scope:

The determination of non destructive examination (NDE) acceptance criteria based on an engineering critical assessment (ECA) should be a balanced procedure based on the following elements influencing the integrity of the pipeline. a) Design of the pipeline related to the material, stress level during construction and service, probability on plastic deformation due to sagging, fracture toughness of the base metal, etc. b) Welding process defining properties of the welds such as level of (mis)matching of weld metal, fracture toughness of the weld and the heat affected zone (HAZ), type of typical welding defects, etc. c) Efficient welding process control essential for control of the mechanical properties of weld metal and the heat affected zones. This involves qualification to be used for qualification of welding procedures and welders and the quality control of the welding process parameters during production of the final pipeline. It is emphasised that the quality level depends on the sensitivity of the welding process for deviations with respect to production circumstances. d) NDE system required for the detection of all typical defects. A certain spread on the probability of detection (POD), false calls rate and the sizing accuracy is inevitable. The quality level of the NDE system has to be proven. The desired confidence level is 95 % for the specification of the POD and sizing accuracy related to all unacceptable defects. The performance of the NDE system must have a relation to the dimensions of the acceptable, i.e. NDE acceptance criteria. The appropriate mix of the sources of evidence for the determination of the acceptance criteria shall be judged separately for each particular job. These four elements are drawn in the flow diagram shown in figure 1 with their relation to the resulting acceptable defects in the pipeline.