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2.2.10.3 Specifying Design Code Data

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1) Choose Input>ASME Sec VIII Div 3 Input or click ASME Sec VIII Div 3 Input button .  The ASME Sec VIII Div 3 Data Input dialog box appears.  Note that for the stress type entered, only smooth bar fatigue curve is activated.  The welded joint fatigue curve is deactivated; the weld fatigue analysis is available only when membrane stresses, bending stresses, or shear stresses are entered.

 

 

2) In the Spec No. drop-down menu, choose SA-516.  The Material Selection dialog window pops up to refine the selection.

 

 

Choose SA-516 70 and click Confirm Selection button.  When the following dialog box pops up, click Confirm highlighted material button, then the next window will display allowable stresses at temperatures.  This step is neccessary because for the same material, there are two different sets of allowable stresses, one set for short term, and one set for long term considering creep effect.  If not sure which set is appropriate, consult ASME code book.  But for this material, there is only one set.  Click Start over button to try again, or click OK button to confirm.

 

With the selected material, the program automatically suggest a fatigue curve.

 

 

The fatigue curve for the selected material can be plotted by clicking Plot button.  You can zoom, print or export the chart, or change the styles of the chart by clicking the buttons on the tool bar.  Click X button on the upper-right corner to close the window.

 

 

If you are not satisfied with the suggested fatigue curve, click Change button to choose a different curve in the following pop-window.

 

 

Click OK button to confirm the selection or Cancel button to discard.

 

3) Leave 1.0 in the Sn:Sp ratio box unchanged.

 

Sn = primary + secondary stress (Pm + PL + Pb + Q)

 

Sp = primary + secondary + peak stress (Pm + PL + Pb + Q + F)

 

It is required that entered stresses be Sp so that Sn is derived from Sp by Sn:Sp ratio (<= 1.0). Leaving Sn:Sp ratio = 1.0 is conservative.

 

4) Click Smooth bar correction factors button.  The ASME Sec VIII Div 3 Data Input dialog window displays.

 

 

In the Fatigue strength reduction factor group box, choose Kf = 1.0.

 

The Roughness factor group box is for roughness factor calculation.  The roughness factor Kr is calculated according to the value of either average surface roughness Ra or maximum surface roughness Rmax.  Note that the following fatigue curves have specific surface roughness applicabilities:

 

Figure KD-320.1 and Figure KD-320.4, applicable for an average surface roughness of 19Ra μin. (0.5Ra μm) or a maximum surface roughness of 59Rmax μin (1.5Rmax μm).

 

Figure KD-320.2 and Figure KD-320.3, the influence of the surface roughness is included in the curve, i.e., Kr = 1.0; therefore, a surface roughness factor need not be applied. In these cases, enter Ra = 1 μin. (enter Ra = 0.11 μm. in metric unit system), or enter Rmax = 1 μin. (enter Rmax = 0.1 μm. in metric unit system).

 

Recall that the fatigue curve KD-320.2 was selected, therefore enter 1 (μin.) under Average surface roughness Ra radio button.

 

The vessel mean stress type group box is for mean stress considerations.  Autofrettage is one of several processes that can be used to produce favorable residual stresses in thick‐walled pressure vessels. The theory of autofrettage is based on the fact that the stress in a thick‐walled cylindrical vessel is higher at the bore than at the outside surface for a given internal pressure. If such a vessel is subjected to a continuously increasing pressure, the entire vessel will deform elastically until some pressure is reached at which the material at the bore begins to plastically deform. As the pressure continues to increase, the boundary at which material begins to yield moves from the bore through the vessel wall until it reaches the outer wall, causing plastic collapse [see KD-210(e)(6)]. In the process of autofrettage, the pressure is increased from the point of first yielding at the bore to a pressure that will place the elastic–plastic interface at the desired radius. The removal of this pressure then produces compressive residual tangential stress at the bore and tensile residual tangential stress at the outer wall.

 

Because autofrettage is not specified in fabrication requirement, choose NonAutofrettaged with tensile mean stress radio button.

 

Now the data input is complete.  Notice that in the information window, the calculated roughness factor Kr = 1.000.

 

 

Click OK to return to home window.

 

 

 

 

 

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