Which Weld Quality Level to Put on Your Drawing
ISO 5817 is the standard that decides whether a weld passes. It covers fusion welded joints in steel, nickel, titanium and their alloys, and it works by listing weld imperfections and giving a numerical limit for each one at three quality levels.
The levels are named, from tightest to loosest:
- B stringent
- C intermediate
- D moderate
Naming a level on the drawing is what turns “good weld” into something two parties can agree on.
What the levels actually control
The standard lists imperfections and sets a limit for each. Some of the ones that matter most in practice:
Undercut. A groove melted into the parent metal at the toe of the weld. It is a stress raiser. The allowable depth tightens as you move from D to B, and on level B for a dynamically loaded joint it is very restricted.
Excess weld metal and profile. How much the cap stands proud and how sharply it meets the parent metal. A steep toe angle concentrates stress, which is why the limit tightens at the higher levels.
Porosity. Gas trapped in the weld. Limited by individual pore size and by the total proportion of the area affected.
Lack of fusion and lack of penetration. Not permitted at level B, and restricted at the lower levels. These are the defects that actually cause structural failures.
Cracks. Not accepted at any level.
Misalignment. How far the two parts can be offset across the joint.
The point of the graded system is that a weld is not simply good or bad. It is measured against a level you chose.
What each level costs you
Moving from D to B is not a free upgrade. It changes:
Welding speed. Tighter profile and undercut limits mean more careful, slower work, more attention to weave and travel, and controlled interpass temperature.
Dressing. More grinding and blending to meet toe angle and excess metal limits.
Rework rate. The tighter the acceptance, the more welds get rejected and repaired. A repair is grind out, re-weld, re-inspect, and on a heavily welded part it puts more heat in and more distortion.
Inspection time. More measuring, more documentation, more back and forth.
None of that is padding, and the effect on a frame with hundreds of joints is substantial.
Apply levels selectively
This is the part most drawings get wrong. A single note saying “all welds to ISO 5817 level B” is easy to write and expensive to make.
A better pattern:
- Level B on the welds that carry the primary load, that are fatigue loaded, or that a code requires.
- Level C on secondary structure. This is the workhorse level for general fabrication.
- Level D on guarding, covers, brackets and anything where the weld just has to hold two pieces together.
Mark it per joint or per group of joints, using the tail of the weld symbol or a weld map. Saying “level C generally, level B on welds W1 to W6 per the weld map” takes one line and can move a quote significantly.
Static and fatigue loading
ISO 5817 distinguishes between joints under predominantly static loading and joints under fatigue loading, and some limits differ.
If your structure sees cyclic loading, a moving gantry, a press frame, a vibrating screen, say so. A joint that is fine under a static load can fail under millions of cycles at a stress raiser that level C would have accepted.
What ISO 5817 does not do
It is an acceptance standard. It does not tell anyone how to find the imperfections.
You still need to specify which inspection method applies to which welds and at what extent. Level B on a weld that only ever gets a visual check means level B on the things a visual check can see, which is not the same as a fully inspected weld.
It also does not specify how the weld is made. That is the welding procedure, covered in the WPS and qualification guide.
The three lines that belong on the drawing
- The quality level, per joint or per group, with the default stated.
- Whether the loading is static or fatigue.
- The inspection method and extent for the joints that need more than visual.
Three lines, and the quotes you get back become comparable, because everyone is pricing the same weld.
Send your drawing with the levels marked and we will match it with shops that work to them routinely.
Frequently asked questions
What is the difference between ISO 5817 and AWS D1.1 acceptance criteria?
They are two different systems that do the same job. ISO 5817 defines graded quality levels B, C and D with limits for each imperfection type. AWS D1.1 sets visual acceptance criteria in its own clauses, tied to whether the connection is statically or cyclically loaded. Use the one that matches the code your project is built to.
Is level B always the safest choice?
It is the most stringent, not the safest for your project. Applying level B to a whole frame raises cost and rework on joints nobody was worried about. The safe choice is level B on the joints that carry load and a lower level elsewhere.
Does the quality level tell the shop which inspection method to use?
No. ISO 5817 is an acceptance standard, not an inspection standard. It says which indications are acceptable. Which method finds them, and on which welds, is specified separately.
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