TRACK: Sustainability/Reliability
When the heat exchanger design requires the use of U-bend tubes, these can be subject to U-bend heat treatment per design code. Requirements are typically based on the steel grade, bend radius and special applications such as sour or wet hydrogen sulfide service. API 660 specification stated that heat treatment shall be completed by electric resistance or furnace methods. In some cases, vendor specification may further define the temperature range by the heating method and holding time at the temperature. Even one of the main purposes of the U-bend heat treatment is to limit the residual stress, which can induce susceptibility to stress corrosion, but there is no clear recommendation of the actual stress limit or measurement methods other than annealing requirement. This paper provides the fundamental information for stress distribution pattern during bending, temperature ranges by U-bend section during resistance heat treatment. Indirect residual stress measurement methods are reviewed, which can provide an option of using variable data to define stress limitation rather than using process parameter requirement of temperature and time. The experimental test also provides residual stress amount measured by hardness per bend radii and by the heat-treating temperatures for the alloys of carbon steel, austenitic stainless, duplex and nickel copper alloy.
MTI Global Solutions Symposium 2024
February 26-29
Baton Rouge, LA
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