Flange welds, slip-on flanges

[JStephen]

Two questions have been bugging me about the little detail in UW-21 (ASME B&PV Code Section VIII Part 1) and the similar details in Figure 2-4. I think I asked these long ago, but don't recall ever seeing a definite answer, either.
For that inside fillet, is corrosion allowance supposed to be added to the throat dimension?
And, for either fillet, is there any requirement to increase the fillet depending on the weld gap size?
And perhaps more importantly, is anyone aware of any reference that actually answers these items? Seems this SHOULD Be in the code, but I'm not finding it anywhere. I find some provisions in AWS D1.1 and AWWA C207, etc., but not here where I need it.
I assume "nominal" thickness of the pipe is as-built thickness (or is this wrong?), so adding CA can in some cases make the fillet bigger than will fit in there.
On larger flanges, the weld gap details as 1/8" prior to the inclusion of any tolerances.
The software I normally use assumes "not" in both cases, so it can show a 1/4" fillet over a 1/8" gap even when a corrosion allowance is specified.

 

[r6155]

1) Obviously corrosion shall be added in the inside fillet weld
Asme VIII Div 1 UG-16 (e) Corrosion Allowance in Design Formulas. The dimensional symbols used in all design formulas throughout this Division represent dimensions in the corroded condition.

2) If the gap is within tolerance, nothing needs to be corrected.
Also see Appendix 2: c = basic dimension used for the minimum sizing of welds equal to tn or tx, whichever is less

Good information of GAP in PD 5500.

Regards

 

[JStephen]

Thanks, r6155.
Agreed with adding the CA- the issue is that in small pipe sizes (2" Sch 160 with 1/8" CA), you get a fillet weld that won't fit on the pipe doing that. Also, the tn already includes a CA, so if that controls the sizing, you get the CA in there twice.
On the gap-within-tolerance, I wasn't able to find a tolerance anywhere.
Edit: I did find this old interpretation on 2-4:

https://cstools.asme.org/Interpretation/InterpretationDetail.cfm?TrackingNumber=7708

VIII-1-83-31
Question(s) and Reply(ies):
Question: Is the minimum throat thickness of 0.7c as referenced in sketch (8) of Fig. 2-4 intended to be calculated in the corroded condition?
Reply: Yes.

 

[r6155]

My comments

a) GAP SORF class 150
GAP max = ((bore of SORF + tolerance ASME B16.5) - (OD pipe – tolerance ASME B16.10) /2

((61,2 + 1)- (60.3 – 0,8)) /2= 1,35 mm

U-5 TOLERANCES
The Code does not fully address tolerances. When dimensions,
sizes, or other parameters are not specified
with tolerances, the values of these parameters are considered
nominal, and allowable tolerances or local variances
may be considered acceptable when based on
engineering judgment and standard practices as determined
by the designer
b)
1)NPS 2 sch 160 tn= 8,74 mm
2)Suppose required thickness for pressure is = 0,5 mm
3)tx 0,5mm x 2 = 1mm but not less than 6 mm Then tx= 6 mm
4)c= the lesser of 8,74 mm and 6 mm Then c= 6 mm throat 0,7 x 6 = 4,2 mm
5)Throat = 4,2 mm + 3 mm C.A. = 7, 2 mm fillet leg = 1,41 x 7,2 = 10, 9 mm
6)10,9 mm > 8,74 mm + 1 mm (nominal GAP) = 9,74 mm EXCEEDED.

Also consider pipe undertolerance 12,5%

Appendix 2 2-1(b) All calculations shall be made on dimensions in the corroded condition

Some specifications require Welding Neck up to NPS 2 inclusive

I hope it helps you

Regards