# Predictive Correlation Between Hardness and Tensile Properties of Submerged Arc Welded API X70 Steel

## TL;DR

This study shows that hardness measurements in welded API X70 steel can predict tensile properties, helping improve pipeline safety and weld quality.

## Contribution

The paper introduces empirical models linking hardness and tensile properties in submerged arc welded API X70 steel.

## Key findings

- Fusion zone hardness correlates strongly with tensile strength (R2 = 82%).
- Base metal hardness significantly affects yield strength (R2 = 71%).
- Hardness has a moderate negative correlation with elongation (R2 = 54%).

## Abstract

This research investigates the statistical correlation between Vickers hardness and tensile properties of helical submerged arc welded high-strength low-alloy (HSLA) API X70 pipeline steel. Tensile tests were performed on cross-weld joints from 138 pipe specimens. Vickers hardness measurements were also conducted on 138 samples to evaluate the hardness distribution across the base metal, fusion zone, and heat-affected zone. Results show that the fusion zone exhibits the highest hardness, correlating with enhanced tensile strength (R2 = 82%). Linear regression models indicate that base metal hardness significantly influences yield strength (R2 = 71%), while moderate negative correlations exist with elongation (R2 = 54%). These findings suggest that hardness measurements can serve as a non-destructive predictive tool for tensile properties, improving weld quality and mechanical performance. This research provides empirical models that enhance the application of API X70 in critical engineering applications, improving pipeline safety and reliability.