Storage Engineering Design & Integrity Services

Full storage tank Engineering, design and drafting services

Are visual API 653 inspections, partnered with NDE’s, sufficient to determine tank integrity?

When performing tank inspections, per API 653, visual and NDT is performed stringently, with tank settlement typically overlooked. Tanks being flexible steel structures are prone to adjust/settle to its natural environment, foundations, product usage, miss management etc., it is imperative to accurately measure and analyze the full scope of settlement criteria in order to properly manage and maintain tankage assets.

Tank Settlement Criteria

  • Tank shell roundness     API 653
  • Tank shell verticality     API 653
  • Edge settlement        API 653
  • Differential settlement     EEMUA 159
  • Out-of-plane settlement     API 653 & EEMUA 159Floor settlement (remote & localized depressions or bulges)    API 653
  • Floor sagging         EEMUA 159


Tank Shell Roundness

Tank shell roundness basically entails the shell deflection / distortion between adjacent shell locations throughout the height of the tank shell relative to a known reference circumference of the first course. With the coordinated points a centroid is plotted in order to determine the true mean tank centre.


Tank Shell Verticality
Tank shell verticality essentially entails the shell plumbness, in a straight vertical plane, between the shell bottom and shell top. The vertical offset deviance evidently then exists as the tank shell verticality.


Edge Settlement
The shell-to-floor (edge) settlement basically entails the shell deflection / distortion between adjacent shell locations throughout the height of the tank shell relative to a known reference circumference of the first course. With the coordinated points a centroid is plotted in order to determine the true mean tank centre.



Floor Settlement
The floor settlement (bulges or depressions), localized or remote from shell, is measured in accordance with API 653, Figure B.8 or B.9 and analyzed per Figure B.10. (*Floor settlement is not possible due to insufficient internal access to tank floor whilst tanks are in-service.)


Floor Sagging
The floor sagging is measured and analyzed in accordance with EEMUA 159, 7.5.4.
(*Floor sagging is not possible due to insufficient internal access to tank floor whilst tanks are in-service.)


Out-of-plane Settlement (Deferential settlement)