been given much attention by the author's firm. This paper will serve to impart to the knowledgeable reader, the techniques which we have developed for this method of inspection. The importance of visual surveillance during the welding is an important aspect of the subsequent ultrasonic inspection. This is demonstrated through a description of an underwater construction project in which these techniques were utilized.