Last update: Jan 13, 2017
High Temperature Hydrogen Attack (HTHA) is an insidious condition that can occur in process equipment 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. The atomic hydrogen then reacts with unstable carbides in steel to form methane gas, which accumulates in the microstructural grain boundaries, eventually leading to cracking. This is often hazardous as the equipment usually contains hydrocarbons at high pressures and temperatures.
HTHA is a time-temperature-pressure dependent phenomenon. This means the longer that a piece of equipment is exposed to temperatures and hydrogen partial pressures above its resistance limit, 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.
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. 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 areas of concern for HTHA. Welds often suffer from HTHA degradation as well.
Typically HTHA can be avoided by choosing the proper alloy steel or stainless steel cladding to resist the combination of hydrogen partial pressure and temperature, or by adjusting the operating conditions to stay below the Nelson Curve limit for the existing materials of construction. However, there have been several cases where HTHA was found even though operating conditions were below the Nelson Curve.
It can often be difficult to predict the specific areas to inspect for HTHA, since the damage can be very localized. A corrosion or materials specialist, experienced in this particular phenomenon, should be consulted for identifying susceptible equipment, selecting inspection locations, and estimating remaining life of equipment in this service.
Inspection techniques for finding advanced stages of HTHA at the surface include WFMT, MT, and in-situ metallography (e.g., field metallographic replication). Advanced ultrasonic backscatter testing (AUBT) has also been successfully used to find earlier stages of HTHA.
Are you interested in learning more about HTHA? Inspectioneering has created an Asset Intelligence Report (AIR) called A Primer on High Temperature Hydrogen Attack. The report is free to download; simply click the button below to get it.
Recommend changes or revisions to this definition.
January/February 2016 Inspectioneering Journal
By Greg Alvarado at Inspectioneering Journal
The enormous decline in oil prices over the past 14 months has definitely slowed projects and changed the energy and production landscape. Despite this, refineries, petrochemical plants, and chemical facilities must continue to run safely, responsibly, and reliably.
November/December 2015 Inspectioneering Journal
By Ralph E. King P.E. at Stress Engineering Services, Inc., and Brian Olson at Stress Engineering Services Inc.
To ensure the mechanical integrity and fitness-for-service (FFS) of equipment, facility managers, reliability engineers, and inspection technicians must understand the HTHA damage mechanism.
November/December 2004 Inspectioneering Journal
Accounts with shop validation on carbon steel samples prior to field trials, on an in-service C 1/2 Mo vessel, were reported at a recent industry conference. The studies were successful in the laboratory and appear to make sense in field trials on a C 1/2 Mo, in-service vessel.
November/December 2010 Inspectioneering Journal
The following references are from the American Petroleum Institute. They are widely used in the petroleum refining and petrochemical industries for managing equipment in HTHA service and are available in the public domain.
July/August 2012 Inspectioneering Journal
We have recently learned of one organized joint industry project (JIP) that was announced at the Spring 2012 API Refining meeting. As information has become available we have decided to present it to our readership.
November/December 2014 Inspectioneering Journal
By Gerrit M. Buchheim, P.E. at Becht Engineering Co., Inc.
High Temperature Hydrogen Attack (HTHA) is a complex damage mechanism that continues to defy investigators trying to make predictions on the anticipated degree of damage or service life. This article provides some background on HTHA, discusses some current developments in HTHA inspection and mitigation, and describes how one Refiner is instituting an HTHA risk management plan for its refineries and the challenges and pitfalls they have encountered.
AET is a powerful, non-intrusive inspection technique to verify the structural integrity of pressure vessels, spheres, high-temperature reactors and piping, coke drums, above-ground storage tanks, cryogenic storage tanks, and more.
October 28, 2014
U.S. Chemical Safety Board safety video discussing the fatal April 2, 2010, explosion and fire at the Tesoro refinery in Anacortes, Washington. A nearly 40-year-old heat exchanger violently ruptured, causing an explosion and fire that fatally injured seven workers – the largest loss of life at a U.S. refinery since 2005.
September 15, 2014 By Nick Schmoyer at Inspectioneering
I've crunched some numbers and have come up with the three most popular damage mechanisms, based on the activity of our readers, that Inspectioneering publishes information on. I've limited the list to these three mechanisms for the sake of brevity, but keep in mind that there are nearly a hundred different damage mechanisms that affect fixed equipment mechanical integrity in the oil & gas and chemical industries.
July 16, 2014
If you're not already aware, Inspectioneering has started publishing Asset Intelligence Reports, condensed primers and overviews for various topics related to asset integrity management and inspection. The first report was published and made available last week, covering magnetic particle testing. If you haven't downloaded it already, you can do so here.
March 3, 2014 By Greg Alvarado at Inspectioneering Journal
The following question was posed by a member of the Inspectioneering Community: I am working in a fertilizer plant and our inspection team is very new. I was wondering if professionals in similar plants could share their knowledge related to inspection work. Please elaborate on details about the inspection function, as well as the main subjects we should focus on.
January/February 2014 Inspectioneering Journal
By Mike Urzendowski at Valero Energy
The intent of these two articles is to share lessons learned from recent experiences setting up a comprehensive HTHA review process across multiple refineries, and to help other operators define and mitigate the HTHA risk to an acceptable level.
January 30, 2014
The U.S. Chemical Safety Board has released a computer animation recreating the explosion and fire that killed seven workers at the Tesoro Refinery in Anacortes, Washington on April 2, 2010. The five-minute animation illustrates the process of "high temperature hydrogen attack," which over the years damaged and weakened a nearly forty-year-old carbon steel heat exchanger, leading to a catastrophic rupture on the night of the accident.
January 20, 2014
Last week we mentioned three important tips to consider when addressing high temperature hydrogen attack (HTHA). This week, we'd like to provide the reader with a few helpful resources that deal with the topic of HTHA.
January 13, 2014
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.
November/December 2013 Inspectioneering Journal
By Mike Urzendowski at Valero Energy
A recent High Temperature Hydrogen Attack (HTHA) failure atarefineryinthestateofWashingtonwasa“wakeupcall” to our industry. On April 2, 2010, the shell of a feed-effluent heat exchanger in the Naphtha Hydrotreating (NHT) unit at the Tesoro Anacortes WA refinery ruptured, ultimately resulting in seven fatalities.
The goal of asset management is to effectively manage corporate assets in order to gain maximum value, profitability and returns, while safeguarding personnel, the community, and the environment. A true Asset Integrity Management program incorporates...