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Type: Artigo de periódico
Title: Application of acoustoelasticity to evaluate stress relaxation in API 5L x70 steel for pipelines
Author: Santos, AA
Bray, DE
Andrino, MH
Trevisan, RE
Abstract: API 5L x70 steel is used in long distance gas pipelines. The manufacturing procedure of tubes can introduce residual stresses into them. If these components are loaded with stress in service, the final value of the stress inside the part will be unknown. Knowing that the stresses can decrease With time without a stress relief process would allow designers to enhance the design codes. Although relaxation at low temperatures is not well known amongst current researchers, previous work performed in steel by Moffatt (1951) and Chance (2000) proved that residual stresses in welded joints can be reduced over time. This present work shows the application of an ultrasonic technique to verify stress relaxation in API 5L x70 plates. A special geometry was developed, so that each plate has uniaxial stress in the measurement region. Sixteen plates were tested, eight in the rolling direction and the remaining in the orthogonal direction. The plates were stress relieved using an initial heat treatment to set a stress free reference state. After that, they were welded to create the stress field in the area of investigation. A final step was to cut each one of the samples at specific intervals after the welding. After each step, the stress was measured with ultrasound in the uniaxial stress region. A record of the process was precisely established at the time Of each step. The differences in the acoustoelastic constants with rolling direction and the variation of the Young's modulus were taken into account. The results showed clear effects of relaxation in those samples. The magnitude was much more pronounced than in UNS G10100 steel.
Subject: ultrasonic stress test
weld stresses
oil pipe failures
nondestructive testing
Country: EUA
Editor: Amer Soc Nondestructive Test
Rights: fechado
Date Issue: 2005
Appears in Collections:Artigos e Materiais de Revistas Científicas - Unicamp

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