Welding stainless steel: nickel, chromium 6 and the strictest limits
The rules, the limit values and the processes that require extra care
Introduction
Stainless steel contains chromium and nickel. When you weld it, they end up in the fumes, among other things as chromium(VI) compounds (chromium 6). The limit values for these substances are among the lowest in the whole list.
What the law says
Welding and thermal cutting in stainless steel and grinding in connection with them are listed in Annex 1 of the carcinogen executive order under Nickel. Annex 2 on welding fumes refers to it when the steel contains at least 0.1 % nickel. The requirements are the same as for other welding: you must have the training certificate (§ 16), and the work area must be delimited and signposted, including with no-smoking signs (§ 28). Polishing is not covered.
The numbers
| What | Limit value (mg/m³) |
|---|---|
| Chromium(VI) compounds, as Cr (8 hours) | 0,00025 |
| Nickel compounds, as Ni (8 hours) | 0.01 (respirable) or 0.05 (inhalable) |
| Total fumes for TIG in stainless and acid-resistant steel | 1,1 |
| Total fumes for manual metal arc welding in stainless and acid-resistant steel | 0,5 |
0.5 mg/m³ for manual metal arc welding in stainless steel is the lowest of the five process-related limit values. The executive order gives steels to SIS 2332 and 2343 as examples of stainless and acid-resistant steel. Chromium(VI) compounds are marked «K» for carcinogenic.
Compare with iron oxide, which has the limit value 3.5 mg/m³: chromium 6 must be kept 14,000 times lower.
The processes
- 01TIG in stainless steel: almost no visible fumes, but ozone and ultrafine particles. Use effective low-pressure extraction. If ozone escapes, you must use an air-supplied respirator or a respirator with an approved filter against ozone.
- 02Manual metal arc welding in stainless steel: fumes, but no ozone. Use effective low-pressure extraction. If it is not effective enough, you must also use an air-supplied respirator.
Courses and training
The AMU course «MAG-svejsning af rustfri stål proces 135 eller 136» (MAG welding of stainless steel, process 135 or 136; AMU 48748) lasts 5 days. According to AMU SYD's description, you weld 2-6 mm with process 135 and 5-10 mm with process 136. In the blacksmith programme, the stainless steel specialisation has the learning objective: «The apprentice can select and carry out joining methods for joining stainless materials, including automated welding in a repair and manufacturing process».