Brittle Fracture

Explore this topic

Brittle Fracture is the sudden, very rapid cracking of equipment under stress where the material exhibited little or no evidence of ductility or plastic degradation before the fracture occurs. Unlike most other tensile failures, where the material plastically strains under overload conditions and becomes thinner until the point of rupture, when a piece of equipment suffers a brittle fracture, there is no thinning or necking down. Rather, this damage mechanism often causes cracking without warning, sometimes fracturing equipment into many pieces.

Brittle fracture is often caused by low temperatures. If the steel temperature is at or below its ductile-to-brittle transition temperature (DBTT), then it will be susceptible to brittle fracture. Combine this with a critical sized flaw and high stress on that flaw (either applied or residual), and then you are likely to experience a brittle fracture.

Other factors that can increase the susceptibility to brittle fracture include:

Metallurgical Degradation

Metallurgical degradation can occur in some steels at higher temperatures and can include things like temper embrittlement, graphitization, sigma phase embrittlement, and 885 embrittlement.

Steel Cleanliness and Grain Structure

As for steel cleanliness and grain structure, large grain sizes and steel contaminants can reduce steel toughness, so it's important to be aware and mindful of this during material selection amd QA/QC.

High Material Thickness

When it comes to material thickness, thicker components have a higher degree of susceptibility to brittle fracture because they have higher tri-axial stresses. Also, thicker materials produce a state of higher constraint, and are therefore less likely to deform under stress as opposed to crack initiation and propagation.

Colder Operating Temperatures

Operating an equipment or piping at temperatures colder than its lower design temperature (LDT, also known as Minimum Design Metal Temperature or MDMT in ASME codes) at sufficient operating pressure can also cause brittle fracture. Hence it is always important to operate an equipment/piping within its design limits. API RP 579 part-3, "Assessment of Existing Equipment for Brittle Fracture" provides guidelines to check if an equipment can be operated at temperatures colder than LDT, without brittle fracture damage to the equipment.

Types of Brittle Fracture

There are two major types of brittle fractures: transgranular and intergranular. With transgranular fractures, the fracture travels through the grain of the material. It changes direction from grain to grain due to the different lattice orientation of atoms in each grain, following the path of least resistance. Intergranular fracture, on the other hand, occurs when the a crack travels along the grain boundaries, as opposed to through the grains themselves. Intergranular fracture usually occurs when the phase in the grain boundary is weak and brittle.

Brittle Fracture Prevention/Mitigation

In order to reduce the risk of brittle fracture, one must be sure to keep materials operating at or above their DBTT during both service and testing. Likewise while conducting repairs, taking steps to establish and find flaws that might weaken the material while in-service or during pressure testing will reduce the chances of brittle fracture. This topic is covered in more detail in API RP 571 - Damage Mechanisms Affecting Fixed Equipment in the Refining Industry.

Related Topics

Relevant Links

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 Brittle Fracture
January/February 2024 Inspectioneering Journal

The final installment of the series concludes by providing practical insight into common brittle fracture and ductile tearing mitigation strategies.

November/December 2023 Inspectioneering Journal

Part 2 of this three-part series on brittle fracture focuses on methods for evaluating the risk in pressure equipment and the evolution of screening and assessment methods.

September/October 2023 Inspectioneering Journal

This article is Part 1 of a new three-part series on brittle fracture and focuses on the fundamental concepts and damage morphology associated with the unstable rupture of pressure equipment.

January/February 2023 Inspectioneering Journal

Ferritic materials change in toughness as a function of temperature, but the change is non-linear and happens at different temperatures for different materials.

Authors: Greg Garic, P.E.
November/December 2022 Inspectioneering Journal

Discussion on the new Annex 9J procedure with examples using the Part 3 exemption curve, the 9J General Procedure, and the 9J Simple Procedure.

Authors: Greg Garic, P.E.
Partner Content

Traditional pressure vessel inspections often require taking assets out of service. However, MISTRAS’ Non-Intrusive Inspection (NII) programs provide data as good or better than internal inspections, while assets remain in service. NII is...

May/June 2022 Inspectioneering Journal

Part 2 of the three-part series on stress corrosion cracking (SCC) that examines common engineering and FFS methods that can be leveraged to understand and evaluate the propensity for an existing form of SCC to lead to loss of containment.

May/June 2020 Inspectioneering Journal

This article provides an overview of brittle fracture, details on several industry failures, and a summary of deficiencies and concerns with current published methods for screening susceptibility of equipment to potential brittle fracture failures.

May/June 2020 Inspectioneering Journal

There are many places where brittle fracture risk can sneak into your plant and many reasons why a new or revised brittle fracture assessment may be required when reviewing your pressure systems. Don’t overlook this dangerous failure mechanism.

Authors: Greg Garic, P.E.
March/April 2019 Inspectioneering Journal

Brittle fracture and material toughness issues are important concerns in equipment design and FFS. These issues increase when temporary start-up and shutdown conditions require more detailed assessments than provided for in vessel and piping codes.

Authors: Greg Garic, P.E.
May/June 2018 Inspectioneering Journal

There is concern in the industry over recent findings of reduced toughness fittings and flanges at risk of brittle fracture. This article provides an overview; possible contributors; measures taken to address; and a proposed FFS approach to address...

Partner Content

Ethos has assembled a team of experts who apply what they learned through years of process safety experience in the industry and dealing with OSHA and EPA. Click here to learn more about our services.

January/February 2018 Inspectioneering Journal

Given the concern throughout industry regarding the potential for brittle fracture failures, PWHT guidance to address potential issues arising from the recent changes in PWHT code requirements for carbon steel is examined in this article, and...

November/December 2017 Inspectioneering Journal

In-service equipment failures present a considerable challenge to reliability engineers. This article presents a case study of a convection tube failure in a furnace and the analyses that were performed to understand the root cause and determine the...

Authors: James R. Widrig
January/February 2014 Inspectioneering Journal

Inspections, repairs, modifications, or Fitness-For-Service (FFS) assessments on an old, unfired ASME Section VIII (Div. 1) pressure vessel - Which ASME Section VIII (Div. 1) Code Edition should you use?

November/December 2013 Inspectioneering Journal

Service failures and safety incidents of machines, structures, and pressure equipment have been experienced in the oil and gas industry for many years without warning, with varying degrees of consequential damages to health, safety,...

Authors: Fernando Vicente
November/December 2013 Inspectioneering Journal

Auto-refrigeration is a process where an unintentional and/or uncontrolled phase change of a hydrocarbon from a liquid state to a vapor occurs, resulting in a very rapid chilling (refrigeration) of the liquid containing local equipment and/or...

Partner Content

Whether you decide for a Computed Radiography scanner with flexible imaging plates or a flat panel detector with the fastest imaging, or even combine the advantages of both technologies, DÜRR NDT's innovative systems offer high reliability and...

January/February 2007 Inspectioneering Journal

In previous parts of this series, I have covered many corrosion and degradation issues, some environmental cracking diseases, metallurgical degradation mechanisms, issues associated with welding and some external corrosion problems. In part 14,...

Authors: John Reynolds
September/October 2005 Inspectioneering Journal

Strain-aging problems are another form of metallurgical degradation and thankfully are not very common and becoming less so; but since strain-aging does still occasionally occur, it still makes the list of one of the “99 diseases of pressure...

Authors: John Reynolds
September/October 2005 Inspectioneering Journal

Another form of metallurgical degradation at higher temperatures is called sigma phase embrittlement. As the name implies, a metallurgical phase change occurs in some stainless steels when they are heated above about 1000F (540C).

Authors: John Reynolds
September/October 2005 Inspectioneering Journal

Titanium (Ti) hydriding is another somewhat unusual metallurgical degradation phenomena that can result in brittle fracture. Unlike many other steel embrittlement phenomena, this one most often occurs in thin wall Ti tubes that have been selected...

Authors: John Reynolds
November/December 2003 Inspectioneering Journal

Hydrogen Embrittlement (HE) is an insidious form of degradation that can strike during equipment fabrication, cleaning, repairs or while in-service. It stems from the infusion of atomic hydrogen into some higher strength steels that then leads to...

Authors: John Reynolds
May/June 2000 Inspectioneering Journal

This is the first of a series of articles that outlines the 101 essential elements that need to be in place, and functioning well, to preserve and protect the reliability and integrity of pressure equipment (vessels, exchangers, furnaces, boilers,...

Authors: John Reynolds
    Videos related to Brittle Fracture
      Training Courses related to Brittle Fracture
        Downloads & Resources related to Brittle Fracture
          News related to Brittle Fracture

            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.


            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.

            Videos & Webinars

            Watch educational and informative videos directly related to your profession.


            Commonly used asset integrity management and inspection acronyms.