Dimensional tolerances of weld joints

[holdpt]

I have specifications that require welder testing to ASME sect.IX and welding by API 650. On this job, a 1/16" root opening for a fillet weld is called out but our trial fit is showing an average of 3/16" root opening. Not being as familiar with API 650 as AWS D1.6, I am questioning where joint dimension tolerances are addressed. I have been informed that it will refer you back to D1.6 but I have not found that statement either.

Thank you.

 

[fegenbush]

Per 9.2.1.1 of API 650, your welding tolerances must be in accordance with ASME Section IX and your Weld Procedure Specification (WPS) for tank welds and attachment to tank components. For welds on other assemblies, but not their attachment to the tank, it is permissible to comply with AWS D1.1, AWS D1.6, or ASME Section IX and your Weld Procedure Specification (WPS).

 

[holdpt]

Based on what 9.2.1.1 says, our 3/16" gap for the fillet weld (not attached to the tank) is acceptable per D1.6. API 650 and ASME sect. IX seem a little foggy when tolerances of joint design are questioned. Surprisingly, I noticed that sect. IX allows for no range in root opening for the GMAW/FCAW process, allowing only what the WPS would say I suppose.

Thank you for your assistance.

 

[weldstan]

Section IX does not address the issue. Joint design is a non-essential variable. The 1/16" gap is specified to mitigate cracking due to weld shrinkage and assure root penetration. Your 3/16" gap may well lead to poor root penetration (bridged root) which could well lead to failure in service, depending on the loads experienced.

 

[DekDee]

holdpt,
Where does the 1/16" root opening for fillet welds come from ?
The idea of a fillet weld is to have 0 root gap - codes usually stipulate a maximum root opening for the reasons given by weldstan.
Cheers,
DD

 

[gtaw]

1/16 inch root openings are acceptable per several structural welding codes/standards. Generally, when the root opening exceeds 1/16 inch, the weld size is increased by the root opening to compensate for the "loss" of effective throat caused by the presence of the root opening.

Best regards - Al

 

[DekDee]

Hi Al,
No problem with that - my comment was based on this statement - " On this job, a 1/16" root opening for a fillet weld is called out".
Why would you call for a root opening on a fillet weld ?
I realise socket welds have a gap to allow for weld expansion but structural fillet welds are normally clamped together prior to welding.
Cheers,
DD

 

[gtaw]

I use a 1/16 inch root opening when large multipass fillets are required. It provides a "release" mechanism for the residual stresses to reduce the probability of a root crack. I use "crush wires" that "crush" flat (reducing the root opening) as the weld cools and contracts in the transverse direction. By doing so, the transverse residual stress is accommodated and the root crack prevented.

Best regards - Al

 

[holdpt]

DekDee,
This is a door to a vessel. The re-pad going around the neck, left side and right side with FW in center, calls for 1/16" gap with a 3/8" fillet FW. Basically, the ID of the re-pad is 1/8 larger than the OD of the door neck. Rolling and breaking 1-1/4" 317L and 3/4" 317L made hitting this on the mark very difficult.
I do like the idea behind GTAW's use of a 1/16" gap on multipass fillets.