Acceptance limits to ISO 5817

Whether the imperfection you have just measured is acceptable — at quality level B, C or D, for the thickness in front of you.

Needed for excess metal and penetration
Leave empty if you only want the limit

The three levels

B is stringent, C intermediate, D moderate. The level is not chosen by the welder: it comes from the design, and it appears on the drawing or in the WPS. Pressure equipment and dynamically loaded structures normally call for B; ordinary static structures often accept C.

Most limits are proportional to the thickness with an absolute cap. Undercut at level C, for example, is 0.1·t but never more than 0.5 mm — so on 20 mm plate the cap decides, not the proportion.

What is never acceptable

Cracks and lack of fusion are rejectable at every level, with no measurement to argue about. That is the practical reason lack of fusion matters more than a bead that merely looks untidy: an ugly weld can pass, a weld with a crack cannot.

This is a reading aid, not the standard

The calculator covers the imperfections that come up most often in visual inspection. Where money or safety depends on the answer, the text of ISO 5817 decides — it has notes, exceptions and a wider list of imperfections than any calculator should pretend to reproduce.

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