Can anybody hear the crickets.....

DWCO

On the project the Engineer of Record ( the person who signs off on the calculations for the structure)should determine which welds are what class if required.
Here is how the specs inform the contractors

Just my ¢¢'s

Good Luck
Marshall

Here is part of a specification that was part of a recent project we did.

1.2 DEFINITIONS
Definitions of welding terms are in accordance with AWS A3.0. The
following classifications Class 1 (highest class) to Class 6 (lowest class)
indicate the project's class(es) of weld joints.

1.2.1 Class 1 Weld Joints
This covers complete penetration weld joints only. These weld joints apply
where failure would cause a loss of the system and/or be hazardous to
personnel. Class 1 weld joints are highly stressed (dynamic and cyclic
loading) and characterized as a single point of failure with no redundancy
for the redistribution of stress into another member.

1.2.2 Class 2 Weld Joints
This covers both complete and partial penetration groove weld joints and
fillet weld joints. These weld joints apply where failure would reduce the
overall efficiency of a system but loss of the system or a hazard to
personnel would not be experienced.

1.2.3 Class 3 Weld Joints
This covers both complete and partial penetration groove weld joints and
fillet weld joints. These weld joints apply where failure would not affect
the efficiency of a system nor create a hazard to personnel. Class 3 weld
joints are connections of secondary members not subject to dynamic action
and/or low stressed miscellaneous applications.

1.2.4 Class 4 Weld Joints
This covers weld joints applicable to welding reinforcing steel to primary
structural members.

1.2.5 Class 5 Weld Joints
This covers weld joints applicable to welding concrete reinforcing steel
splices (prestressing steel excepted), steel connection devices, and
inserts and anchors required in concrete construction.

1.2.6 Class 6 Weld Joints
This covers plug and slot weld joints as applicable to the requirements of
the project's code(s).