T IPS: W R C - 1 0 7 A NALYSIS

Information:What is the WRC-107 Analysis? The WRC-107 Analysis calculates the combined local stressintensity from external loads at the junction of an attachment and a shell or head. The method may beemployed for structural supports or nozzles.What are the limitations? The analysis is based on empirical data. Certain geometries falling outsidethis data have no experimental basis to support them and it is up to the designer to determine if themethod is a valid approximation outside the range covered by the empirical data. In addition, the methoddoes not cover stress from internal pressure; however, DesignCalcs does allow for internal pressureloading. (View How To: Understand the Pressure Stress Calculations in the DesignCalcs WRC-107 Implementation)The second major limitation is the stress combination. This method combines the membrane andbending stresses. Membrane only stress will have a set of allowable stress criteria if you look to SectionVIII, Division II, and the combined membrane and bending stress will have its own allowable stresscriteria. In addition, if you need to consider peak stress, the failure modes you need to check per DivisionII get more complicated.Finally, the WRC-107 reference does not clearly indicate the attachment details for the attachment to thehost. When utilizing this method, be careful when considering tilted or hillside nozzles or attachmentswhere full penetration groove welds are not used.How does the WRC-107 coordinate system work? See the figures below for reference. For bothheads and cylinders as hosts, the radial load P is positive if it is inward. Choose arbitrary 1-1 and 2-2axes that are normal to each other for heads. A shear load V2 acts in the 1-1 direction and causes the M1moment. A shear load V1 acts in the 2-2 direction and causes the M2 moment.For cylindrical hosts, the axes are the longitudinal direction and the circumferential direction. A positiveshear load VC acts in the positive circumferential direction and creates the positive moment MC. Thepositive shear load VL acts in the positive longitudinal direction and creates the positive moment ML.

How does the Solve For radio button work? When stresses are selected, the analysis will calculatethe combined local stress intensity from all of the loads entered. When one of the other options isselected, the analysis will set the combined stress to its maximum and solve for the item selected withthe other items set.What should I enter for the stress multipliers? - These multipliers are used to determine the allowablecombined stress. Cs represents the stress multiplier and Cy represents the yield multiplier. You maychoose which combination of stress, yield, and multiplier to use and whether to consider the attachmentproperties. When the attachment properties are considered, the minimum of the selected yield, the stressof the host, or the stress of the attachment is used to determine the allowable stress.The ideal values for the stress multipliers depend on several factors, including the duration andgeography of the load. If the load is to be applied one time and then released (such as for lifting lugs), ahigher allowable may be justified. A typical operating nozzle load would be limited to a lower allowable.See the stress classifications in Section VIII-II for further guidance. Pay special attention to the primarylocal and secondary stresses and the slight differences between them.An example of a typical allowable stress for primary local membrane stress would be 1.5*S. An exampleof a typical allowable stress for primary local membrane plus secondary bending stress would be Spswhere Sps may be either 3*S or 2*Sy. Be careful when specifying 3*S if the allowable stress criteria isbased on 90% yield instead of 66-2/3% yield.When do I use the Stress Concentration Factor? This is only used for cyclic type loadings or forbrittle materials. See appendix B in WRC-107 and proceed with caution.How does the analysis handle reinforcing pads for nozzles? The analysis will calculate thestresses at the periphery of the nozzle to host/pad combined thickness and it will calculate the stressesat the periphery of the pad diameter to host junction. This is probably a conservative leaning check unlessthe repad thickness is very close to external projection of the nozzle or the width of the pad is verynarrow; in either of those cases, the check is more accurate.

For a large diameter pad (e.g. a pad with 2x the diameter of the nozzle neck), it may be suitable toincrease the host thickness to represent the combined thickness of the pad and the host - assuming theallowable stress of both are the same and the nozzle has a quality attachment detail to both the pad andthe host wall.Can I bump up the host thickness to represent the combined host and pad thickness for astructural attachment Yes, you can. However, this approximation is the most viable when theattachment is attached through the pad to the host wall and the details include full penetration groovewelds. In addition, the pad should be fairly large compared to the attachment size (e.g. 8 x 8 pad for a4x 4 attachment) and the pad should have an allowable stress similar to the host.How can I import a nozzle or a host that I have already designed? On the Vessel/Attachment tab,select the Nozzle Browser to import the information for the nozzle and its host. To add a structuralattachment, select the host browser and bring the host information into the WRC-107 form. Then you canmanually enter the attachment information.Why do I need to enter the diameter when the host is an elliptical head? The analysis treats thehead as a sphere and uses the diameter entered to determine the spherical radius.Are the wind loads, elevations, and diameters from the Vessel Information andAttachments/Loadings windows used in the WRC-107 Analysis? - In order for wind loads to beconsidered in the WRC-107 Analysis, they must be directly entered on the Loads tab of the WRC-107window. The analysis does not draw this data from any other location.

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H OW T O: U NDERSTAND THE P RESSURE S TRESS C ALCULATIONS IN THED ESIGNC ALCS W R C - 1 0 7 I MPLEMENTATION

Query:What is the basis for the Pressure Stress Calculations in the WRC-107 check as utilized in DesignCalcs?

Response:

GeneralThe WRC-107 method only considers external loads and does not consider pressure.The pressure stress equations used in the DesignCalcs implementation of the WRC-107method are for primary membrane stress caused from internal pressure.The stresses caused by the external loads are typically classified as primary local stressand secondary bending stress (although this is not always the case).If pressure is considered for these calculations, the primary membrane stress from pressurewill be added stresses determined from the external loads.

Pressure Stress Calculation: Elliptical HostThe pressure stress for an elliptical host in the WRC-107 method assumes that the host can act like asphere at the location where the attachment/nozzle is placed. The diameter entered must represent aneffective spherical diameter at this location. The formula is derived from the UG-27(d) formula fromASME SC VIII-I (setting E=1).

Elliptical Host Pressure Stress vs. Elliptical Head Actual StressThe Actual Stress formula for an elliptical head is derived from ASME SC VIII-I Appendix 1-4(c).

As you can see, these equations are not the same and thus will produce different results.In addition, the elliptical head form has a location to enter thin out; the WRC-107 form lacks this field, so ifthe math needs to consider local thinning at the attachment/nozzle, the thickness must be reducedmanually to reflect that. The Actual Stress in the elliptical head report also considers adjustment for thejoint efficiency as joint efficiency is typically applied as a penalty to the allowable primary stress.

Tips: WRC-107 AnalysisInformation: