ASME III Subsections NC and ND - CAESAR II - Help

CAESAR II Users Guide

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CAESAR II
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CAESAR II Version
12

Calculate pressure stiffening using NC and ND

Pressure stiffening is not defined by default in this code. You can include pressure stiffening on bends in the analysis by including the Use Pressure Stiffening=Yes option in the setup file.

Flanged end modifications using NC and ND

Modifications resulting from flanged ends are permitted in this code providing the bend is not a widely spaced miter.

Minimum SIF for reinforced and unreinforced fabricated tees using NC and ND

The minimum SIF for reinforced and unreinforced fabricated tees is 2.1.

Calculate B1 and B2 using NC and ND

Calculate B1 and B2 according to the equations in ASME NC and ND.

Calculate liberal allowable using NC and ND

If you are using this piping code and define a dynamic load case as a “Expansion”, a request for Liberal Allowable is ignored and the (Sh-Sl) term is removed from the allowed limit (see below). This is a programming decision rather than an interpretation of the piping code or a recommendation for doing dynamic analysis.

Calculate stress intensification factors (SIFs) for intersections using NC and ND

Inplane and outplane SIFs for intersections are the same.

Using WRC 329 with NC or ND

For all intersections that are not welding tees or reinforced fabricated tees use the equation p*r2*t to calculate the approximate section modulus for the stress calculations.

This includes all reduced intersections and all d/D ratios.

Determine the branch SIF using NC or ND

If you do not want to use the branch SIF of the Code for welding and reinforced reducing tees, include the No Reduced SIF for RFT and WLT flag in the setup file.

Calculate the NC and ND stress allowables

Use the equations below to calculate the stress allowables.

Expansion Allowable = f(1.25Sc + 0.25Sh) + (Sh-Sl)

Sustained Allowable = 1.5Sh If not at an intersection

Occasional Allowable = 1.8Sh not greater than 1.5Sy, if OCC=1.2;

2.25Sh not greater than 1.8Sy, if OCC=1.5;

3.0Sh not greater than 2.0Sy, if OCC=2.0

Where:

f = Cyclic Reduction Factor

Sc = Cold Allowable

Sh = Hot Allowable

Sl = Sustained Stress from PD/4t+0.75iMb

Sy = Material Yield Stress

OCC = Occasional Factor from the CAESAR II configuration file

Calculate two pipe intersections using NC and ND

For two pipe intersections, for example butt welds or socket welds, B1 and B2 factors are 1.0. If the ratio of the average branch to average run radius is less than 0.5, then apply the reduced intersection rules to the B1 and B2 calculations regardless of the intersection type. If the reduced intersection rules do not apply then use the following rules for butt welded fittings:

B2b = 0.4 * (R/T)**2/3 but not < 1.0

B2r = 0.5 * (R/T)**2/3 but not < 1.0

You can modify the values for B1 and B2 for any node in the SIF&TEE auxiliary field. Any changes you make to B1 and B2 on an auxiliary field only apply for that element, regardless of whether the node is an intersection or not.

Calculate the ratio of r/R using NC and ND

When r/R < 0.5 use the following equations for B1 and B2:

B2b = 0.50 C2b but not < 1.0

B2r = 0.75 C2r but not < 1.0

C2b = 3(R/T)2/3 (r/R)1/2 (t/T)(r/rp), but not < 1.5

C2r = 1.15(r/t)1/4 but not < 1.5

Branch SIFs using NC and ND

WRC 329 produces smaller branch SIFs than ASME NC and ND, and the same run SIFs. The branch SIFs are smaller by a factor of 2. This is when d/D<0.5 and WRC 329 corrects the Mob (out of plane bending) inconsistency when d/D is between 0.5 and 1. In the lower ranges of d/D ratios WRC 329 is less conservative than the present codes and in the higher ranges WRC 329 is more conservative than the present codes.

Calculate Pvar using NC and ND

Pvar represents the difference between the operating pressure and Pmax, which is used in eq 11. CAESAR II forms occasional stresses by adding the sustained stress including pressure, and the occasional stress including the stress difference between the operating pressure and the peak pressure.

Limit for expansion stress range

To satisfy equations 10 or 11, the expansion stress, iMc/Z, must remain below the maximum of either f(1.25Sc + 0.25Sh) or f(1.25Sc + 0.25Sh) + (Sh-Sl) where Sl is the sustained stress as defined by equation 11: Sl= PDo/4tn+0.75iMa/Z.

Calculate moment summations using NC and ND

The approach taken by CAESAR II for moment summations at inter\-sections to satisfy equations 8 and 9 is to use the SRSS of the moments at each end of the pipe framing into the intersection. You do not have to adhere to the cumulative moment summation rules for a single intersection as per NB 3683.1. In addition, use the effective section modulus rules of NC and ND for all intersection stress calculations like equations 8 and 9. Use subsection NB to get the values for B1 and B2 only, and to compute the local flexibility if requested. Because of the use of this approach in CAESAR II, there is no allowable calculated for intersection points and sustained or occasional loads.

Determine sustained case SIF using NC and ND

Do not use the SIF in the ASME class 2 or 3 sustained stress calculations.

NC and ND reducer default values

The default flexibility factor value is 1.0. Use the following equation to determine the SIF value: 2.0 max or 0.5 + .01*alpha* SQRT(D2/t2).

Where:

D1- Diameter of the Large End

t1- Thickness of the Large End

D2 - Diameter of the Small End

t2 - Thickness of the Small End

Alpha - the reducer cone angle in degrees

Where:

Alpha = atan[ (D1-D2) / (2*length of the sloped portion of the reducer*0.6) ]

Alpha is the slope of the (concentric) reducer transition in degrees. If unspecified, CAESAR II calculates alpha using 60 percent of the entered reducer length. If left blank, the value is set from an estimated slope equal to the arc tangent times 1/2 the change in diameters times sixty percent of the entered reducer length.

Alpha cannot exceed 60º. The larger of D1/t1 and D2/t2 cannot exceed 100.

B1=.5 if alpha £ 30º, 1.0 if 30º < alpha £ 60º; B2 = 1.0.

There is an error in the code, the code states note 12 however, they meant note 14. Alpha cannot exceed 60º.