ASTM G158-23
Standard Guide for Three Methods of Assessing Buried Steel Tanks

Standard No.

ASTM G158-23

Release Date

2024

Published By

American Society for Testing and Materials (ASTM)  US  /  ASTM

Replace By

ASTM G158-98(2021)

Latest

ASTM G158-98(2021)

Introduction

Standard Technical Background and Evolution

Since its initial publication in 1998, ASTM G158 has undergone revisions from the 2021 edition to the 2023 edition, gradually improving the methodology for corrosion assessment of underground steel storage tanks (USTs). This standard complements other standards, such as NACE SP0285 and EPA SW-846, to form a technical framework for tank integrity management.

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Comparison of three core evaluation methods

Evaluation dimensions	Method A (non-invasive)	Method B (ultrasonic thickness measurement)	Method C (visual inspection)
Technical principles	Statistical model prediction based on soil electrochemical parameters	Combination of ultrasonic measured wall thickness and corrosion environment analysis	High-definition image recording + corrosion product morphology analysis
Detection coverage	Area surrounding the drilling point	≥15% internal surface area	≥98% internal surface area
Accuracy requirements	Failure prediction standard deviation ≤ 1.5 years	Thickness measurement accuracy ±0.25mm	Corrosion pits ≥ 3mm can be identified
Applicable scenarios	Preliminary screening/low-risk tanks	Medium corrosion risk verification	High-risk or old tanks

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Key implementation points

Method A execution process

1. Arrange diagonal drill holes according to clause 9.1.2 (at least 2 holes for every 4 tanks)
2. Measure soil resistivity in layers (Test Method
3. Laboratory analysis of corrosion factors such as Cl^- and S^2- (EPA SW-846)
4. Input into the multivariate regression model: E(Age)=f(R,M,Cl,pH,S,SC,TS,P)

Acceptance criteria

• Probability of corrosion perforation <0.05 (Clause 9.3.3)
• Tank age < predicted zero leakage life (Clause 9.3.2)
• Sealing test is required within 3-6 months after cathodic protection is installed (Clause 9.3.4)

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Analysis of technical difficulties

Model Validation Requirements: Standard 9.2.2.3 specifies that the statistical model must be validated based on data from ≥200 actual excavated tanks, and must include a balanced distribution of leaking and non-leaking samples.

Ultrasonic Testing Limitations: Clause 10.2.6 states that when a dense oxide layer forms on the inner wall of a tank, an ultrasonic probe capable of penetrating a 0.125mm defect must be used, and the measurement position error must be controlled within 5% of the maximum dimension of the tank.

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Recommendations for Standard Application

Method Selection Matrix

Can Age	Soil Corrosivity	Recommended Method
<10 Years	Low (Resistivity >5000Ω·cm)	Method A
10-20 Years	Medium (500-3000Ω·cm)	Method B
>20 Years	High (Contains SRB)	Method C

Compliance Management

In accordance with Chapter 6 of the standard, all assessments must be supervised by a NACE-certified cathodic protection expert, who must issue a written certification document (see Appendix A1 Third-Party Verification Form).