# Investigation of Multi-Factor Stress Corrosion Cracking Failure of Safe-End Feedwater Lines of Submarine Power System

## TL;DR

This study identifies how a combination of corrosion, stress, and fluid flow leads to failures in submarine power system feedwater lines.

## Contribution

The paper reveals the combined effect of galvanic corrosion, residual stress, and flow velocity in causing stress corrosion cracking in submarine feedwater lines.

## Key findings

- Galvanic corrosion between 20 steel and 316L stainless steel initiates pitting on the 20 steel side.
- Vortex flow around welds accelerates pit growth in multiple directions.
- Residual stress increases the likelihood of stress corrosion cracking along the weld line.

## Abstract

The corrosion process under the complex safe-end feedwater line conditions was investigated via experimental lab testing and numerical simulation. The corrosion of safe-end feedwater lines was controlled through the combination of galvanic corrosion, residual stress, and flow velocity. Firstly, galvanic corrosion occurred once the 20 steel was welded with 316L stainless steel. The pitting corrosion could be observed on the 20 steel side of the weld joint. Secondly, a vortex flow was detected around the welding bump and within the pits. The growth of the pits was accelerated in both the vertical and horizontal directions. Finally, under the residual stress condition, the stress intensity factor (K) at the bottom of the pits was easier to reach than the critical stress intensity factor (KISCC). Then, pitting was transformed into stress corrosion cracking which then propagated along the weld line. Therefore, the critical factor inducing the failure of safe-end feedwater lines was the combined action of galvanic corrosion, residual stress, and flow velocity.