Inspectioneering Journal

High Temperature Hydrogen Attack Recent Progress and Where To Aim Joint Industry Activities

This article appears in the November/December 2010 issue of Inspectioneering Journal.

Understanding, predicting, detecting and controlling high-temperature hydrogen attack (HTHA), have been elusive goals of materials engineers and scientists for over 70 years. The destruction of low alloy steel components exposed to hydrogen through the formation in the microstructure of high-pressure methane bubbles has led to many failures, fires, and sometimes deaths. The Nelson Curves in API 941 were developed based on remarkable judgment and very limited data over 50 years ago. They have served a limited role for the petroleum industry, a guide to materials selection, but little else.

Nelsons curves were not derived based on detailed and coherent concepts of materials properties, reaction kinetics and thermodynamics. In fact the reason for the largely vertical and horizontal lines was the subject of much speculation and controversy for decades. Nelson was smart enough to plot experience without prejudice.

Regarding HTHA, he left open questions about when, where how much and how fast. Problems that arose with carbon 1⁄2- moly steels more than a decade ago underscored the lack of predictability of behavior and gave rise to needs for fitness-for-service (FFS), risk based inspections (RBI) and improved NDE techniques. Some progress has been made in these areas, but the problem is far from mastered.

Methane bubbles form on grain boundaries which weaken the steel
Methane bubbles form on grain boundaries which weaken the steel

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