WRC 107 & 297

Topics 

Local Stresses in Spherical and Cylindrical Shells due to External Loadings- WRC Bulletin No. 107



Local Stresses in Cylindrical Shells Due to External Loadings on Nozzles-Supplement to WRC Bulletin No. 107

Boundary condition for using WRC 107 

d/D50 (Here, T=Vessel Thickness, Dm=mean diameter of vessel, d= O.D of nozzle)

Boundary condition for using WRC 297 

d/D=20   and d/t=20   and D/T=5



Nozzle must be isolated (it may not be close to a discontinuity) – not within 2√(DT) on vessel and not within 2√(dt) on nozzle

Difference between WRC 107 and 297 •

1. WRC 107 calculates only the vessel stresses while WRC 297 calculates Vessel stresses along with nozzle stresses.

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2. WRC 297 is applicable only for normally (perpendicular) intersecting two cylindrical shells whereas WRC 107 is applicable for cylindrical as well as spherical shells of any intersection.

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3. The attachments for WRC 297 checking must be hollow but WRC 107 analyzes cylindrical or rectangular attachments which can be rigid or hollow.

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4. WRC 297 is not applicable for nozzles protruding inside the vessel (Fig 1), Tangential Nozzle (Fig2), Nozzle at angle (Fig 3).

Difference between WRC 107 and 297 •

5. Typically, WRC-107 is used for local stress calculations and WRC-297 is used for flexibility calculations.

Limitations of WRC •

1. Neither bulletin considers shell reinforcement nor do they address stress due to pressure.

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2. CAESAR II ,PVElite & CodeCalc will not extrapolate data from the charts when geometric limitations mentioned above are exceeded. Extrapolated data may not be appropriate.

Torispherical Heads

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Torispherical heads are made of a dish, with a constant radius.  Joining the dish directly to the cylindrical section of the vessel would lead to a rapid change in geometry, resulting in excessive local stresses.  To avoid this, a transition section (the “knuckle”) is used between the dish and the cylinder.

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The weakest section of the vessel is usually the knuckle.  The vessel pressure rating can be increased by thickening the knuckle, making it more expensive.  Normally, torispherical heads with pressure ratings much above 10 bar are uneconomic.

Torispherical Heads

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To define the head geometry, the following dimensions are required:

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–  Radius of the dish head, R – typically this is the same as the diameter of the vessel, D.

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–  Radius of the knuckle, r – typically this is in the region of 6% of the vessel diameter, D.

Ellipsoidal Heads

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For pressures over 10 bar, ellipsoidal heads are often used.  In cross-section, the head resembles an ellipse, its radius varying continuously.  This results in a smooth transition between the dome and the cylindrical part of the vessel.  Ellipsodial heads are deeper than comparable torispherical heads.

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The shape of the ellipsoidal head is defined by the ratio of the major and minor axis.  A standard arrangement on vessels is the 2:1 elliptical head (see Figure 2).  This will have a depth of head which is a quarter of the vessel’s internal diameter, D.

Ellipsoidal Heads