What is WRC?
WRC or Welding Research Council is a Scientific Research Corporation, involved in solving problems related to welding and pressure vessel technology. To date, they have published more than 500 bulletins which solves various problems of engineering.
Importance of WRC 107 (537) and WRC 297 in Piping Stress Analysis
Whenever Pressure Vessel or Heat exchanger (Static Equipment) nozzle loads exceed the allowable values provided by Vendors (Equipment manufacturer) or standard project-specific tables (guidelines), the piping stress professional is permitted to use WRC 107 (537)/297 (or any other FEA) to calculate the stresses at the Nozzle-Shell junction point and compare the calculated 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 that must be satisfied before using WRC. This small write up will try to explain the required details for performing WRC 107 (537) and WRC 297 using Caesar II and step by step method for performing WRC check.
What is WRC 107 (537) and WRC 297?
Both WRC 107 (537) and WRC 297 bulletins deal with “local” stress states in the vicinity of an attachment to a vessel or pipe. As indicated by their bulletin 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 a un-penetrated shell, while WRC-297 assumes a circular opening in a 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 conditions for using WRC 107/ WRC 537
To determine whether the WRC 107/ WRC 537 bulletin can be used for local stress checking the following geometry guidelines must be met:
- Dm/T=(D-T)/T>50 (Here, T=Vessel Thickness, Dm=mean diameter of vessel)
Boundary conditions for using WRC 297
To determine whether WRC 297 bulletin can be used for local stress checking the following geometry guidelines must be met:
- d/t>=20 and d/t<=100 (Here t=nozzle thickness)
- D/T>=20 and D/T<=2500
- The nozzle must be isolated (it may not be close to a discontinuity) – not within 2√(DT) on the vessel and not within 2√(dt) on the 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 that can be rigid or hollow.
4. WRC 297 is not applicable for nozzles protruding inside the vessel (Fig 1), Tangential Nozzle (Fig 2), Nozzle at an angle (Fig 3).
5. Typically, WRC-107 is used for local stress calculations and WRC-297 is used for flexibility calculations.
Limitations of WRC 107 & WRC 297
Other than boundary conditions mentioned above there are few more limitations as mentioned below:
- Neither bulletin considers shell reinforcement nor do they address stress due to pressure.
- CAESAR II, PVElite & CodeCalc will not extrapolate data from the charts when the geometric limitations mentioned above are exceeded. Extrapolated data may not be appropriate.
WRC-107/ WRC-297 calculation Methodology in Caesar II
Inputs required for performing WRC checking
The following documents must be ready with you before you start to perform WRC 107/297 checking:
- Equipment Details/ General Arrangement Drawing
- Nozzle details
- Line list
WRC Calculation Steps in Caesar II
Step 1: Perform Static analysis of the stress system and find out the nozzle loads required for checking local stresses.
Step 3: The following screen will appear. Enter the Nozzle data as shown in Fig. 3 below.
Step 4: Now enter the vessel details i.e, diameter, wall thickness, corrosion allowance, and material (Fig. 4)
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 requirements.
For entering loads and moments as per local convention following description and figure (Fig. 7) can be used for converting global forces into local forces.
As shown in Fig. 7, Stretch your right hand with the Middle finger along the Vessel Centerline. Index Finger should parallel to nozzle centerline and should point in a direction from nozzle towards entering the vessel. And Thumb should be perpendicular to both. Then
- The direction of the Index Finger represents +P.
- The direction of Middle Finger represents +VL
- The direction of Thumb represents +VC
- ML will be positive if by applying right-hand thumb rule to ML, the direction of thumb is the same as that of VC.
- MC will be positive if by applying right-hand thumb rule to MC, the direction of thumb is opposite to the direction of VL.
- MT will be positive if by applying right-hand thumb rule to MT, the direction of thumb is opposite to the 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.
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