Bottom Plate & Annular Ring Calculator

Minimum bottom plate requirements and annular bottom plate sizing (API 650 §5.4–5.5)

◉ API 650 §5.4–5.5 STYLE CHECK · NOT A REGULATORY SUBMISSION TOOL

⚠ Indicative tool only. Formulas and Table 5-1a/5-1b were checked directly against the standard's page images — the extracted text badly corrupted this table (misread every "≤" as "5"), so every value here was re-verified visually against the source. Applicable for effective product height H×G ≤ 23 m (75 ft); beyond that, an elastic analysis is required instead of this table.

Identification

Company

Tank ID

Location

Record Type

Research entries stay private to you for practice/testing. Switch to Official once this is a real design your company should see.

Units & Design Basis

Unit System

H — Maximum Design Liquid Level m

G — Design Specific Gravity

Bottom Plates (§5.4)

Corroded Bottom Plate Thickness mm

Rectangular / sketch plate

Plate Width mm

Projection Beyond Shell mm

Bottom is sloped toward center

Checks

Minimum corroded thickness (6mm / 0.236in)—

Minimum width if rectangular/sketch (1800mm / 72in)—

Minimum projection (50mm / 2in)—

Minimum slope (1:120) if sloped—

Butt-Weld vs Lap-Weld Determination (§5.5.1)

Bottom Shell Course Material Group

Determination Not evaluated

Annular plate weld requirement—

Annular Plate Radial Width (§5.5.2)

t_b — Annular Plate Thickness (proposed) mm

Result

Absolute minimum (§5.5.2 base)—

Calculated minimum (215t_b/√(HG) or 390t_b/√(HG))—

Required radial width (governing)—

Annular Plate Thickness — Table 5-1a/5-1b (§5.5.3)

The stress values below are what the table actually needs — the maximum stress in the first shell course, which the standard defines from the Shell Design results: Product Stress = (t_d−CA)/(corroded t)×S_d; Hydrostatic Test Stress = (t_t/nominal t)×S_t. Enter these from your Shell Design calculation, or the plain allowable stresses S_d/S_t if you haven't computed the actual stress.

First Course Plate Thickness (Product) mm, corroded

Product Stress in First Course MPa

First Course Plate Thickness (Hydrotest) mm, nominal

Hydrotest Stress in First Course MPa

Result Not evaluated

Table 5-1 thickness — product condition—

Table 5-1 thickness — hydrotest condition—

Required annular thickness (governing)—

Your proposed t_b vs required—

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