650-XXX
Title: /
Shell Manhole Cover & Flange Thicknesss, Table 5-3
Date: / Aug 6, 2013Contact: / Name : Jamie Marchitello
Company
Phone : 8215-356-6835
E-mail :
Purpose: / To provide mathematical equations for calculating thickness of Manhole Cover plate and Bolting Flange valid for all listed sizes of manholes and for all design liquid heights.
Source: / B Mistry
Revision: / 0
Impact: / The business impact of this item is neutral.
Rationale: / API-650 provides only Tabulated Values in Table 5-3 for thickness of Shell Manholes Cover Plates and Bolting Flanges and only for listed design liquid heights. Basis of Tabulated values have not been disclosed. Tabulated values are not much of use for computrized design or tanks with design liquid height exceeding shown in the table 5-3. Also, thickness of cover plate and bolting flange is not directly proporsional to design liquid height. Thicknesses are proportional to squar root of design pressure(design liquid height). Using interpolation between any design lliquid hight will result in thickness which is not technically correct.
This agenda item provides an equation to calculate Manhole Cover and Bolting Flangesthickness that are valid for any design liquid height (desin pressure).
Derived Equation is shown in detail and has been verified against the Tabulated values.
Equation is provided in dimessionless and transparent form.
Calculated values are all within +/- of values shown in Table 5-3 which have been rounded up.
Proposal:
(Changes in Red) / Revise 5.7.5.1, add 5.7.5.6, correct Table 5-3 and add foot note “d”.
5.7.5.1 Shell manholes shall conform to Figures 5-7A and 5-7B and Tables 5-3a through 5-5b (or Tables 5-6a through 5-8b), but other shapes are permitted by 5.7.1.8. In lieu of tabulated values of thicknesses shown for Cover Plates and Bolting Flange, calculated values using equations in 5.7.5.6 are also acceptable. Manhole reinforcing plates or each segment of the plates if they are not made in one piece shall be provided with a 6 mm (1/4 in.) diameter telltale hole (for detection of leakage through the interior welds). Each hole shall be located on the horizontal centerline and shall be open to the atmosphere.
5.7.5.6
Nominal thickness of cover plates and bolting flange of shell manhole shall be not be less than determined by the following equations.
In SI Units
Where:
Nominal Thickness of Cover Plate (mm); (inch)
Nominal Thickness of Bolting Flange (mm);(inch)
d= Bolt Circle Diameter in (mm); (inch)
H= Design Liquid Level, m (ft.) per 5.6.3.2
G= Specific Gravity of Stored Product not less than 1.0
C = Co-Efficient for Circular Plates= 0.3
γ = Water Density Factor; SI 9.81/1000Mpa/m; USC 62.4/144psi/ft
Sd= Design Stress= 0.5 Sy: Mpa (Psi)
Sy= Built in Yield Strength; SI 205 Mpa; USC 30000 psi
Note: Low built in yield strength is deliberate & intentional to provide leak tight bolted joint, limiting deflection.
CA= Corrosion Allowance (mm);(inch)
Example: (USC) using 75.1ft tall tank with 20in manway.
0.6697in
Example: (SI) using 22.9m tall tank with 500mm manway.
17.1mm
Add Foot Note d, In Table 5-3
d In lieu of tabulated values of thicknesses shown for Cover Plates and Bolting Flange, calculated values using equations in 5.7.5.6 are also acceptable.
Correct Thickness of Cover Plates and Bolting Flange in Table 5-3 for Height 22.9 m(75.1ft.). They do not agree with calculated values for some cases as shown in Red for US Customary Units validation. (next page)
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