A Review of Nondestructive Examination Methods for New-building Ships Undergoing Classification Society Survey

Abstract

Classification societies require ship manufacturers to perform nondestructive examination (NDE) of ship weldments to ensure the welding quality of new-building ships. Ships can contain hundreds of kilometers of weld lines and 100% inspection of all welded connections is not feasible. Hence, a limited number of weldments are specified by rules of classification societies to be inspected on a sampling basis. There is a variation between the rules and guidelines used by different classification societies in terms of both philosophy and implementation which results in significant discrepancy in the prescribed checkpoints, numbers, and their locations. In this article, relevant sections of the rules of mainstream International Association of Classification Societies members are studied and potential ways of improving them are discussed. The authors have endeavored to make this study as comprehensive as much as possible. However, given the challenges of covering every single aspect and variable related to NDE in the classification societies' rules and guidelines reviewed here, the authors can only attempt to cover the key features. 1. Introduction Ship structures are joined with hundreds of kilometers of weld lines. The presence of weld in a structure potentially reduces the structure's fatigue life by means of introducing a discontinuity into the completed weld/parent material joint, and introducing residual stress; this could be further amplified by presences of defects inherent to the welding process. Rules, standards, and guidelines may require manufacturers to carry out certain procedures for enhancing weld's reliability, such as weld toe grinding to enhance weld profile geometry (and hence fatigue improvement), heat treatment to improve welded joint's toughness, and nondestructive examination (NDE) to detect weld defects. performing NDE for finished welds is the best way to find possible defects, and relevant rules require manufacturers to do so. However, only a sample of welds is subject to thorough NDE as it is unfeasible to carry out the same extent of detailed inspection on all ship weldments.