DNV DNVGL-RP-G103 [ Revised ]

This recommended practice is primarily intended for those with responsibilities in the planning, implementation and acceptance of vessel inspections. It is aimed at the inspection of welded vessels constructed from metals, and related items, fittings and connections associated with them. The document is equally applicable to forged/spun metal pressure vessels, which contain no welds, as well as storage tanks and large diameter pipelines.

Although not intended to be covered by this document, some aspects of this recommended practice may also be applicable to vessels manufactured from other materials and plant items other than pressurised equipment, in which case some of the general principles developed may well still apply.

The recommended practice provides guidance for:

1) determining when NII is appropriate in principle as an alternative to IVI or as a means of deferment of IVI

2) information requirements to plan for NII

3) defining the requirements for the NII method(s) to be selected

4) selecting methods that meet the requirements

5) evaluating the results of the inspection

6) documentation requirements.

The scope is limited by the following constraints.

— It is assumed that the date of the next inspection following NII will be determined in the same way as with any other inspection, based on sound engineering judgement and an understanding of the degradation rates and tolerance of the equipment to degradation. This recommended practice therefore makes no attempt to influence the timing of the next inspection, other than where the intended scope of the NII inspection has not been fully met or where it is used in support of deferment of a comprehensive inspection.

— No consideration is given to the relative cost of different inspection options and the guidance process considers technical issues only.

— The recommended practice is principally for application to pressure vessels

— The recommended practice does not address legislative requirements, which may in certain countries preclude the use of non-intrusive methods. The recommended practice considers only the technical aspects of the non-intrusive inspection planning process, and the user should confirm that any inspection plan derived using this document satisfies national legislative requirements.

— The recommended practice does not consider the impact of external degradation mechanisms, for which inspections are intrinsically non-intrusive and would be addressed by conventional assessment means.

It is also important to note that the recommended practice does not aim to comprehensively cover every aspect of planning an inspection by NII but rather seeks to provide structured guidance at key stages of the process. Although the document provides guidance on the general principles of non-intrusive inspection it is not intended to be prescriptive, and readers should assess each case point by point against their own criteria, using the document as a guideline. The recommended practice cannot and is not intended to replace sound engineering and commercial judgement by competent personnel.

It should be recognised that with any scheme of examination there is a finite probability of missing flaws or degradation which could lead to failure. This applies to both invasive and non-invasive inspection.