8/1/13 A Blog for Process Piping Engineering Professionals around the world: Step by Step Methods for WRC 107 and WRC 297 Checking in Caesar II

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This blog is developed with an aim of helping numerous piping design/engineering professionals from oil and gas, refinery, petrochemical field.

Monday, 29 July 2013

Introduction:

Whenever Pressure Vessel or Heat exchanger (Static Equipments) nozzle loads exceeds the allowable values

provided by Vendors (Equipment manufacturer) or standard project specific tables (guidelines), the piping stress

professional is permitted to use WRC 107/297 (or any other FEA) to check the stresses at the Nozzle-Shell

junction point and check the stresses with allowable values provided by Codes. If the stresses are found to be

within allowable limit then the load and moment values can be accepted without any hesitation. However there

are some boundary conditions which must be met before using WRC. This small write up will try to explain the

required details for performing WRC 107 and WRc 297 using Caesar II and step by step method for performing

WRC check.

Both deal with “local” stress states in the vicinity of an attachment to a vessel or pipe. As indicated by their

titles, WRC-107 can be used for attachments to both spherical and cylindrical shells while WRC-297 only

addresses cylinder to cylinder connections. While both bulletins are used for nozzle connection. WRC-107 is

based on un-penetrated shell, while WRC-297 assumes a circular opening in vessel. Furthermore, WRC-107

defines values for solid and hollow attachments of either round and rectangular shape for spherical shells but

drops the solid/hollow distinction for attachments to cylindrical shells. WRC-297, on the other hand, is intended

only for cylindrical nozzles attached to cylindrical shells.

Boundary condition for using WRC 107:

To determine whether WRC 107 bulletin can be used for local stress checking the following geometry guidelines

must be met:

1. d/D<0.33 (Here, d=Nozzle diameter, D=Vessel outer diameter)

2. Dm/T=(D-T)/T>50 (Here, T=Vessel Thickness, Dm=mean diameter of vessel)

Boundary condition for using WRC 297:

To determine whether WRC 107 bulletin can be used for local stress checking the following geometry guidelines

must be met:

1. d/D<=0.5

2. d/t>=20 and d/t<=100 (Here t=nozzle thickness)

3. D/T>=20 and D/T<=2500

4. d/T>=5

5. Nozzle must be isolated (it may y 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:

The major differences other than the boundary conditions mentioned above are listed below:

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

stresses.

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.

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

Step by Step Methods for WRC 107 and WRC 297 Checking inCaesar II

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8/1/13 A Blog for Process Piping Engineering Professionals around the world: Step by Step Methods for WRC 107 and WRC 297 Checking in Caesar II

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attachments which can be rigid or hollow.

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

angle (Fig 3).

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

Limitations of WRC:

Other than boundary conditions mentioned above there are few more limitations as mentioned below:

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

2. CAESAR II and PVElite & CodeCalc will not extrapolate data from the charts when geometric limitations

mentioned above are exceeded. Extrapolated data may not be appropriate.

Inputs required for performing WRC checking:

The following documents must be ready with you before you start to perform WRC 107/297 checking:

1. Equipment Details/ General Arrangement drawing

2. Nozzle details

3. Line list

Step by Step methods for performing WRC 107/ WRC 297 calculation in Caesar II:

Step 1: Perform Static analysis of the stress system and find out the nozzle loads required for checking local

stresses.

Step 2: Enter into the WRC module from Caesar II. Provide a file name for your job

Step 3: Following screen will appear. Enter the Nozzle data as mentioned below:

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8/1/13 A Blog for Process Piping Engineering Professionals around the world: Step by Step Methods for WRC 107 and WRC 297 Checking in Caesar II

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Step 4: Now enter the vessel details i.e, diameter, wall thickness, corrosion allowance and material.

8/1/13 A Blog for Process Piping Engineering Professionals around the world: Step by Step Methods for WRC 107 and WRC 297 Checking in Caesar II

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Step 5: Input vessel and Nozzle direction cosines, Internal design pressure and load and moments values from

Caesar static analysis output (Sustained, Expansion and occasional as applicable).

Step 6: On options it is suggested not to change any parameter. Now click on analysis to read the results. The

output will inform you whether WRC checking is passing or failing. Use results as per your requirement.

8/1/13 A Blog for Process Piping Engineering Professionals around the world: Step by Step Methods for WRC 107 and WRC 297 Checking in Caesar II

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For entering loads and moments as per local convention following description and figure can be used for

converting global forces into local forces:

As shown in fig, Stretch your right hand with Middle finger along the Vessel Centerline. Index Finger should

parallel to nozzle centerline and should point in a direction from nozzle towards entering vessel. And Thumb

should be perpendicular to both. Then

1. Direction of Index Finger represents +P.

2. Direction of Middle Finger represents +VL

3. Direction of Thumb represents +VC

4. ML will be positive if by applying right hand thumb rule to ML, direction of thumb is same as that of VC.

5. MC will be positive if by applying right hand thumb rule to MC, direction of thumb is opposite to direction of

8/1/13 A Blog for Process Piping Engineering Professionals around the world: Step by Step Methods for WRC 107 and WRC 297 Checking in Caesar II

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VL.

6. MT will be positive if by applying right hand thumb rule to MT, direction of thumb is opposite to direction of P.

Get the loads and moments from CAESAR output. Compare the direction of Forces and Moments in CAESAR

output with conventional Force and Moment directions and enter the values of P, VL, VC, MT, MC and ML

accordingly.

Posted by Anup Kumar Dey at 10:14:00

Labels: Caesar II, code, piping stress, piping stress analysis, static analysis, tank, WRC

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