Hello, there: I am trying to follow the CAESAR II V5.10 Applications Guide for Vertica Dummy Leg on Bends, but I got a problem: I figured out the example in “Offset Element Method” is using NPS 10” pipe (Actual OD=10.75”, R=1.5*10=15”). Based on “Vertical Leg Attachment Angle”: AB=Nominal R + ½ Act. OD=15+10.75/2=20.375; Cos(a)=R/AB=15/20.375=0.7362 So, Alpha= 42.59 X=R(1-Cos(a))=3.96” Y=3.64” But the example in “Offset Element Method”: X=-4.39”, Y=4.39 Please help where I did wrong and which method is the most popular used acceptable method for model vertical dummy leg on bend? Thanks in advance

IMHO it is not normally necessary to go to these lengths modelling a dummy leg. You have a whole lot of approximations in your calculation already, since wall thickness and thus weight and stiffness throughout may vary by +/-12.5% dependent upon material and code. In addition, every restraint has flexibility which we nearly always omit.

Since attaching a dummy leg will probably destroy any flexibility in an elbow, ignore the elbow. Model a direction change and to be conservative, apply the correct sifs to both the attached elements. Either attach the dummy leg and support ,or simply support the intersection point. That depends on temperature mostly.

Complex modelling is certainly justified sometimes, but by no means always.

If it is high tenp line then scrap the dummy leg idea.

I always model the dummy from node M at the bend. The first 100mm of the dummy pipe directly connected to the header is to be modeled with the header temperature (for correct allowable stress). The rest of the dummy pipe is to be modeled with the average temperature between ambient and calculation temperature of subject spool piece. Including the correct SIF...

I agree with MoverZ. I do not model vertical dummy legs unless there is stop or guide on it with huge loads and dummy leg length is more. However I do model the horizonal dummy legs.

If modeliing verical dummy legs at all points is required, why do not model all the shoe with average temperature? Even shoe is atleast 6" high similar to many dummy legs? Why not place all support from the bottom of pipe with rigid elements instead of centre which we do usually to take care of radial expansion?