Stress Intensification Factors and Stress Indices Details - CAESAR II - Help

CAESAR II calculates SIFs automatically for bends and defined intersections as specified by the applicable piping code. You can type a user-defined SIF for any point in the piping system by activating the SIFs & Tees check box on the Classic Piping Input dialog box. Type the node number where the stress is to be intensified in the first available Node box. Type the in-plane and out-plane stress intensification factors in the In-Plane SIF (ii) and the Out-Plane SIF (io) boxes. Specify any axial and torsion index values on the elements on the Axial Index (Ia) and Torsion Index (It) boxes.

You cannot specify SIFs for bend elements unless the Allow User's SIF at Bend option is set to True in the configuration file. For more information, see Allow User's SIF at Bend. Code defined SIFs always apply.

CAESAR II does not allow user-defined stress intensification factors to be less than 1.0.

The node to be intensified must be the To or the From node on the current element.

Stresses are only intensified at the element end going to the specified node. For example, if two pipes frame into node 10, one going from 5 to 10, and the other from 10 to 15 and a stress intensification factor of 2.0 for node 10 is defined on the element from 5 to 10, then the 10 end of the element from 5 to 10 has a stress intensification of 2.0 and the 10 end of the element from 10 to 15 has a stress intensification of 1.0.

You can use user-defined stress intensification factors to override code calculated values for nodes at intersections. For example, let node 40 be an intersection defined by an unreinforced fabricated tee. The header pipes framing into the intersection go from 35 to 40 and from 40 to 45. The branch pipe framing into the intersection goes from 175 to 40. The code-calculated values for the stress intensification factors in the header pipes are:

SIF (ii) = 4.50

SIF (io) = 3.75

and in the branch pipe are

SIF (ii) = 6.70

SIF (io) = 5.58

Also assume that finite element analysis of the intersection showed the header stress intensification factors to be 2.3 and 1.87 respectively and the branch stress intensification factors to be equal to the code recommended value, which is 6.70 and 5.58. To properly override the code-calculated stress intensification factors for the header pipes, two pipe elements must be modified:

The stress intensification for the branch pipes can be calculated according to the code, so part of the branch pipe data might appear:

If either of the SIF boxes for the header elements going to 40 were left blank, the code-calculated value would be used in its place. This is only true where code-calculated values exist along with user-specified values.

If the element from 110 to 115 needs the stress intensification factors for each of its ends is 2.0, then a part of that element data might appear:

Leaving the out-of-plane stress intensification factor blank implies that it is equal to the in-plane stress intensification factor. There are no code-calculated values to override these user-input values.

If you do not specify Torsion SIF (it), Axial SIF (ia), and Pressure SIF (ip), CAESAR II calculates the values as 1.

The ASME B31.3 code update also introduced using the stress indices in sustained stress equations.

If you do not specify the In-Plane Index (Ii), then CAESAR II uses the greater value of either 0.75 multiplied by the In-Plane SIF value (ii) or 1.0.

If you do not specify the Out-Plane Index (Io), then CAESAR II uses the greater value of either of 0.75 multiplied by the Out-Plane SIF (io) or 1.

If you do not specify the Torsion Index (It), Axial Index (Ia), and Pressure Index (Ip), CAESAR II sets these values to 1.

Currently, the software does not use the Pressure SIF (ip) or Pressure Index (Ip) in the calculation.

You are not permitted to override code-calculated stress intensification factors for bend elements unless the Allow User's SIF at Bend option is set to True in the configuration file. Additionally, bend stress intensification factors supersede any code-calculated intersection stress intensification factors for the same node. This characteristic allows you to apply code-calculated intersection stress intensification factors to dummy legs without disturbing the normal bend stress intensification factors. The node on the dummy leg, which is also on the bend curvature, is defined as an intersection on the Intersection SIF Scratchpad. The intersection stress intensification factors are calculated and can be applied to the dummy leg end that connects to the bend. Bend stress intensification factors are unchanged.

Stress intensification factors can be calculated for intersections having one, two, or three pipes framing into it. Where two pipes form a partial intersection, CAESAR II assumes that the larger pipe is the header and the smaller the branch.

Where one pipe forms a partial intersection, CAESAR II assumes that the intersection is full sized.

CAESAR II does not calculate stress intensification factors for intersections having more than three pipes framing into it (for example, a cross, and for non-90-degree branches, such as lateral intersections).