Yield-strength and modulus reduction, modified allowable stress, roof / wind-girder / cleanout adjustments, and the shell-to-bottom cyclic evaluation for tanks above 93 °C (200 °F) up to 260 °C (500 °F)
◉ API 650 11TH ED. WITH ADDENDA THROUGH ADDENDUM 3 · EFFECTIVE 1 FEB 2012 · APPENDIX M · NOT A REGULATORY SUBMISSION TOOL
⚠ Indicative tool only. Source: Appendix M as supplied (revision bars 07, 08, 09 and 11 — the 11th Edition through Addendum 3). Every value was read from the page images. Table M-1 (yield-strength reduction factors) and Table M-2 (modulus of elasticity) were checked against their USC counterparts: the factors are identical, and the USC moduli convert to the SI moduli within 0.2%. The two M.4.2 stress formulas (SI and USC) were checked against each other by converting a worked case both ways; they agree to about 1–2%, consistent with rounding of the printed constants.
Read this before relying on it. (1) M.4.2 is stated in the standard to be a recommended design practice, not a mandatory one. (2) Exclusion condition (a) prints its temperature limit as “220 °C (400 °F)”, which are not equivalent (400 °F is about 204 °C); the tool applies the value printed for the unit system you select. (3) The expression in exclusion condition (b) is smudged in the supplied scan; I read it as 0.3(D·t)0.5 with D in feet, t in inches and the head in feet, which matches the (D·t) grouping used throughout the S formula and works out to roughly 1.5×√(R·t), about the shell's bending length scale, which supports the reading — but confirm it against a clean copy. (4) The tool multiplies or reduces values that you take from parts of API 650 not supplied (Table 5-2 product design stress, the 5.9.7.1 wind-girder height, the 5.10.5/5.10.6 roof thickness, 5.10.3 structural stresses), so those inputs are yours to enter. (5) The temperature tables begin at 94 °C (201 °F); between 93 and 94 °C the first row is used.
Identification
Research entries stay private to you for practice/testing. Switch to Official once this is a real design your company should see.
Uses t = 4.9·D·(H−0.3)·G / Sd + CA (SI) or 2.6·D·(H−1)·G / Sd + CA (USC), the formula in the Shell Design tool, which reproduced all ten courses of the HPCL calculation. Appendix M changes only the design (product) stress; it does not mention the hydrostatic-test stress, so the test thickness is not adjusted. Requires the Table 5-2 product design stress above. The one-foot method applies up to 60 m (200 ft) diameter.
Shell-to-Bottom Junction — Cyclic Evaluation (M.4.2) Not evaluated
T = maximum design temperature − minimum ambient. Sy is the bottom plate's yield at the maximum design temperature (the Table M-1 reduction is applied for you). The formula assumes the shell is at least as thick as the annular plate (t ≥ tb). The formula gives a fatigue-type curve: I read N as the number of cycles the junction can sustain at stress S — the clause words it as the design-life cycle count, but the relationship N = (9.7×10³/KS)2.44 is a stress-versus-cycles curve — and compare it with your estimate.
Check
Result
Other Appendix M Provisions
Nameplate (M.1.6): add “M” to the information required by 10.1.1 and mark the maximum design temperature in the space shown in Figure 10-1.
Bottoms (M.4.1): tanks over 30 m (100 ft) diameter shall have butt-welded annular bottom plates (5.1.5.6).
Thermal effects (M.2): the appendix gives no detailed rules; the Purchaser is to define significant thermal effects. Consider (a) temperature differences between the bottom and the lower shell — possibly needing more piping flexibility, an improved bottom-to-shell joint and a thicker annular ring or sketch plates; (b) the bottom's ability to expand thermally; (c) gradients between members such as shell and roof, stairways or stiffeners and at insulation discontinuities; (d) whether contents may solidify and be reheated, including effects on columns, beams and rafters and the risk of plugging vents; (e) the number and magnitude of temperature cycles.
Other multipliers (M.3): the structural allowable stresses of 5.10.3 (including those dependent on modulus of elasticity) and the yield strength Fy in 5.10.4.4 are multiplied by the reduction factor (M.3.3, M.3.6). For Appendix A tanks the 145 MPa (21,000 psi) allowable in A.4.1 is multiplied by the reduction factor (M.3.4). If anchors are insulated, the Table 5-21 and 5-22 allowable stresses are multiplied by (yield at temperature ÷ 205 MPa) when that ratio is below 1.0 (M.3.9).