Fitness-for-service assessment for pressurized components

• Main Author: Ong, Yun Wei.
• Other Authors: Ong Lin Seng
• Format: Final Year Project
• Language: English
• Published: 2009
• Subjects: DRNTU::Engineering::Mechanical engineering::Control engineering
• Online Access: http://hdl.handle.net/10356/16132
• Institution: Nanyang Technological University

In the refining and petrochemical industry, safety has always been the upmost concern to any organization. As infrastructures in-service age, degradation or damage may affect the structural integrity posing a threat to safety. One of the common flaw types is geometrical imperfections such as welding misalignment, shell distortions which can result in residual stresses and additional bending stresses existing within the structure. These infrastructures comprise of pressure vessels, piping and tankage, replacement is normally difficult due to size and cost considerations. Hence organizations would invest substantially in maintenance of these infrastructures. For ensuring the structural integrity, the method used commonly is a Fitness-For-Service (FFS) assessment. It is a quantitative engineering evaluation that is performed to demonstrate the structural integrity of an in-service component containing a flaw and is documented in API RP 579. The purpose of API RP 579 is the provision of safety to plant personnel and the public, Fitness-For-Service assessment procedure for various types of damage, and optimization of existing facilities while improving long–term economic feasibility. The focus of this project would be on the assessment of geometric imperfections weld misalignment and shell distortions subjected to internal pressure. Investigation of the technical basis for Fitness-For-Service assessment procedures would be carried out by literature review of the theory and program automation of the procedures using Microsoft Excel. Area covered in the literature review includes welding distortion and residual stress, API Recommended Practice 579, weld misalignment and shell distortions. After which validation of the Excel program was made using two API RP 579 example problems. Finite element method analyses were carried out for the two example problems as a final verification. Being generally recognized to give more accurate results, the Maximum Distortion Energy Yield Criterion was used to establish the stress intensity in the FEM analyses. In conclusion, program automation of the assessment procedures provided a time efficient mean of assessment for the user. Recommendations include further improvement of the Excel program through Visual Basic Macros and possible improvement to the assessment procedures. In addition, a FEM analysis is recommended when dealing with critical area or component as it provides more accurate and area specific information with regards to the flaw.