Dear Sir,

While carrying out the design calculations for Backing ring thicknesses, using PV Elite, we have observed the following:

PV Elite is considering formula (T = SQRT (WM1 * h * Split_fac * Y / S * B)) as given for style B split factor for calculating backing ring thicknesses as TEMA (RCB-5.141) style A does not cover any split factors in calculations as the formula (T = SQRT ( W * h * Y / S * B)) as split factor 2 as used for style B is missing .

ASME appendix 2 clause 2.9 indicates philosophy of split factor for splits. Factor is 2 with one split (2 segments) and 0.75 when the backing ring is split into 4 segments. Formula as given in appendix 2.7 of clause B is similar to as given in TEMA which is referred in clause 2.9.

In PvElite help files, for user input of split factors for backing ring design, it indicates that “Note - TEMA RCB-5.141 shows different styles of backing devices. Styles A and D have a split ring, but the moment used to design them is not increased. When you have one of these styles, enter zero as the number of splits to get the same effect in CodeCalc”.

We would like to know why there is no split factor for style A, C and D. We have not seen any provision for split A, C and D type backing ring in ASME.

Hello Anup,

The basic formula for backing ring thickness per the TEMA equation is generic as you noted. In PV Elite or CodeCalc when the number of splits is entered in, the value of Split_fac is determined and inserted into the equation. Note that there is not a distinction in the input for the style of backing ring per TEMA.

If you change the number of splits, analyze and compare the results, you should definitely notice a difference in the results. It is important to note that the required thickness is the thickness of each element or piece of the backing ring. So for a ring with 2 splits the overall thickness would be twice the required thickness as reported by the software.

Hopefully this helps you.

Thanks Scott,

based on your reply we presumed that Coade is following ASME formulae for calculating backing ring thickness (T) for bending same as per TEMA RCB-5.141.




As per appendix 2-9 clause a) & b) and the formulae given in appendix 2-7, we understand that following Mo shall be considered:

Loose flange (Solid):Split factor will be 0 (Moment = 100%, Split_fac = 1)
Single split : Split factor will be 1 (Moment = 200%, Split_fac = 2)
Double split : Split factor will be 2 (Moment = 75%, Split_fac = 0.75)

If our above understanding is correct then the note given in PV Elite help file (refer below) is violating the proper selection of number of split factor for design of backing ring thickness.

“Note - TEMA RCB-5.141 shows different styles of backing devices. Styles A and D have a split ring, but the moment used to design them is not increased. When you have one of these styles, enter zero as the number of splits to get the same effect in CodeCalc”.

Please clarify.

Hello Anup,

The best way of seeing how PV Elite performs the analysis is to study the output by trying a different number of splits. If you study the results line by line, you can see what PV Elite does. That is the best way of getting this question anwered.

Mr. Ray,

Thanks for your reply.

I have done this exercise by applying different number of splits and that is okay as per code.

My worry about the help note indicated in PV Elite help file (for selection of split factor) which is deviating the code.

Expecting reply from Intergraph and members

Someone will look at the help for the 'Number of Splits' and insure it is correct.