API 12F weld criteria

[Airarc]

In the Api 12f weld definitions it describes a double weld butt joint with a note stating it's equivalence can be achived with one side welded with complete penetration.
In section 5 it states all weld joints require welds on both sides.
Question I have would one side welding with complete penetration be allowed.
Any advice would be helpful.
Airarc

 

[chicopee]

Complete penetration would require a backing ring,so would that be acceptable if it is not removed?

 

[Airarc]

Thanks for the reply! I have ran some weld samples and achieved 1/16 to 1/8" root reinforcement without backing. This would not be acceptable to code?

 

[ledon]

This would be dependent on the contour you were able to achieve on the root reinforcement and the soundness of the deposited metal. assuming the SMAW process was used the potential for gas porosity, slag inclusion and undercutting would be the primary concerns. Control of technique and heat is more difficult and more critical when welding 100% penetration from one side only. If the backside is accessible I would recommended a double sided weld over a single sided. You don't have to depend on the welder's skill level as highly for proper performance.