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Corrosion Failure Analysis of Corrugated UNS N10276 and Stainless Steel Flex Hoses

Picture for Corrosion Failure Analysis of Corrugated UNS N10276 and Stainless Steel Flex Hoses
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Product Number: 51321-16649-SG
Author: Surech Divi; Sri Krishna Chimbli
Publication Date: 2021
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Flex hoses constructed from corrosion resistant alloys (CRAs) are commonly used to
supply fuel gas to heat recovery steam generators (HRSGs) in plants. Due to their
availability and relatively low cost, 304L/316L stainless steels (SS) are commonly used in
flex hoses in these applications. However, due to the harsh nature of the fuel gases and
the associated high temperatures, the service life of 304L SS is often shorter than desired.
In particular, longitudinal welds in these hoses become susceptible to corrosion that can
eventually lead to leakage.
This paper describes the failure analysis of a 3-inch (76-mm) 304L SS corrugated flex
hose that developed leaks along its longitudinal weld. It was subsequently replaced by a
N10276 hose, which remained in the same service for approximately 1 year before being
retrieved for examination. The failure analysis included visual examination, photography
and macrophotography, sectioning, analysis of deposits and corrosion products,
quantitative chemical analysis, metallography, scanning electron microscopy, and energy
dispersive x-ray spectroscopy. A metallurgical analysis of the weld microstructure was
also performed for both materials.
The analyses showed that the 304L SS flex hose ruptured along its longitudinal weld due
to excessive corrosion caused by high concentrations of chloride. By contrast, no evident
pits or corrosion formed on the inside surface of the N10276 corrugated hose, indicating
that N10276 provides good corrosion resistance in fuel gas service.

Flex hoses constructed from corrosion resistant alloys (CRAs) are commonly used to
supply fuel gas to heat recovery steam generators (HRSGs) in plants. Due to their
availability and relatively low cost, 304L/316L stainless steels (SS) are commonly used in
flex hoses in these applications. However, due to the harsh nature of the fuel gases and
the associated high temperatures, the service life of 304L SS is often shorter than desired.
In particular, longitudinal welds in these hoses become susceptible to corrosion that can
eventually lead to leakage.
This paper describes the failure analysis of a 3-inch (76-mm) 304L SS corrugated flex
hose that developed leaks along its longitudinal weld. It was subsequently replaced by a
N10276 hose, which remained in the same service for approximately 1 year before being
retrieved for examination. The failure analysis included visual examination, photography
and macrophotography, sectioning, analysis of deposits and corrosion products,
quantitative chemical analysis, metallography, scanning electron microscopy, and energy
dispersive x-ray spectroscopy. A metallurgical analysis of the weld microstructure was
also performed for both materials.
The analyses showed that the 304L SS flex hose ruptured along its longitudinal weld due
to excessive corrosion caused by high concentrations of chloride. By contrast, no evident
pits or corrosion formed on the inside surface of the N10276 corrugated hose, indicating
that N10276 provides good corrosion resistance in fuel gas service.

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