Tack Weld Requirements – Danger

Are you working with high-strength steels or critical components?

According to SFS-EN 1090-2:2018, section 7 on welding:
"Arc welding of ferritic steels and stainless steels shall be carried out in accordance with the requirements and recommendations of EN 1011-1, EN 1011-2 and EN 1011-3 as relevant."

The SFS-EN 1011-2 standard, Chapter 13 states:

"Tack welds: It is recommended that the minimum length of a tack weld should be 50 mm, but for material thicknesses less than 12 mm the minimum length of a tack weld shall be four times the thickness of the thicker part. For materials with a thickness greater than 50 mm or a yield strength over 500 N/mm², consideration should be given to increasing the length and size of tack welds, which may involve the use of a two-run technique. Consideration should also be given to the use of lower-strength and/or higher-ductility consumables when welding higher-alloy steel."

This requirement may feel inconvenient in practice. When assembling heavy components, it often seems easier to start with small temporary tack welds. In Finland, these are sometimes informally referred to as hinge welds.

However, the warning is clear. Small tack welds may cause cracks.

Visual testing and penetration testing before final welding may sound sufficient, but in reality they are not. Cracks can form during the welding process itself. If no one hears or sees the moment a crack develops, it can easily go unnoticed.

Without ultrasonic testing, cracks may remain hidden beneath the final weld. They may only become visible later, when the structure is already in use. At that point, the result can be a serious problem or even a significant safety risk.

The video linked to this post clearly demonstrates how heat, high-strength steel and undersized tack welds together create a dangerous combination.

Extensive information and detailed studies on this topic have been documented by the ArcLess Academy team. The purpose of this post is to encourage every welding professional to understand their own processes and to recognize the risks involved.

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Ville-Pekka Arasmo

EveryWeld Oy