Coil, tolerances and material verification

The start of the chain: the coil

Every LGS profile starts from a steel coil. Its properties:

• steel grade and nominal yield strength,
• nominal sheet thickness, with tolerance,
• type and amount of coating,
• width, which determines what section can be formed from it.

These are stated in the supplier’s material certificate. If the coil differs from what the design was based on, the structure is different — however similar it looks.

Why the tolerances matter

Thickness tolerance

Nominal thickness comes with a tolerance, and the coating is part of the total sheet thickness. The design has to make clear which value the calculation uses. This is not a formality: on thin sheet a few hundredths of a millimetre is proportionally a lot.

Geometric tolerance

The flange width, lip height, web depth and squareness of the produced section are all made to tolerances. The effective cross-section follows from them, so capacity depends on them directly.

That is why production checks profile length, dimple height and offset, flange and lip width, straightness and squareness. Quality control at the machine.

What verifies all this

From the product side

The profile’s declaration of performance and the CE marking: this states that the section was correctly produced from the coil and has the declared properties. What CE marking certifies.

From the production side

In-process measurements and their records. With digital quality control forms these attach to the project, so they remain traceable years later.

From the installation side

Verification of the installed product in the construction documentation. Incorporating a construction product.

The practical advice

Record which coil the structure was made from. This information is rarely needed — but when it is, nothing replaces it: after an incident, in a dispute or during a later investigation it is what links the installed material to its verification.

The point

The calculation works with nominal values, reality works with tolerances. The chain of verification is what connects the two — and that chain starts at the coil.