Prior to the recent B31.1 edition, the expansion coefficients were almost the same between B31.1 and B31.3. The new B31.1 changed these coefficients. The table below shows the values for "low carbon" steels.
<table border="1" cellpadding="10" bordercolor="#0000ff"><tr><th>Temp (°F)</th> <th>New B31.1</th> <th>Old B31.1</th><th>B31.3</th></tr><tr><td>-325</td> <td>5.5</td> <td>5.0</td> <td>5.0</td></tr><tr><td>-150</td> <td>5.9</td> <td>5.5</td> <td>5.5</td></tr><tr><td>-50</td> <td>6.2</td> <td>5.8</td> <td>5.8</td></tr><tr><td>70</td> <td>6.4</td> <td>6.07</td> <td>6.07</td></tr><tr><td>200</td> <td>6.7</td> <td>6.38</td> <td>6.38</td></tr><tr><td>300</td> <td>6.9</td> <td>6.60</td> <td>6.60</td></tr><tr><td>400</td> <td>7.1</td> <td>6.82</td> <td>6.82</td></tr><tr><td>500</td> <td>7.3</td> <td>7.02</td> <td>7.02</td></tr><tr><td>600</td> <td>7.4</td> <td>7.23</td> <td>7.23</td></tr><tr><td>700</td> <td>7.6</td> <td>7.44</td> <td>7.44</td></tr><tr><td>800</td> <td>7.8</td> <td>7.65</td> <td>7.65</td></tr><tr><td>900</td> <td>7.9</td> <td>7.84</td> <td>7.84</td></tr><tr><td>1000</td> <td>8.1</td> <td>7.97</td> <td>7.97</td></tr><tr><td>1100</td> <td>8.2</td> <td>8.12</td> <td>8.12</td></tr><tr><td>1200</td> <td>8.3</td> <td>8.19</td> <td>8.19</td></tr><tr><td>1300</td> <td>8.4</td> <td>8.28</td> <td>8.28</td></tr><tr><td>1400</td> <td>8.4</td> <td>8.36</td> <td>8.36</td></tr></table>
I don't want to say the codes are diverging, its just that with this edition, B31.1 made a change. We'll have to wait and see what the next B31.3 does.
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