Shipbuilding and marine fabrication
Weld monitoring for shipbuilding
High-volume welding under classification-society rules. The codes that apply, the four monitoring pain points that cost yards most, and which Therness signal addresses each.
ISO standard · reference card
ISO 13920: scope, tolerance classes and where it applies
Does ISO 13920 set the dimensional tolerance you are checking against? Scope decision flow for the general-tolerances standard for welded constructions, and the process controls that limit distortion.
- Designation
- ISO 13920
- Issued by
- ISO
- Title
- Welding — General tolerances for welded constructions — Dimensions for lengths and angles, shape and position
- Edition
- Confirm the edition your drawing or contract cites.
ISO 13920 answers a question a weld quality-level standard does not: is the finished structure the right shape, not just the right weld. It sets general tolerances for lengths, angles, straightness, flatness and squareness in welded fabrications, for use when the drawing itself has not stated a closer figure for that dimension.
The standard is a default, and treating it as anything else is the recurring error. A drawing dimension always overrides the general class; the general class exists precisely so a drafter does not have to tolerance every line on a fabrication drawing by hand. What the contract has to settle, in writing, is which tolerance class applies where the drawing is silent — leaving that unstated invites a dispute at final measurement rather than before fabrication starts.
The mechanism behind most out-of-tolerance findings is thermally driven distortion: angular distortion across a groove, longitudinal shrinkage along a long seam, bow across a panel. None of that is a defect in the weld itself in the ISO 5817 sense — it is a geometric consequence of how much heat went in, in what sequence, and how the assembly was restrained while it cooled.
Therness equipment does not perform dimensional inspection. It controls and records the process variables that drive distortion — measured heat input per pass, weld pool geometry through the run, and a traceable sequence record — so a dimensional nonconformance can be traced to a cause instead of argued about. See ISO 5817 for the separate question of weld acceptance, and the wire arc additive manufacturing entry for a process family where shape control from the process side matters even more directly.
Scope: does it apply to your job?
Applies to
- General linear and angular tolerances for welded fabrications, when invoked
- Straightness, flatness, parallelism and squareness of a welded shape
- Dimensions the drawing leaves unstated, taken by default from an agreed tolerance class
Does not apply to
- A dimension the drawing already states explicitly — the drawing tolerance always governs
- Weld imperfection acceptance, which a quality-level standard such as ISO 5817 sets
- Tolerances on features produced by machining after welding, not by the welding itself
Applicability decision flow
| Question | If yes | If no |
|---|---|---|
| Does the drawing already carry an explicit tolerance for this dimension? | Use the drawing's own figure. ISO 13920 is a default, not an override. | The general tolerance class agreed for the contract applies to that dimension. |
| Is the dimension itself produced by welding — a length, an angle, or the straightness of a fabricated shape? | It is in scope. | A machined feature produced after welding follows a machining tolerance standard instead. |
| Is the actual question weld quality — porosity, undercut, lack of fusion — rather than final dimensions? | That is ISO 5817 or the applicable quality-level standard, not this one. | Continue with the dimensional tolerance check. |
What proves conformity, and what only supports it
Conformity is decided by inspection and testing against the criteria the standard and the contract set. The records below are evidence that the process was held where it was qualified; they support an inspection result, they never replace one.
| Requirement | Record produced | Source |
|---|---|---|
| Holding heat input inside the qualified range that limits angular and longitudinal distortion on multi-pass work | Arc energy computed per pass from measured current, voltage and travel speed, not nominal figures | WeldTrace |
| Catching a bead geometry or sequence deviation before it accumulates into an out-of-tolerance fabrication | Continuous weld pool geometry captured through the full pass | PoolDrop |
Evidence the process, not just the paperwork
Therness records what the machine actually delivered on every weld — parameters, thermal signature and a per-weld trail — so a conformity argument rests on measurements instead of recollection.
