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 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 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, 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:

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

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.

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. Then1.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 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.

PIPELINE METALLURGICAL
FAILURE ANALYSIS

"Determine the optimal span between pipe supports for thin walled piping systems" International Conference on researches in Science and Engineering
28 July 2016, Istanbul University, Turkey