Prequalifed "As Detailed vs As Fitup"

Date 10-02-2012 21:41

I need to ask: did you take the open code book examination with API 1104 or AWS D1.1?

The question is relevant because it should have been covered by the D1.1 seminar and you would have had to answer a couple of questions on the examination pertaining to at least part of your inquiry.

"As-detailed" are the tolerances that can be utilized by the designer when detailing the groove preparations. As an example: if the detailer feels it would be beneficial to increase the groove angle to provide better access for the FCAW gun, he has the option if doing so within the ranges permitted by the "as detailed" parameters. The tolerances are added or subtracted from the nominal values listed in the tables of Figure 3.3 or 3.4.

The "as fit-up" tolerances are added or subtracted to the nominal or the as detailed dimensions listed by the welding symbol in most cases. If you have worked on the shop floor you know that it isn't uncommon for the fitters to cut the member a second time upon discovering it was cut too short the first time, so the "as fit-up" tolerances are rather generous.

The rationale behind a prequalified groove detail is that experience has shown they provide sufficient access for welding for most conditions. Where the nominal values are too restrictive the "as-detailed" tolerance provides more latitude, but still are capable of providing the welder with suitable access.

It is neither the inspector’s nor the welder's prerogative to apply the "as detailed" tolerances. That additional latitude is available exclusively to the detailer/designer.

The "as fit-up" tolerances are the tolerances that can be applied to the actual fit-up conditions of the groove. The tolerances are added to or subtracted from the parameters shown by the welding symbol. The joint is properly fitted provided the actual measured dimensions are within the "as fit-up" tolerances.

Best regards - Al

By 357max

Date 11-06-2012 16:44

Echoing Al & Quoting from the Visual Inspection Workshop Reference Manual ~ 3.6 Prequalified CJP Groove Welded Joints-Appendix III "...Two types of tolerance are seen. As detailed means as it appears on the working drawings, which in turn means that it has been approved by the designer or responsible engineer. As fitup means as the joint is assembled for welding. The role of welding inspector covers:
1. Verification that prequalified procedure dimensions, as drawn, are within the dimensional range, as detailed.

2. Verification that joints as assembled and ready for welding meet the dimensional requirements, as fitup.

The tolerances may be additive. It is possible to take the specified dimension and add both the detailers' tolerance and the fitters' tolerance. When taking the practical test, careful attention must be given to the wording of the question. If the question asks for a range of tolerance as fitup and detailed both tolerances are taken. If the question asks for the range of tolerances as fitup, only the fitters' tolerance is taken. If the question asks for the range of tolerances as detailed only the detailers' tolerance is taken. Take only those tolerances asked for in the question.

By ziggy

Date 11-06-2012 18:20

357 max says "The tolerances may be additive."

D1.1 Clause 3.13.1 states that fit-up tolerances may be applied to the dimension shown on the detail drawing. If the detail drawings indicate the "as-detailed" tolerances then the "As-Fit Up" tolerances can be added to those.

Some prequalified WPSs will indicate this tolerance "additive" in the joint detail.

ziggy