Thermal Fatigue

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Overview of Thermal Fatigue

Thermal Fatigue is a specific type of fatigue failure mechanism that is induced by cyclic stresses from repetitive fluctuations in the temperature of equipment. The degree of damage is affected by the magnitude and frequency of the temperature swings. Damage typically appears in the form of one or more cracks at the surface of the component. Unless remedied, cracks may propagate through the material eventually leading to failure.

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All materials of construction and several types of units and equipment can be affected by thermal fatigue. A few include:

Hot and cold stream mixing points
Areas where condensate and steam systems contact each other
Coke drum shells and skirts
Steam generating equipment
High temperature superheater and reheater tubes

Prevention, Inspection & Mitigation

The best way to prevent failure due to thermal fatigue is to minimize thermal stresses and cycling in the design and operating of equipment. Reducing stress raisers, controlling temperature fluctuations (especially during shutdown and start-up), and reducing thermal gradients can help prevent thermal fatigue. Taking proactive measures to prevent cool liquid from touching hot boundary walls, e.g. installing liners or sleeves, can also prove effective. This event occurs as products travel downstream from one processing unit to the next where successive units may operate at various temperatures.

Unfortunately, thermal fatigue cannot always be prevented. As a result, there are several ways to inspect for and mitigate thermal fatigue, including:

Visual inspection, liquid penetrant testing (PT), and magnetic particle testing (MPT) for inspection of equipment surfaces.
Surface wave ultrasonic testing (SWUT) and other ultrasonics can be utilized as non-intrusive methods of testing for internal cracks.

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Articles about Thermal Fatigue

Damage Control: Thermal Fatigue Mitigation

January/February 2021 Inspectioneering Journal

Thermal fatigue, a specific form of fatigue driven by varying metal temperature gradients and ensuing differential thermal expansion, is generally most effectively mitigated by reducing the severity of metal temperature gradients.

Authors: Phillip E. Prueter

Damage Control: Thermal Fatigue Assessment

November/December 2020 Inspectioneering Journal

Conventionally, three primary fatigue analysis methods have been used to estimate fatigue life; these are the stress-life (S-N) approach, the strain-life (ε-N) approach, and the fracture mechanics (crack growth) approach.

Authors: Phillip E. Prueter

Damage Control: Thermal Fatigue Detection

September/October 2020 Inspectioneering Journal

This article reflects the first in a series on damage mechanisms that will appear in this recurring Inspectioneering column entitled “Damage Control.” The inaugural topic discussed in this column is thermal fatigue.

Authors: Phillip E. Prueter

Thermal Fatigue - A Quest for Asset Integrity

January/February 2020 Inspectioneering Journal

This article addresses two failure events where inadequate attention to thermal fatigue led to premature equipment failure while specifying guidelines to help prevent such failures that can be a part of a plant's inspection and maintenance programs.

Authors: Ahmad RK Rana, Dr. Zoheir Farhat

FFS Forum: Fatigue Mitigation Strategies

January/February 2020 Inspectioneering Journal

There are many sources and occurrences of metal fatigue in the chemical and refining industries. They range from low-cycle thermal stresses in an FCCU, to the relentless pressure cycling of a PSA, to the ultra-high cycles of a rotating pump.

Authors: Greg Garic

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High-Energy Piping Systems: Avoid Cracking Under Pressure

January/February 2015 Inspectioneering Journal

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Authors: Pamela Hamblin

Criticality Assessment of Piping Systems for Oil & Gas Facilities

May/June 2014 Inspectioneering Journal

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Authors: Fernando Vicente