Deep penetration fillet weld
Applied to joint
T-joint — fillet welds both sides
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Wire for fillet welds
ER70S-6 and flux-cored options commonly used for structural T-joints.
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Description
A fillet weld where a specific welding process (typically submerged arc or deep-penetration MIG) achieves greater root penetration than a normal fillet. The increased penetration is accounted for in the design throat thickness using the 's' prefix in ISO notation.
In plain English
A normal fillet weld melts into the root a little bit, but a deep penetration fillet -- usually done with submerged arc (SAW) or spray-transfer MIG at high amps -- drives much deeper into the root. ISO lets you take credit for that extra penetration using the 's' prefix, which means the actual throat is bigger than the geometric 'a' throat. This means you can specify a smaller leg size and still meet the design throat. AWS does not have a direct equivalent symbol -- you would just call out the effective throat.
Symbol position
Fillet triangle on the reference line with 's' prefix dimension.
Size notation
ISO: 's' prefix indicates the deep penetration throat thickness (measured from root of penetration to face). 'a' is the standard geometric throat. 's' > 'a' when deep penetration is achieved.
Notation examples
ISO-specific concept. AWS handles penetration beyond the root through effective throat calculations but does not have the 's' prefix notation. When converting ISO drawings with 's' dimensions to AWS, the effective throat must be recalculated.
No direct equivalent. AWS uses 'effective throat' which can account for penetration beyond the root on certain joint geometries, but this is handled differently than ISO's 's' designation.
The 's' prefix indicates the deep penetration throat. Requires proven penetration via procedure qualification. The difference between 's' and 'a' represents the additional penetration depth.
Common uses
- Submerged arc fillet welds on structural steel
- High-deposition automated MIG/MAG fillet welds
- Joints where smaller visible leg size is desired with full design throat
- Cost optimisation on high-volume production welding
