Welding Fabrication Standards - EWF

Welding Fabrication Standards Page 48
Testing groups take into consideration manufacturing difficulties associated with different groups of
steels, maximum permitted thickness, welding processes, service temperature range and the
thickness by means of the joint coefficient of the governing joint (i.e. the full penetration butt joint
that, as a result of the weld joint coefficient, governs the thickness of the component). Table 1
reports the testing groups for steel pressure vessels.
The testing groups are numbered from 1 to 4 in decreasing levels of NDT. However, testing groups
1, 2 and 3 are subdivided into subgroups 1a, 1b, 2a, 2b, 3a, and 3b in order to reflect the better
behaviour to crack sensitivity of easy to weld low carbon alloyed steels and Austenitic stainless
steels.
As for testing group 4, it shall be applicable only for:
− Group 2 fluids 9 ;
− Ps ≤ 20 bar; and
− Ps ≤ 20 000 bar x L above 100 °C; or
− Ps ≤ 50 000 bar x L if temperature is equal or less than 100 °C;
− higher pressure test;
− maximum number of full pressure cycle less than 500;
− lower level of nominal design stress (according to EN 13445-3).
A single testing group is normally applied to the entire vessel. However, provided specific
requirements are met, a combination of testing groups is permitted.
Table 11 reports the main requirements for the testing groups.
In terms of quality levels for the welding imperfections, the overall philosophy has been the general
adoption of the following acceptance criteria:
− predominantly non-cyclic loaded vessels: ISO/DIS 5817:2000 quality level 'C'
− vessels subject to cyclic loading: ISO/DIS 5817:2000 quality level 'B'
9 According to the 97/23/Ce Directive, Group 2 fluids are non dangerous fluids (i.e. fluids other then
explosive, extremely or highly flammable or flammable, toxic and very toxic, oxidizing)
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