Integripedia Topic
Spheroidization (Softening)

Explore this topic

Spheroidization describes a specific change that can occur in the microstructure of carbon and low alloy steels exposed to temperatures from 850°F – 1400°F (440°C – 760°C). This change may result in a loss of mechanical strength and/or resistance to creep.

When exposed to the susceptible temperature range, the elements that strengthen steels (carbide phases) can become unstable and begin to group together, which reduces the strength of the material. At higher temperatures, spheroidization can begin to affect the steel within a matter of hours. At lower temperatures though, spheroidization can take years to have a noticeable effect on the material.

Fortunately, spheroidization isn’t too serious of an issue in most circumstances. The loss of strength is usually minor and doesn’t create any safety issues that might compromise operation of equipment.

In certain rare high temperature situations, the loss of strength can be significant enough (~30%) to result in a reduction in design margin of the equipment. In these cases, fitness for service assessment should be performed to determine the proper course of action.

Expert Insight

The following is from 99 Diseases of Pressure Equipment by John Reynolds. Read the full article here.

Spheroidization is a rather technical term that describes a metallurgical aging phenomena that results in loss of mechanical and creep strength. It occurs when carbon and low alloy steels are exposed to temperatures in the range of 850°F - 1400°F (440°C - 760°C) where carbide phases (the strengthening element of steels) become unstable and begin to agglomerate, which then results in the loss of strength. At the upper end of that temperature range, spheroidization can occur within hours, while at the lower end, it may take years; so it is clearly another of our time- temperature degradation phenomena.

Spheroidization is not much of threat to our pressure equipment, except in some unusual circumstances. Usually the loss of strength is relatively minor, but under some high temperature conditions can cause a 30% reduction in strength. However, that loss of strength usually results in some reduction in design margin, which can sometimes be acceptable for continued safe operation with appropriate fitness-for-service analysis. If it’s not acceptable, then derating is usually the result. The unusual conditions where spheroidization could be a threat involve high stress intensification factors, high applied stresses, or in combination with other degradation or flaws...

Continue reading...

Related Topics

Topic Tools

Share this Topic

Contribute to Definition

We welcome updates to this Integripedia definition from the Inspectioneering community. Click the link below to submit any recommended changes for Inspectioneering's team of editors to review.

Contribute to Definition
Articles about Spheroidization (Softening)
    News related to Spheroidization (Softening)
    • Partner Content

      Gecko's TOKA Flex robot is designed to give unprecedented access to piping systems with a robust ultrasonic data-collection capability. The Flex, our most advanced RUG robot, is equipped to find and collect the critical inspection data you need....

      Inspectioneering Journal

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

      Company Directory

      Find relevant products, services, and technologies.

      Talent Solutions

      Discover job opportunities that match your skillset.

      Case Studies

      Learn from the experience of others in the industry.


      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.


      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.


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


      Watch educational and informative videos directly related to your profession.


      Commonly used asset integrity management and inspection acronyms.