Shane J. Findlan

Weld repair of steam turbine casings and piping: An industry survey

As the U.S. fleet of fossil power plants age, utilities are forced to perform more and more repairs on such components as turbine casings, main and reheat piping, headers, and other components that have experienced high-temperature degradation. This paper presents information from two surveys on the weld repair technologies currently used by utilities and repair organizations to extend the life of high-temperature, high-pressure components. The initial survey included responses from 28 EPRI member utilities on various repair issues ranging from condition assessment to preheat/postweld heat treat to filler metals employed. The second survey was forwarded to repair vendors and OEMs to gain their perspective on utility industry repairs.

Performance of Repair Welds on Service-Aged 2-1/4Cr-1Mo Girth Weldments

This paper discusses the results of evaluations performed on service-aged piping using both conventional postweld heat treatments and temperbead repair techniques. The two repair weldments were accomplished on two 2-1/4Cr-1Mo pipe girth weldments which were removed from a utility hot reheat piping system in the fall of 1992 after 161,000 h of operation at 1,000 F (538 C). Each repair was performed around one-half of the diameter of a pipe girth weldment, while the remaining half of the girth weldment was left in the service-aged condition. Post-repair metallurgical and mechanical test results indicated that both weld repairs produced improved remaining lives when compared to the service-aged girth weldments. Since the two ex-service weldments that were utilized in weld repairs exhibited different stress rupture strengths to start with, the performance of temper bead and postweld heat-treated (PWHT) repair could not be compared directly. It was clear, however, that life extension periods exceeding 30 yr could be achieved by temperbead repairs, with improved toughness and with no loss of stress rupture ductility, tensile strength, or yield strength. The temperbead repair improved the toughness of the service-aged weldment, while the postweld heat-treated repair lowered the HAZ toughness.

Weld repair of 2-1/4Cr-1Mo service-aged header welds

The objective of this investigation was to evaluate the efficacy of different weld repair techniques as applied to service-aged 2-1/4Cr-1Mo steel weldments. A header which had been in service for 244,000 h at 1,050 F (565 C) was utilized for the study. Three girth welds were partially excavated and subjected to repairs using gas tungsten arc welding (GTAW), shielded metal arc welding (SMAW) with postweld heat treatment (PWHT), and without postweld heat treatment using a temperbead technique. Results show that all the weld repairs improved the creep rupture lives of the ex-service weldments and that remaining lives of several decades could be achieved in the repaired condition. The SMAW-temperbead repairs resulted in increase of future life, tensile strength, and impact toughness compared to the SMAW-PWHT repairs. The GTAW-PWHT repairs also produced a superior combination of mechanical properties. Remaining creep rupture lives were a function of the extrapolation procedure and specimen size. These results are described here and discussed in comparison with results previously reported for a less severely degraded condition of the steel in order to delineate the effect of prior degradation on weld repair performance.

Tensile Testing and Material Property Development of High Density Polyethylene Pipe Materials

Degradation of service water systems is a major issue facing nuclear power plant owners, and many plants will require repair or replacement of existing carbon steel piping components. High Density Polyethylene pipe has been used in non-safety service water systems for over nine years and found to perform well, but it is not currently permitted in the ASME Section III Boiler and Pressure Vessel Code, Division 1 for use in nuclear safety-related systems. To assist in the implementation of High Density Polyethylene pipe in the ASME Boiler and Pressure Vessel Code, Section III, Division 1 for Safety Class 3 applications, EPRI initiated a High Density Polyethylene pipe and pipe material testing program. This test program includes tensile testing and fatigue testing of High Density Polyethylene piping and piping components and the development of slow crack growth data. To determine the material and engineering properties needed, extensive tensile testing of specimens cut from High Density Polyethylene pipe was conducted. The initial tensile test program was conducted on PE 3408 with cell classification 345464C and a second, not yet finalized, phase was added to test PE 4710 with cell classification 445474C. The data developed during the testing were used to establish ultimate strain, elastic moduli, yield stress and yield strain values for both new and aged materials. Because extruded HDPE properties vary in the hoop and axial directions and the properties are highly affected by temperature, specimens were cut in both the hoop and axial directions and were tested at temperatures ranging from 50° F to 180° F. This paper provides a description and overview of the PE 3408 cell class 345464C test program. In addition, an overview and summary of the test results for the PE 3408 cell class 345464C are provided.Copyright

Bending Fatigue Testing of Pipe and Piping Components Fabricated From High Density Polyethylene Materials

Degradation of service water systems is a major issue facing nuclear power plant owners, and many plants will require repair or replacement of existing carbon steel piping components. High Density Polyethylene pipe has been used in non-safety service water systems for over nine years and found to perform well, but it is not currently permitted in the ASME Section III Boiler and Pressure Vessel Code, Division 1 for use in nuclear safety-related systems. To assist in the implementation of High Density Polyethylene pipe in the ASME Boiler and Pressure Vessel Code, Section III, Division 1 for Safety Class 3 applications, EPRI initiated a testing program that includes tensile and fatigue testing of HDPE piping and components and the development of slow crack growth data. Straight cantilever bending fatigue tests on PE 4710 pipe with a minimum cell classification of 445474C were conducted. The tests were designed to comply with the requirements for fatigue testing given in Appendix II of the ASME Boiler and Pressure Vessel Code, Section III, Division 1. They were also designed to achieve failure at the fusion butt welds near the cantilever support. S-N curves developed from both sets of data were found to fit well to power formulas of the type S = C/Nb required by mandatory Appendix II. The tests were conducted at various temperatures from 50° F to 160° F and in addition the effects of cyclic rate and aging were evaluated. Based on the straight pipe tests, stress intensification factors were calculated for 5-segment miter bends in both the in-plane and out-of-plane directions. The test elbows were fabricated from PE 4710 material with cell classification 445474C. Two sizes of 5-segment miter bends were tested, 4” and 12” diameter. The fatigue testing results showed one of the unique characteristics of High Density Polyethylene pipe: a significant decrease in material stiffness from the first few test cycles to a lower value that remains almost constant until failure. Thus, S-N curves and SIFs were determined twice: first based on the initial cycle results and again at the midlife of the fatigue tests. This paper provides a description and overview of the test program, testing methods and materials tested. In addition, an overview and summary of the test program results are provided.© 2008 ASME

External Weld Overlays for Repair of Pressure Components

External weld metal deposit overlays have been successfully implemented in industry as both temporary and permanent repair for the restoration of thinning or degraded steel piping. Pressure components systems suffer from numerous degradation mechanisms, including microbiologically influenced corrosion (MIC), erosion-corrosion damage (EC), fatigue, and general corrosion. The magnitude of the damage induced in the component determines whether a weld overlay repair can be successfully applied to restore the component’s integrity. This paper addresses the use of weld overlays for repair of pressure components degraded by wall thinning due to corrosion, erosion-corrosion, MIC and other mechanisms.Copyright