En Iso 13920-bf Site

For linear dimensions (length, width, spacing), the deviations are roughly ±1 mm for small dimensions, scaling up based on the nominal size.

Review Note: These values are generally achievable by a competent welder using standard fixtures without post-weld machining.

The standard uses a letter-code system to define four distinct tolerance classes. The code BF is actually a combination of two separate tolerance categories. en iso 13920-bf

The keyword "EN ISO 13920-BF" is a specific shorthand found on engineering drawings. Let us break it down:

Clarification: The official ISO 13920 does not list a class "BF." Instead, the correct notation on a drawing should be something like: "General tolerances: ISO 13920-B" or "ISO 13920 – Class B." However, in industry practice, "EN ISO 13920-BF" is widely used to denote Class B tolerances for general fabrication (F = Fabrication). For the purpose of this article, we will treat "BF" as Class B applied to welded fabrications (length, angle, flatness, and symmetry). Review Note: These values are generally achievable by

| Term | Standard | Meaning | |------|----------|---------| | EN ISO 13920 | ISO 13920 | General tolerances for welded constructions | | Class C, D, E, F | ISO 13920 | Tolerance grades (C finest → F coarsest) | | BF | ISO 9692-1 | Butt weld preparation with Backing + Flat root face | | EN ISO 13920-BF | Invalid combo | Likely means: Tolerance Class F + Weld prep BF |

| Tolerance | Class C | Class D | Class E | Class F | |-----------|---------|---------|---------|---------| | Linear (e.g., length) | ±1.5 | ±2.5 | ±4 | ±6 | | Flatness per 1000 mm | 1.5 | 3 | 6 | 12 | | Angular (mm/m) | 3 mm/m | 6 mm/m | 12 mm/m | 20 mm/m | Clarification: The official ISO 13920 does not list

On a technical drawing:

ISO 13920-BF
Tolerance class: CL-M (medium)
Backing: Removable copper backing
Process: 135 (MAG)

| Parameter | Requirement | |-----------|--------------| | Weld type | Butt weld, single V, or U with backing | | Backing location | Root side | | Backing material | Steel, ceramic, or permanent (specified separately) | | Dimensional tolerance | Class C (medium) or Class D (coarse) per EN ISO 13920 | | Inspection | Visual after backing, then after final weld |

This is the critical section for quality control.