WRC 107 support lugs 1

[waliq]

Hi all,

I has been designing a support lug for a vertical vessel (outer diameter = 610 mm). Length (T/T) 4100mm, MOC: SA 240 316L.

However, I was checking the feasibility of support lugs to vendor in lieu of skirt support ( owing to bottom head inspection issues of using a skirt on such a small dia vessel)

However, my support lugs calculations gives me the following failure for test case

Pm (SUS) | 109.60 115.15 | Passed |
Pm (SUS+OCC) | 148.53 138.18 | Failed |
Pm+Pl (SUS) | 111.12 172.72 | Passed |
Pm+Pl (SUS+OCC)| 150.83 207.26 | Passed |
Pm+Pl+Q (TOTAL)| 148.76 345.44 | Passed

I have searched in WRC 107 and ASME sec VIII, Div2 regarding the calculations for SUS+OCC case but couldnt find formulas.

I need to know the parameters, these induced stresses are dependent upon.

 

[DriveMeNuts]

Your result appears to comply with UG-23(d) and End Note 15 from ASME VIII Div 1. (Apply a factor of 1.2× to the allowable stress)

It looks like it doesn't strictly comply with Div 2 design procedure of Div 2 Table 5.3. If you were to re-assess the stresses in accordance with Div 2 Table 5.3, you may find you get a similar result. (0.9P + 0.6W + 0.7E < S is similar to P + W + E < 1.2×S)

 

[JStephen]

By "parameters"- lug dimensions, shell/head thickness, repad dimensions and thickness, eccentricity of load from shell?

 

[waliq]

@Jstephen: I meant to ask the parameters that SUS and OCC Pm equation uses. I could not find the equation for it. I tried changing the repad thickness and dimension but this value does not change at all. I was wondering if there is any other parameter (apart from increasing shell thickness) to reduce this value. Moreover, these values are failing for test case only.

@Drivemenuts: Thanks!!

 

[TGS4]

May I suggest that you obtain a copy of WRC 107 yourself and evaluate the calculations yourself. This game of 20 questions gets old rather quickly...

 

[JStephen]

WRC 107 might actually be the updated version with a different number, but I forget what that number is.
WRC 107 and similar sources don't say anything about combining stresses, they just give you shell stresses at specific points corresponding to a particular applied force or moment. How those are combined together, or combined with operating stresses, etc, would be per the vessel code or the designer or programmer, but is not covered in 107.

 

[waliq]

@Jstephen: I did not find them in WRC 107. I had gone though it before posting it here. Well, if I look at UG 23 (d), it says that the for earthquake or wind loading combined with the loading of UG 22, the max permitted compression stress can be 1.2 times the compression stress as computed above in clauses a, b and c.

The only parameter, that causes this warning to vanish is increasing the shell thickness. But, i am not sure if it is a good idea to increase the shell thickness for a removing the warning for support lugs induced stress, and that too for test case?

 

[DriveMeNuts]

Clause 'a' is for tensile stress.

 

[JStephen]

It's hard to say without knowing all the details. But there might be an option to consider the repad, or not. Or an option to consider the repad for some loadings and not for others. There may be size limitations for the repad where if you're outside the limits, the repad is disregarded. There may be options to interpret the increased stress allowances in different ways. Regardless, if you have a repad but it makes zero change to any of the stresses, it's being disregarded for some reason, and that reason may be valid or not.

 

[waliq]

@Jstephen: The only way these induced stresses reduce is by increasing the shell thickness.
@TGS4: I did see the WRC107 copy but it did not say anything about them. If you know of anything of this sort in WRC107, please share the reference.