ASME Pressure Vessels & Piping Conference

June 10, 2019

Join us in San Antonio, Texas for the ASME Pressure Vessels & Piping Conference (PVP). The ASME 2019 PVP Conference is an exceptional international technical forum for participants to further their knowledge by being exposed to diverse topics, and exchange opinions and ideas both from industry and academia related to Pressure Vessel and Piping technologies for the Power and Process Industries.

When:  July 14-19
Where: Hyatt Regency San Antonio Riverwalk in San Antonio Texas

Intertek engineering experts will be presenting:

Further Improvements to ASME Section XI Code Case N-806 in a Proposed Second Revision
(N-806 provides guidance for flaw evaluation in degraded buried pipe)

The Code Case addresses the nuclear industry need for evaluation procedures and acceptance criteria for the disposition of metal loss that is discovered during the inspection of metallic piping buried in a back-filled trench. In a second revision of the Code Case, several changes are proposed. First, guidance is provided for analytical evaluation of greater detail including finite element analysis methods. A new non-mandatory appendix is included to provide procedures for the evaluation of soil and surcharge loads using finite element analysis. Next, a second new non-mandatory appendix is provided giving detailed guidance on the evaluation of seismic loads. Finally, the need to evaluate the fatigue life of buried piping subjected to cyclic surface loading is now included and a design factor applied to the modulus of soil reaction is introduced. This paper presents details of the proposed changes to Code Case N-806-1 and their technical basis where applicable.

Application Examples of ASME Code Case N-513 Implementation
(N-513 provides guidance for temporary acceptance of leaking moderate energy piping)

This paper provides three application examples of the Code Case implementation based on US plant operating experience. Specifically, detailed evaluations of through-wall leakage in straight pipe, a piping elbow and gate valve body are provided. These examples will help facilitate Code Case employment by future users.

Creep Life Evaluations of ASME B31.1 Allowance for Variation from Normal Operation – 11 Materials 

The ASME B31.1-2018 Power Piping Code (Code) paras. 102.2.4, 102.3.3, and 104.8.2 provide an allowance regarding operating above the design temperature and design pressure for short time periods. The concept of allowing occasional operation for short periods of time at higher than the design pressure or design temperature has been in the Code since 1967. These 1967 Code para. 102.2.4 limitations were based on engineering judgment that can now be quantitatively evaluated for the additional creep life consumption (creep rupture damage accumulation). This study primarily is a quantitative estimate of the permitted increased life consumption, considering minimum creep rupture properties, associated with the 2018 Code operating allowances for piping materials operating in the creep range. Eleven base metal materials are considered in this paper – low carbon steel, 1.25Cr 0.5Mo, 2.25Cr 1Mo, 9Cr 1 Mo V, Type 304 SS, Type 316 SS, Type 316L SS, Type 321 SS, Type 321H SS, Type 347 SS, and Type 347H SS.

Power Piping Grade 91 In-service Cracks

This paper considers historical early service-related cracks in weldments of power piping systems operating in the creep regime. Factors that dominate these early service-related cracks are discussed in this paper. This paper provides a list of more than 20 historical examples of power piping Grade 91 material macrocracks (partial wall or through-wall) that were not present immediately after construction and propagated substantially in service. Five of the examples are discussed in more detail. The study only includes cases where propagating cracks were confirmed. It does not include examples where NDE reportable indications have not propagated in service to large macrocracks. Due to the time-dependent nature of these girth weld cracks, the results of this study may be used to assist in the selection of Grade 91 re-examination locations after the power piping system (e.g., main steam, hot reheat, high pressure, or intermediate pressure) has been several years in service.

Large Ranges in Power Piping Girth Weld Creep Rupture Lives

Over the past 20 years, the authors have evaluated several hundred piping systems operating in the creep range, including main steam, hot reheat, high pressure, and intermediate pressure systems constructed of Grade 11 (1¼-Cr-½Mo-Si), Grade 22 (2¼Cr-1Mo), and Grade 91 (9Cr-1Mo-V) materials. Stress contour plots illustrate the significant range of Code stresses (sometimes factors greater than 2) at various piping system locations. This study also considered the variation of high stress locations for the initial as-designed piping stress analysis versus the as-found stresses associated with field anomalies. The stress contour plots also illustrate that field anomalies in sister units can result in different high stress locations from one unit to another. In addition, significant unintended field anomalies may result in as-found analysis high stress locations at low stress as-designed (expected) analysis locations. Since there is a large range of stresses in these power piping systems, the girth welds have a significant range of creep rupture lives. In Grade 11 material operating at 1000°F (538°C), an 18% stress increase results in 50% decrease in creep rupture life. In Grade 22 material operating at 1000°F, a 12% stress increase results in 50% decrease in creep rupture life. In Grade 91 material operating at 1060°F (571°C), an 8% stress increase results in 50% decrease in creep rupture life. For Grades 11, 22, and 91, the creep rupture times are a function of stress to the powers of 4, 6, and 9, respectively. Consequently, the evaluation of the large range of stresses in these piping systems revealed that the piping system girth welds can have creep rupture lives varying by more than a factor of 10. The large range of piping stresses and associated large range in creep rupture lives within a piping system are illustrated as stress histograms for several example piping systems. Four case studies illustrate successful selection of girth weldments with the most in-service related creep damage.

Application Examples of ASME Code Case N-513 Implementation

Code Case N-513 provides evaluation rules and criteria for temporary acceptance of flaws, including through-wall flaws, in moderate energy piping. The application of the Code Case is restricted to Class 2 and 3 systems, so that safety issues regarding short-term system operation are minimized. The first version of the Code Case was published in 2000. Since then, there have been five revisions to the Code Case that have been published by ASME. The Code Case has been used numerous times by utilities to avoid unscheduled shutdowns without impacting plant safety. Recent revisions of Code Case N-513 continue to expand its scope to piping components including elbows, reducers, branch tees and gate valve bodies. This paper provides three application examples of the Code Case implementation based on US plant operating experience. Specifically, detailed evaluations of through-wall leakage in straight pipe, a piping elbow and gate valve body are provided. These examples will help facilitate Code Case employment by future users.

Effect of Bending Load on Burst Pressure of Nuclear Power Plant Steam Generator Tubes with Uniform Wall Thinning

Tube integrity is an important aspect for safe and reliable operation of nuclear power plant steam generators. As a licensing requirement, all in-service steam generator tubes shall retain structural integrity over the full range of normal operating conditions and design basis accidents by meeting the structural integrity performance criterion. The burst strength of tubes subjected to wall thinning will depend on the extent and mode of degradation, and the magnitude of design loads to include pressure differential across the tube wall during normal operation and postulated accident conditions. In addition, non-pressure loads that can occur during postulated accident events shall be evaluated and included in the assessment of tube integrity if determined to significantly reduce the tube burst strength. 

The EPRI Flaw Handbook provides burst pressure relationships for flaws which include a pressure reduction factor that accounts for the effect of applied bending stress on tube burst. However, this previous industry work was only for planar crack-like flaws and did not directly address uniform volumetric wall loss.  This paper describes a test program to determine the effect of bending loads on the burst pressure of a tube with uniform thinning over a given axial length.  The uniform thinning geometry was selected since it represents a bounding case of general wall loss and is conservative. The tests results show that addition of a bending stress in the burst testing of a thinned tube caused the onset of plastic straining with measurable strain hardening but no apparent reduction in the burst strength under internal pressure. This determination was reached by comparing the burst pressure of tubes with similar flaws with and without an applied bending load. These test data will aid in modifying the burst models if the effects of bending load are to be included for volumetric degradation.

About the speakers: 


Marvin Cohn- Mechanical Engineer, P.E., P.Eng., FASME

Marvin Cohn has over 35 years of experience in the fields of engineering mechanics, stress analysis and metallurgy. He graduated with a B.S. in Physical Metallurgy from the University of Washington and obtained an M.S. in Engineering from the University of California. Marvin is an author of more than 50 technical papers, including eight professional journal papers, and is a member of the American Society of Mechanical Engineers (ASME) as well as a member of the ASME B31.1 Power Piping Section Committee.

His recent work involves simulation of high energy piping calculated displacements to field measurements for more accurate stress predictions and remaining creep life estimates of main steam and hot reheat piping systems.  Marvin has provided litigation support for disputes involving the contracted design of high energy steam piping. 

Russ Cipolla, P.E. – Principal Engineer

Mr. Cipolla has experience with advanced applications of fracture mechanics; remaining life prediction methods; ductile fracture of metals; integrity of structures containing flaws; and fitness-for-purpose analysis. Expertise in finite element and singular integral equations analysis techniques; elastic-plastic and fully plastic analysis methods; transient heat transfer and thermal stress analysis; American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code Section III and Section XI.

Bob McGill, P.E. – Principal Engineer

Mr. McGill specializes in fitness-for-service evaluations of ASME Section III and B31.1 nuclear piping and components. He is an active member in several ASME Section XI committees focused on Code Case development to support piping integrity assessments. In addition, Mr. McGill is a leading consultant for the thermal fatigue management program sponsored by EPRI since 2005. His involvement has included development of guidance reports and supporting stress, fatigue and fracture mechanics analyses. He has conducted dozens of EPRI sponsored training sessions for industry engineers related to thermal fatigue. Mr. McGill has over 15 years of engineering consulting experience within the nuclear industry.