#load Cases for stress Analysis

 #load Cases for stress Analysis

Mainly only three cases are include in basic code stress analysis-

                                                                                        1.Design Pressure

                                                                                        2.Oprational weight

                                                                                        3.Maximum Thermal Expansion

In thermal expansion , it is customary to only calculate , the condition where all piping segments involved are at their maximum and minimum temperature.  

Different operating modes with various temperature  combination are not investigated.

The extra analysis is only performed when required by design Specifications.

For earthquake analysis(4), normally the static equivalent approach is used.

. In this approach, horizontal forces proportional to the weight are applied. The weight shall include all the operation weight such as pipe, insulation, fluid content, refractory, etc.

the proportional constant is referred to as the g factor, which is defined in the design specification based on seismic zone classification. 

Unless specified otherwise, only two directions of horizontal forces are analyzed. The vertical force, which can be significant, is not analyzed. This is somewhat justified because the piping has to be supported vertically for its weight in the first place.

 Past experience has also indicated that an earthquake can shake in all three directions randomly at the same time. Therefore, each direction of the force is analyzed independently, and the results are combined by the square root of the sum of squares (SRSS) method to arrive at the combined seismic effect. Different combination methods can be specified to satisfy special situations.

For wind analysis(5) , static forces proportional to the piping projection area are applied.

Piping systems identified as vibration(6) lines are normally checked for their natural frequencies to prevent structural resonance by vibratory frequencies. 

The supports are designed with special attention to rigidity and damping effects. However, vibration analysis is not performed due to the lack of definite forcing functions. It is performed only for troubleshooting after the piping experiences noticeable vibration.

Although analyses on some steam/water hammer effects(7), such as steam turbine trip and open discharge safety valve opening, have become more common, they are still not usually performed unless explicitly specified.