Tom,

ASME, sub parts of ASME, API, AWS, AWWA, ABS, Navsea, etc etc etc etc all have difference requirments. It may help to be more specific on the codes you work with.

Howdy!  I'm a government welder at PSNS, and here's what we go through:

1:  Fit-up inspections cover the material types and thicknesses, joint design including root opening, and the symbols on the joint members for the welders.  If the root opening is greater than 3/16", then the weld size must increase proportionally (fillets), up to 5/16" root opening.  Greater than 5/16" requires weld buildup.

2:  This one I'm unsure about.  For us, it is required by NavSea on our QC forms.

3:  The shop performing the fitup is required, usually the last shipfitter left standing in the drydock 10 minutes before end of shift!

4:  See #1.

A good 'fitter makes life great for the welder, a good welder can save a 'fitter's rear!

I throw my $0.02 in for how we do it here and most of the shops I have worked in.  AISC and D1.1 are governing codes fabricating buildings. 

We dimensionally check everything after fitting and before welding.  I am not aware of any code requirement saying what % to inspect and it doen't matter here because we check everything and would, regardless of the code requirement.  If I am going to put my name on it as being dimensionally correct, I am going to inspect it, not just trust the fitter.  Every person here, from me to the best fitter here makes mistakes occasionally.  So nothing fit by anyone is beyond being scrutinized.  Now saying that does not mean we pull a tape on every detail listed on a fabrication drawing.  Highest priority and most critically attention is paid to dimensions of connections (bolted and welded).  We want everything to fit correctly and make life easier on our erectors and save ourselves backcharges for repairs.  During this dimensional check, the weld joint fitup is also checked.  99% of our welds are filllet welds so this is relatively easy. Excess gaps and bearing locations requiring oversize welds are the biggest hits here.  CJP welds recieve higher attention from me.  We usually have someone (QC or another fitter at a minimum) check layout of critical oxy-fuel cuts in major members so they are not cut backwards for instance.  Lesser priority and critical attention is given to things like stiffener location and more minor cuts like copes, etc.  WPS variables are routinely observed and montored as I walk around.  It goes without saying that there is another hold point after welding for 100% visual weld inspection before going out the door to the coating/shipping department.

My primary job is QC so I perform the majority of these inspections whenever I am available in the shop (about 80% of my time spent here).  When on the floor performing dimensional inspections, I am often somewhat getting in the way of the fitter so that, whenever possible, a piece or a spread of pieces is ready to weld ASAP after fitting is completed.  I often catch errors in layout before a piece is tacked up so most fitters somewhat tolerate my intrusions.  But that said, a piece is held after fitting until someone, who is then responsible for the dim-check, releases it to be welded no matter how long that takes.  I am a one man QA/QC and Safety Department, so I can't see everything from receiving all the way to shipping.  Others must help in the various departments.  If I do not perform the dimensional inspection, then a foreman is responsible to perform the inspection and he becomes the inspector of record for thast piece should something not fit later.  The competency of this inspection, as it relates to weld fitup, has grown better over the years as I have educated other to what D1.1 says and have enforced its use.  Excess gaps, bearing, WPS and prequal dimensions (you mean we can't just burn/grind any angle and then weld it up?  No one will see it after its welded.) has improved greatly.  CJP welds are monitored and observed more diligently than the "usual" fillet welds.

Sorry for rambling so I hope this helps.

In my smallish fab shop, where we build mostly GSE for aerospace, and the QA program has been in limbo for a bit.  I just started here not too long ago, and as QA manager one of the millions of details I have to plan for is weld joint fit up and prep inspection.  Our process presently has parts inspected after cutting and shaping.  Our welders are their own fitters, and they are responsible for cleaning their own joints as well.  Since we look at the part after it's cut, I have been allowing my inspectors to wait until the part is tacked in place to inspect fit up.  However, this is not as effective as I would like; there are 3 of us and a dozen very busy welders, some of whom are more proficient than others.  So, in the end, I proposed that we add a fit up inspection to every weld operation.  It's work for the planner, but as we do milspec work to ISO, I think it will be well worth the time, especially when the QAR comes around!

As far as what to inspect:  I have been doing this in one capacity or another for some 20 years, and the first thing I always look at is cleanliness.  Then I move on to the proper joint dimensions: bevel, root face, lands, radius, root opening.  If all that looks good, I then check the item to print, double check all the ups are up, all the downs are down and critical dimensions.  It takes 5 minutes to lay enough weld to make for a day of rework.  As far as codes go, we work mostly to D17.1, section 8, which leads right back to 1.1 and 1.2.  We also do some 1.6 work.  Every single one has provisions for pre-weld cleaning and fit up (i.e. D17.1, 5.5 and 5.6).  Joint dimensions are usually determined by the drawing you're working to.  Most of our drawings reference whichever AWS spec the part falls under.

My two inspectors and myself conduct all inspections in all phases of fabrication.  We do not make these guys wait very long, and usually if they come to tell us they're ready, we go to look at it immediately.  If your QA can't support, then you may be having a welder sitting around with nothing much to do for however long it takes to get an inspector in. 

Personally, I believe that a fit-up and pre-weld cleanliness inspection is a valuable tool that can prevent problems later down the road.  Like I said, it takes a few minutes to make a day's worth of rework, and it's my job to keep that from happening.  Not only is it time and material, it's also you're boss' and your company's money flying out the window.