Slip-On Flanges & the Gap tolerance between the flange & Pipe 1

[Naidooru1]

Hi guys,

Is there somewhere a guide on the tolerance for the gap between the slip on flange and the Outer Diameter of the pipe.
For all intensive purposes, this is a pipe shell vessel that was designed in accordance with ASME VIII Division 1, and this is one of the adjoining nozzles of an 864mm outer Diameter pipe.
If good engineering practice is used then the basics would be that it is as close as reasonably possible, centred around the pipe equally and with the required fillets further restricted by the values on the WPS.
But then you Get the "ENGINEER" that asks "why does he need to order a flange that is tight fit when he has and existing flange that is 22mm over the diameter of the OD of the PIPE measuring an ID of 886mm.
Please note further that ASME B16.47 does not have tables for Slip on flanges of this size and I have been to MSS-SP42 which moderately says that the flange must be interpolated from those in B16.5 to get a size and should involve a design for this flange. What would be the tolerance from here for the gap between the flange and the OD of the pipe?

Kind Regards
Ruben Naidoo
Senior Inspector of Pressurized Equipment

 

[DekDee]

Ruben,
The most important information you have left off is what standard was used for the manufacture of the engineers 886 mm ID flange.
34"pipe is 864 mm OD so as you have stated there is 22 mm gap.
My flange literature notes that slip on flanges greater than 600 NB are to be in accordance with BS 3293.
34" slip on flange to this standard has an ID of 869.9 mm which gives you a perfect fit,
Cheers,
DD

 

[racookpe1978]

22 mm excess mm in the diameter = 11 mm excess radius on the OD of the pipe.
The "intent" of the two standard fillet welds around a pipe joining a pipe and its slip-on flange does NOT include an 11 gap between the OD of the pipe and the ID of the slip-on flange arounf the OD of the pipe. .

 

[Naidooru1]

@ DEKDEE : The original code of Construction was ASME VIII Division 1 & the flange is an A105 flange. I might like to add that the original OD of the Equipment was 886mm but with the new sectional replacement taken out a few years back the re-design was cause to change the OD to 864mm. Now that they have come to replace the entire line the lager side Is now an issue.
still in respect to any flange that you construct above the 26 " size, what would be the deciding factor for gap tolerance between a pipe OD and a flange ID?

@ Racookpe: I agree with your sentiments as well, but it still boils down to one factor, what is the tolerance that we can live with if it isn't calculated then is the WPS sufficient as a tolerance or are there other deciding factors in determining the maximum space between the od of the pipe and id of the flange?

*Just a correction to my thread MSS-SP44 was referenced and not MSS SP42.*

 

[bimr]

This reference indicates maximum allowable is 3 mm at any position but sum of clearance on any diameter should not exceed 5 mm

[url=https://books.google.com/books?id=7JijBQAAQBAJ&pg=PA1-IA429&lpg=PA1-IA429&dq=slip-on+flange+pipe+clearance&source=bl&ots=OuHRGrbYXH&sig=p9Qj4kGHyhvKmRcNm5cEzPHfOQk&hl=en&sa=X&ved=0ahUKEwiDv9aFtqXKAhVK1B4KHaf2A-sQ6AEIWjAJ#v=onepage&q=slip-on%20flange%20pipe%20clearance&f=false]Mechanical Engineer's Reference Book[/url]

 

[Duwe6]

Have you looked at the incredible hours extra welding that will be required to weld up these grossly misfit flanges will take to meet ASME code? Now draw up a cross-section of this weld joint -- Guess What? this weld is now so huge that it is pretty certain to require PWHT - stress relief - due to the thickness.

My feeling in general is "Weld metal is better than base metal", so my tolerance on this would be generous, like 13mm gap all around. But look at the Fillet Weld fitup gap directions given in AWS D1.1. With that huge a gap, some kind of 'gap filler' like a rolled plate [a ring] should be looked at.

 

[rconner]

The "11mm" (or ~7/16/0.43 in.) gap figure, is of course calculated assuming the pipe and flange are perfectly sized to the stated dimensions, and further both are somehow held perfectly circular (and there is no accumulation of greater gap due to, differential thermal movements or stress relief of the welding process, restraint and sequence etc. [i.e. it may with such poor fit require a high degree of welder experience and craftsmanship indeed to achieve something close to this good?]

While not claiming specific relevance to your piping application or applicable code welding cylindrical pipes/tubes or flanges, you may be interested in "acceptable" fillet welding root opening (or gap) for structural welding in general, e.g. as noted in the AISC site e.g. at

https://www.aisc.org/DynamicTaxonomyFAQs.aspx?id=1878,

"8.3.8. What constitutes acceptable fit-up in fillet-welded joints?
From AWS D1.1:2004 Section 5.22.1, a root opening not exceeding 1/16 in. is permitted without modification. A root opening not exceeding 3/16 in. is generally permitted therein if the weld size is increased by the amount of the root opening or it is demonstrated that the required effective throat has been obtained. For plate thicknesses greater than or equal to 3 in., a 5/16-in. root opening is permitted if suitable backing is used." I think further a "3/16 in." (~5mm) figure is basically what is prescribed also e.g. for field-welding of large/thicker lap joints of steel water pipes per ANSI/AWWA C206 standard, that in Sect. 4.8.3 Lap Joint Assembly states , "Clearance between faying surfaces of lap joints shall not exceed 1/ 8 in. (3.2 mm) at any location for fillet welds on pipe having wall thicknesses less than or equal to 5/ 16 in. (7.9 mm), and clearance between faying surfaces of lap joints shall not exceed 3/ 16 in. (4.8 mm) at any location for fillet welds on pipe having wall thicknesses greater than 5/ 16 in. (7.9 mm). (see also Int'l discussion at bottom of file at

http://www.twi-global.com/technical...eptance-of-shape-imperfections-part-2-068/)."

and then later, "The fillet weld size shall be the specified thickness plus the root opening between the two overlapping plates. The finished weld shall create a 45° angle relative to the adjoining plates."

 

[StoneCold]

Why not use a weld buildup technique to fill in the required amount on the I.D of the flange. Then machine it clean. Then you have saved this massive flange and given your welder a gap that he can work with.

Regards
StoneCold

 

[rconner]

[Oops, I see I left out a concluding sentence I meant to include, "That being said, I suspect many welders will claim they can and have made "good" welds at greater gaps, and who knows some may have suitable "backing" (so to speak) for their claims, but in any case this appears at the very least to require a much larger weld volume and welding time."]