Inspectioneering
Blog

Three Tips for Addressing High Temperature Hydrogen Attack

By Jeremiah Wooten, Managing Partner at Inspectioneering. January 13, 2014
2 Likes

One of Inspectioneering's editorial themes this month is High Temperature Hydrogen Attack (HTHA). It is a highly contentious issue that the industry is still struggling to fully understand. If you have any questions or experiences with HTHA that you would like to share with the Inspectioneering community, please feel free to post a comment below. Here are three tips for addressing HTHA at your facility.

1. Know what you are dealing with. 

High Temperature Hydrogen Attack (HTHA) is an insidious condition that can occur in process equipment that is exposed to hydrogen at elevated temperatures (at least 400F or 204C), under dry conditions, when hydrogen disassociates into nascent (atomic) hydrogen, which is then driven into the steel by the temperature and pressure of the environment. That atomic hydrogen then reacts with unstable carbides in steel to form methane gas, which then causes hydrogen gas pockets to form that leads to material degradation, cracking, and failure.

2. Do not underestimate its potential severity.

HTHA is a time-temperature-pressure function, which basically means the longer that a piece of equipment is exposed to temperatures above its resistance limit in a certain hydro-process environment, the more damage to the steel will accumulate; and the higher the temperature rises above the limit of the steel, the more rapidly the damage will occur.  The damage that results from HTHA ranges all the way from superficial surface decarburization of the ID surface to severe material embrittlement, loss of mechanical properties, and cracking.  This degradation has led to catastrophic equipment failures, some involving multiple fatalities, such as the tragic event in a Pacific Northwest refinery back in 2010, when a heat exchanger shell burst open during operation.

3. Know where to look for it.  

HTHA affects carbon and low alloy steels, but is most commonly found in carbon steel and carbon-1/2 Mo steel that is operating above its corresponding Nelson Curve limits.  However, there is now a building body of evidence that carbon steel, like carbon ½ Mo before it, may suffer HTHA below its current Nelson curve. Areas that are hotter, often near the outlet nozzle of catalytic equipment or the inlet nozzle of an exchanger that is cooling the process, are two specific areas of concern for HTHA. In addition, welds often suffer from HTHA degradation preferentially in the HAZ, especially if they are not postweld heat treated.


The information provided above has been derived from several past articles in Inspectioneering Journal, including those listed below.  They make it clear that the potential for HTHA should be taken very seriously. We recommend reading additional material on the subject, as we have only begun to scratch the surface in this Blog. Here are links to a few articles published in Inspectioneering Journal that cover HTHA:


Interested in reading more about high temperature hydrogen attack, corrosion and materials, and many other asset integrity management topics? Click the button below to download a free copy of John Reynold's updated and revised 101 Essential Elements in a Pressure Equipment Integrity Management Program guide.


Comments and Discussion

There are no comments yet.

Add a Comment

Please log in or register to participate in comments and discussions.


Inspectioneering Journal

Explore over 20 years of articles written by our team of subject matter experts.

Company Directory

Find relevant products, services, and technologies.

Training Solutions

Improve your skills in key mechanical integrity subjects.

Case Studies

Learn from the experience of others in the industry.

Integripedia

Inspectioneering's index of mechanical integrity topics – built by you.

Industry News

Stay up-to-date with the latest inspection and asset integrity management news.

Blog

Read short articles and insights authored by industry experts.

Expert Interviews

Inspectioneering's archive of interviews with industry subject matter experts.

Event Calendar

Find upcoming conferences, training sessions, online events, and more.

Downloads

Downloadable eBooks, Asset Intelligence Reports, checklists, white papers, and more.

Videos & Webinars

Watch educational and informative videos directly related to your profession.

Acronyms

Commonly used asset integrity management and inspection acronyms.