Acceptance Levels

General

Defect acceptance levels are included in certain specifications - especially in application specifications. The tolerances are usually determined by the use of fracture mechanics, a subject which uses mathematical calculations and mechanical tests, in order to arrive at maximum defect dimensions permissible prior to remedial action.

Some specifications contain defect acceptance tolerances which are more strict than others, depending on the criticality rating of the structure or application to which the specification applies.

Overall criticality rating depends on a variety of factors including: the stresses involved, e.g. pipe pressures; the environment, e.g. contact with corrosive chemicals; erosion, e.g. from fluid flow.

The following list shows a variety of applications in a descending order of criticality:

1. Vessels and pipework for radioactive substances.
2. Pressure vessels welded to PD 5500 or the ASME boiler code.
3. Pipework welded to BS 2633.
4. Pipelines welded to BS 4515, API 1104, BGC PS P2.
5. Bridges, ships and general construction.