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API 653 & 570 Storage Tank & Piping Integrity Assessment

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Module 1 of 4 14 min read

API 650/653 Storage Tank Mechanical Layout

💬 In Plain Terms: How giant storage tanks are built: shell rings, bottom plates, and roofs
Everyday Analogy (How to Picture This)

Imagine a tin can the size of a football stadium holding 10 million gallons of crude oil. The tank walls are made of steel plates rolled into rings and stacked on top of each other. Because liquid pressure is greatest at the bottom, the bottom ring is thick solid steel (up to 1.5 inches), while the top ring is thin (0.25 inches). In this module, you learn the mechanical architecture of storage tanks.

Engineering Principles & Technical Theory

1. Atmospheric Tank Anatomy (API 650/653)

Shell Courses: Numbered from bottom (Course 1) to top. Course 1 withstands maximum hydrostatic pressure head.

Bottom Plates: Annular plates (heavy outer ring directly supporting the shell) and Sketch plates (interior floor plates lap-welded together).

Roof Types: Fixed Cone Roofs, Dome Roofs, and Floating Roofs (Internal/External pontoons that float directly on liquid to eliminate explosive vapor space).

Step-by-Step Practical Field Procedure

1

Visual Inspection of Annular Ring Chime

Ref: API 653 Section 6.3

Inspect the external bottom projection (chime) extending outside the tank shell for soil moisture corrosion and settlement cracks.

Target Defect Identification & Morphology

Annular Plate Fatigue Cracking

Critical / Reject

💬 Cracks at the 90° corner weld where the vertical tank wall joins the bottom plate.

Instrument Signature: High stress concentration zone during tank filling and emptying cycles.
Key Concepts to Memorize for Exams
✓Bottom shell course (Course 1) carries highest hydrostatic liquid load.
✓Annular plates form the critical structural foundation ring of the tank.

Module Knowledge-Check Quiz

Question 1: Which shell course on an atmospheric storage tank experiences the greatest hydrostatic pressure?
Module 1 of 4