Date of Award

Fall 12-15-2012

Degree Type

Dissertation

Degree Name

Ph.D.

Degree Program

Engineering and Applied Science

Department

Naval Architecture and Marine Engineering

Major Professor

Pingsha Dong

Second Advisor

Anna Paradowska

Third Advisor

Dongming Wei

Fourth Advisor

Paul Schilling

Fifth Advisor

Brandon Taravella

Sixth Advisor

Lothar Birk

Abstract

This research sought to establish residual stress distribution characteristics in typical pipe and vessel welds by carrying out a comprehensive parametric study using an advanced sequentially coupled thermo-mechanical finite element procedure. The parametric study covered vessel and pipe components with a ranging radius to thickness ratio from r/t=2 to 100, for thickness ranging from t=1/4” to 10”. Component materials varied from low carbon steel to high alloy steels, such as stainless steel and titanium alloy. Furthermore, a structural mechanics based framework is proposed to generalize through-thickness residual stress distributions for a broad spectrum of joint geometry and welding conditions. The results of this study have been shown to provide both a significantly improved understanding of important parameters governing residual stresses in pipe and vessel welds, as well as a unified scheme for achieving consistent residual stress prescriptions for supporting fitness-for-service assessments of engineering structures. Specific contributions of this investigation may be summarized as follows:

(a) A welding heating input characterization procedure has been developed and validated to relate prescribed temperature thermal modeling procedure to conventional linear input definition. With this development, a large number of parametric analyses can be carried in a cost-effective manner without relying on the heat flux based weld pool model that can be exhaustive and time-consuming.

(b) A set of governing parameters controlling important residual stress distribution characteristics regardless of joint types, materials, and welding procedures have been identified. These are characteristic heat input intensity and radius over thickness ratio.

(c) A shell theory based residual stress estimation scheme has been developed to interrelate all parametric analysis results for circumferential girth welds, which can also be used to estimate residual stress distributions in both through-thickness and at any distance away from the weld, for cases that are not covered in the parametric study.

(d) In a similar manner, a curve bar theory based residual stress estimation scheme has also been developed for longitudinal seam welds.

These developments can significantly advance the residual stress profile prescription methods stipulated in the current national and international FFS Codes and Standards such as 2007 API 579 RP/ASME FFS-1 and BS 7910: 2011.

Rights

The University of New Orleans and its agents retain the non-exclusive license to archive and make accessible this dissertation or thesis in whole or part in all forms of media, now or hereafter known. The author retains all other ownership rights to the copyright of the thesis or dissertation.

Available for download on Friday, December 15, 2017

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