is it possible to override specific pipe section properties ( such as moment of inertia, section modulus) in the pipe input of CAESAR II

No - pipe section properties are computed based on the diameter and wall thickness of the cross section. There is no "override" for these values in the piping module.

Depending on what you are doing, you can specify a user defined cross section in the Structural Modeler. You can then analyze this as a stand-alone model, or include it in a piping model.

Individual pipe ELEMENT properties can be modified by several techniques, i.e Rigid, expansion joint, or user defined material for an element. It depends on what is attempted to be modeled without changing parameters that are used for weight calculations. If a corrugated or ribbed wall is being modeled, then it might be possible. Sections that are not circular - like oval, rectangular , square - would have more error in trying to model based on diameter & wall. What is it that you are trying to represent or to model ?

I am trying to model a pipe with mechanical split sleeve reinforcement. This reinforcement should be considered for bending stress and not for hoop stress calculations. So I want to override section modulus/moment of inertia without changing the diameter/thickness.

As previously stated, there is no facility to directly override the cross section properties of the pipe element. You can however make the following adjustments, but there are side-effects.

<font color="#0000ff">Modulus of Elasticity</font>
You can alter this value, which is used in the formulation of the stiffness matrix. However, this will alter all terms, not just the bending term.

<font color="#0000ff">Rigid Designation</font>
If you call a pipe element rigid, then CAESAR II will compute the cross section properties assuming the wall thickness is "ten times your specified value". This will also affect all terms in the stiffness matrix as both "A" and "I" will be affected. Another issue here is that CAESAR II doesn't compute stresses on rigid elements, because in general you don't know the cross section.

<font color="#0000ff">Expansion Joint</font>
Designating the element as an expansion joint allows you to set the major stiffnesses. However, CAESAR II doesn't compute stresses on expansion joint elements.

<font color="#0000ff">Structural Element</font>
If you use the Structural Modeler, you can setup a User Defined Cross Section where you directly specify the area and inertia of the section. This is the most exact way to get what you want. As with the rigid and expansion joint elements, CAESAR II doesn't compute stresses on structural elements.


I still feel the structural element is your best course of action.

Sitaram,
I think that you are trying to model something similar to the reinforcement of a corroded wall section of pipe. You seem to have more concerns for bending and loads, so you want to do a more precise analysis. I would suggest modeling the mechanical sleeve as another pipe element, but with ZERO internal pressure. This would be like modeling a section of jacketed pipe, where your pressure containment is in the gut pipe, and the mechanical sleeve is the jacket pipe element. The gut pipe elememt and the jacket pipe element should have same end nodes, so overall bending properties would be composite of the two sections. After inserting and defining the jacket pipe element for the mechanical sleeve, remember to reset the continuing pipe parameters for pressure, diameter, wall thickness, etc.
I would have to think about the hoop stress in the pipe. The mechanical sleeve might not be leak tight, but if the sleeve limits any "ballooning" of the pipe diameter, then the hoop stress is also partially sustained by the sleeve. The sleeve design probably should indicate how the sleeve adds reinforcement to hoop and bending directions. If the sleeve ends are not welded or firmly gripping the pipe, then the bending stiffness contribution would be smaller.

A question on the answer from Richard above:
What about Young's Modulus for the rigid element?
I think it remains the same as pipe material? Am I right?

From the help file:

Rigid
(Units: lb.)

Indicates that you are supplying rigid element data. Select or clear this option by double-clicking the Rigid check box on the Classic Piping Input dialog box.

Type a value for Rigid Weight. This value should always be zero or positive and should not include the weight of any insulation or fluid. If you type no weight, then CAESAR II models the element as a weightless construction element.

Rigid weights are defined automatically if you use the Valve and Flange database.

CAESAR II automatically includes 1.0 times the fluid weight of equivalent straight pipe and 1.75 times the insulation weight of equivalent straight pipe.

Rigid elements with zero weight are considered to be modeling constructs and do not have fluid or insulation weight added.

The rigid element stiffness is proportional to the matching pipe. For example, a 13 in. long 12 in. diameter rigid element is stiffer than a 13 in. long 2 in. diameter rigid element. This fact should be observed when modeling rigid elements that are part of a small pipe/large vessel, or small pipe/heavy equipment model. The stiffness properties are computed using 10 times the thickness of the rigid element. For additional details, see Technical Discussions.

If you want, you can specify a different value for "E" on the rigid element, just make sure to set it back to the appropriate value for the pipe material on the next element.