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HTHA Demystified
June 28, 2019

What is HTHA?

High Temperature Hydrogen Attack (HTHA) is a condition that can occur in process equipment exposed to hydrogen at elevated temperatures and pressures over time.  Hydrogen reacts with carbides in steel and can manifest into internal decarburization and fissuring including molecular hydrogen and methane accumulating at grain boundaries.  Subsequent high localized stresses can lead to formation of fissures or cracking in steel, resulting in degradation of mechanical properties. HTHA poses a substantial threat of catastrophic failure if left undetected. The main factors influencing HTHA are hydrogen partial pressure, temperature, the duration of the exposure, and stress.

Carbon and low alloy steels are the most susceptible to HTHA but any process piping and vessels with the above combination are at risk.

Acuren’s HTHA Arsenal

Throughout the industry, conventional methodologies have not proven effective at detecting early stage HTHA.  Acuren has recognized this limitation, and has adopted a suite of advanced NDE screening methodologies that employ the latest in advanced ultrasonic equipment and techniques to accurately diagnose symptoms of HTHA:

64 Element PAUT – High Resolution Phased Array

  • Sound is generated across the active elements when a voltage is applied, with increased firing power/elements, a greater resolution is achieved
  • Greater resolution means the ability to see smaller indications that may not be detected using conventional ultrasonic methods and the ability to discriminate between single or clusters of smaller indications

TOFD – Time of Flight Diffraction

  • Diffraction-based method that measures the reflection of the indication body and diffraction of the sound wave at the indication tips making it a highly sensitive sizing technique
  • A reliable screening tool for the early stages of HTHA
  • Wide coverage area and useful for weld and parent material examinations
  • Small data files
  • Equipment is readily available and cost effective
  • Needs to be performed in conjunction with other NDE methods to verify exact position and indication type

TULA – TOFD Ultra Low Angle

  • Simple but highly sensitive means of detecting HTHA
  • Scan speeds exceed Phased Array and TFM
  • Probes with different specific focal depths
  • Can be used in-lieu of TOFD where there is only room for one probe
  • Operator training is essential

TFM – Total Focus Method

  • Similar to PAUT, except one element fires and all elements listen for reflections
  • Detects defects in many different orientations
  • Good sensitivity to even small defects
  • Very large data files
  • Slower method than TOFD and TULA

Because HTHA inspections aren’t regulated, Acuren’s combination of engineers, specialists and rope access experts can help take the guesswork out of your approach, assist you with designing a program that fits your specific equipment, and minimize your risk profile

In-House Engineering

Our in-house engineers can utilize the findings of the advanced NDE technologies in conjunction with Fit For Service (FFS) API 579 engineering evaluations to determine the best course of action for your assets. If early stage HTHA is suspected, the FFS can quickly resolve if the asset can continue to run, or determine correct inspection methods and intervals for mitigation of risk.

HTHA Specialists


The evaluation of HTHA damage is highly specialized and requires advanced HTHA training which may include 3rd party training or performance demonstration qualification examination recognized by owner/users.  Acuren has more qualified HTHA inspection technicians in Canada and the US than any other NDE provider, a number of whom also hold rope access qualifications. We have the resources (personnel & equipment) to support customers across North America.

Contact us today to help you assess your risk, and design an approach to address your specific areas of concern at info@acuren.com or 1-800-218-7450.

Brochure Download


As the transmission of the COVID-19 virus increases around the world and within our own communities, we want to make our customers aware that, in most jurisdictions, we fall within the essential services exception and we are able to perform the services customers require on their sites. As well we want to take a moment to update you on the measures we continue to implement to ensure business continuity and transmission reduction:

  • We continue to share regular communications with employees to ensure we are providing important news about the status of the virus and the actions taken by the company;
  • The Acuren COVID-19 email address continues to act as a valuable resource to which employees can send questions and concerns, and request other support related to COVID-19;
  • Our single point of contact continues to be a central resource to respond to issues related to the virus and associated company direction;
  • We have responded in real time to take appropriate measures in communities where we are informed of governmental restrictions that have a direct effect on our employees;
  • Alternate work provisions and enhanced infection control practises have been implemented across the business to minimize the potential for spread of the virus in our offices and field work locations;
  • On an almost daily basis we post valuable educational and informational resources on our online portal for the benefit of all North American employees;
  • We regularly remind employees of the critical need to comply with infection prevention and control measures such as frequent hand washing, appropriate respiratory etiquette and instruction to stay home if feeling unwell,
  • We continue to monitor and adjust our inventory of consumables and critical equipment to ensure we are equipped to respond to client needs in the event of a supplier shortage;
  • We have maintained frequent interaction with our leadership team on this matter to ensure we remain fully informed of changing circumstances;
  • We monitor the use of a disclosure form completed prior to employee’s returning to work to identify the presence of any symptoms related to the coronavirus, any personal travel within, or personal contact with travelers to/from, any international location, within the previous 14 days. This has been integrated into our onboarding plan for new projects;
  • We have distributed our Pandemic Plan to address the challenges presented by the current viral spread and to plan for the continuity of our services;
  • We have instituted restrictions on travel that is not business critical and have expanded our use of virtual meeting software.
  • We continue to communicate with our clients regarding the status of our actions, the preparedness of our business, the availability of our workforce, and our express intention to work in partnership to maintain the safety and health of our employees on their sites;
  • We continue to provide instructions related to isolation and quarantine requirements as per the CDC and WHO, and to ensure such requirements are met by affected employees;
  • Where we have employees who test positive for the virus, we have implemented a protocol to ensure all potentially affected parties are notified and proper precautions taken.

Our primary concern is always employee and client safety. To this end, we will continue to add to, or modify, our preparedness program in reaction to this evolving situation. We thank you in advance for all of your efforts in doing the same, and, as always we commit to working with you to ensure a safe worksite for all employees.

Should you have any questions regarding the foregoing, please contact me at (780) 405-5771 or kevin.hill@acuren.com; or Jen Miller at (780) 782-8082 or jen.miller@acuren.com at your earliest convenience.

Best Regards,

Kevin Hill, P.Eng., MBA
Vice President, Commercial
Jen Miller
Director, Human Resources
Acuren Director, COVID-19 Communications
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