2007 Edition: Allowable Stresses

[TomBarsh]

Here is something that I'm sure will catch a lot of people unaware.

The 2007 Edition ASME Code, Section II Part D provides new rules for determining the allowable stress at intermediate temperatures (those not listed in the stress tables). The rules effectively limit the number of significant digits that can be used when deriving the allowable stress for intermediate temperatures. See General Notes (b) to Table 1A (similar notes apply to the other stress tables).

For example, consider SA-516 Gr 60, listed on page 10, line 30 operating at 550° F.

S @ 500° F = 17.1 ksi
S @ 600° F = 16.4 ksi

Interpolating for 550° F:

S (ksi) = (y2 - y1) / (x2 - x1) * (x - x1) + y1
= (16.4 - 17.1) / (600 - 500) * (550 - 500) + 17.1
= 16.75

But Note "(b)" to Table 1A, Section II Part D, specifies to round to the number of decimal places given in the Table for the stress value at the higher temperature, which is one decimal place. Thus we get 16.8 ksi or 16,800 psi.

COMPRESS follows these new rules for the 2007 Edition but retains the previous method (allowing the number of significant digits to float) for earlier Editions/Addenda.

Tom Barsh
Codeware Technical Support