The inner diameter of pipes is a critical location for design and performance assessment. Corrosion, fatigue, and stress corrosion cracking often attack the pipe inner diameter, which can lead to leakage and possible failure of the system. Tensile residual stresses in welded pipe joints can have a significant impact on structural integrity and performance because they accelerate crack initiation and growth. In engineering design, understanding the magnitude and distribution of residual stresses on the pipe inner diameter allows accurate structural assessment and planning for inspection. Measuring residual stress on the pipe inner diameter is challenging and provided a unique opportunity to express our commitment to innovation.
Hole drilling is a mature technology for the measurement of near-surface residual stress and has been standardized by ASTM in E837. The method can be applied to quantify the average residual stress over the depth of a drilled hole (typically 1.0 mm depth). While hole drilling is a well-defined method for residual stress measurement, applying it to the inner diameter of pipes comes with additional challenges including placing a strain gage and drilling a hole with limited access for tooling. In order to perform these measurements, Hill Engineering designed and manufactured a special guide tool to allow precise and secure mounting of strain gages in pipes of varying diameter and length. Hill Engineering also developed a miniature precision drilling system that provided measurement access at the pipe inner diameter.
This unique application of a conventional residual stress measurement method provided data for structural integrity assessment of the welded piping system. Prior to the development of this measurement capability, engineering decisions were based on conservative assumptions and large safety margins. The new capability provides reliable measurement data and allows for lower assumed margin.
Hill Engineering has extensive experience with hole drilling, and a reputation for providing high-quality residual stress data. We also offer precise installation of instrumentation in tight spaces, on unique and exotic materials, for complex parts, and in other challenging applications.