Electronic Theses and Dissertations

Identifier

595

Date

2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Mechanical Engineering

Concentration

Mechanical Engineering

Committee Chair

Gary Qi

Committee Member

John I Hochstein

Committee Member

Hsiang H Lin

Committee Member

Tommy L Jamison

Abstract

Stout, Charles Anthony. PhD. The University of Memphis. May 2012. Evaluation of the Relationship Between Tensile Strength and Hoop Strain in C122 Copper Tube and Fittings. Major Professor: Dr. Gary QiCurrent methods of calculating the operating and burst pressures of C122 copper piping systems do not adequately predict performance. This is due to the fact that most equations used in pressure piping were developed using steel which has a clearly defined elastic region of its stress-strain curve. Annealed copper does not have a well-defined elastic deformation region in the stress-strain curve. The disconnect between calculated performance and observed performance has led to an environment where engineers have made design changes not fully understanding the resulting effect on performance to the customer. Over design costs manufacturers in the form of material costs and under design may give the customer products that fail prematurely.The purpose of this study was to relate measured hoop strain, which has been shown in previous studies to be a good predictor of performance, in annealed C122 copper to some of the performance criteria found in ASME, ASTM, and other consensus standards. This allows for the continued use of the current performance criteria. The approach of relating hoop strain to standard performance criteria has two key benefits: first, it allows for the use of terms that the industry is already accustomed to using and second, it will allow for an accurate test that can be done quickly for acceptance of product. This study was accomplished by conducting hoop strain, tensile strain, grain size determination, and hardness tests on the products of eight different manufacturers of copper tube and fittings. The diversity in manufacturers was used to assure that the results were applicable for the copper industry. The data resulting from the testing was analyzed using JMP 9 to determine the best model for predicting 1% hoop strain pressure in copper tube and fittings. Hoop strain is defined as the change in outer diameter of the tube divided by the original tube diameter. 1% hoop strain was selected during screening testing due to concerns of whether extremely large straining of piping would be unacceptable due to difficulty with repair.Evaluation led to the selection of a linear relationship between burst pressure and 1% hoop strain pressure. The relationship showed that 1% hoop strain pressure can be predicted if burst pressure is multiplied by 0.35. This relationship has an R Square value of 0.851, which may be accurate enough for acceptance as a reasonable predictor for the codes bodies. Low purity C122 copper will burst at a lower pressure than higher purity C122 copper, which leads to lower strain prediction than actually observed. This penalty is acceptable as three times burst pressure is an existing criterion seen in some of the third party verification agencies currently. This methodology can be implemented within the consensus standards until a more robust model can be found.

Comments

Data is provided by the student.

Library Comment

Dissertation or thesis originally submitted to the local University of Memphis Electronic Theses & dissertation (ETD) Repository.

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