Overlay Repair Research Articles

Management of the keel nose and associated valve collapse.

To analyze the anatomical abnormality of the keel nose and correlate the findings with etiologic maneuvers of a routine rhinoplasty procedure; to identify the contributing factors and offer suggestions to avoid or decrease the severity of these surgical complications; and to present an effective revisional procedure to correct the functional and cosmetic consequences of this deformity. A total of 47 patients (31 women and 16 men; age range, 18-71 years) with a keel-appearing nose presented for revision rhinoplasty. All had undergone at least 1 rhinoplasty procedure, and 39 had undergone 2 or more previous nasal procedures. All patients had bilateral lateral nasal wall collapse and an associated severely compromised internal nasal valve. All patients underwent reconstruction with a conchal cartilage overlay graft. All patients had a moderate to excellent cosmetic improvement; the subjective improvement in nasal airway was more dramatic. Since patients with a keel nose have an associated internal valve collapse, both abnormalities are addressed simultaneously with the conchal cartilage overlay repair, which results in minimal morbidity with no major complications. Conchal cartilage overlay repair uses a cartilage graft from the auricle with a recommended external rhinoplasty for placement. Appropriate sizing and fashioning precede the precise placement and suture fixation. This technique addresses both functional and cosmetic abnormalities.

Residual Stress Measurement in 304 Stainless Steel Weld Overlay Pipes

Welding overlay repair (WOR) is commonly employed to rebuild piping systems suffering from intergranular stress corrosion cracking (IGSCC). To understand the effects of this repair, it is necessary to investigate the distribution of residual stresses in the welded pipe. The overlay welding technique must induce compressive residual stress at the inner surface of the welded pipe to prevent of IGSCC. To understand the bulk residual stress distribution, the stress profile as a function of location within wall is examined. In this study the full destructive residual stress measurement technique—a cutting and sectioning method—is used to determine the residual stress distribution. The sample is type 304 stainless steel weld overlay pipe with an outside diameter of 267 mm. A pipe segment is cut from the circular pipe; then a thin layer is removed axially from the inner to the outer surfaces until further sectioning is impractical. The total residual stress is calculated by adding the stress relieved by cutting the section away to the stress relieved by axially sectioning. The axial and hoop residual stresses are compressive at the inner surface of the weld overlay pipe. Compressive stress exists not only at the surface but is also distributed over most of the pipe’s cross section. On the one hand, the maximum compressive hoop residual stress appears at the pipe’s inner surface. The magnitude approaches the yield strength of the material; the compressive stress exists from the inner surface out to 7.6 mm (0.3 in.) radially. On the other hand, compressive axial residual stress begins at depths greater than 2.5 mm (0.1 in.); its maximum value is located at 10.7 mm (0.42 in.) with magnitude close to four-tenths of yield strength. The thermal-mechanical induced crack closure from significant compressive residual stress is discussed. This crack closure can thus prevent IGSCC very effectively.

Measurement of residual stress in the weld overlay piping components

In general industry, especially in the nuclear industry, welding overlay repair is an important repair method mainly used to rebuild piping systems suffering from intergranular stress-corrosion cracking (IGSCC).

Measurement and simulation of residual stress in type 304 weld overlay stainless steel pipe

Repair by welding overlay is a commonly used method mainly employed to rebuild piping systems suffering from intergranular stress corrosion cracking (IGSCC). It is desirable that the overlay welding technique, by attaching an overlay weld to the pipe and sustaining a heat sink of flowing water inside the pipe, induces a compressive residual stress at the inner surface of the welded pipe for prevention of IGSCC. A better understanding of the effect of a welding overlay repair on the residual stresses at the inner and outer surfaces of weld overlay is thus required. To obtain this understanding, it is necessary to investigate the distribution of residual stresses on the welded pipe. In this study, the hole-drilling strain-gauge method was adopted to determine the residual stresses at the inner and outer surfaces of the weld overlay pipe. The incremental drilling technique was used on pipes with outside diameters of 267 mm. In addition, the Weld 3 code was applied to simulate the residual stress distribution for comparison and verification with the measured results. The results obtained from the experimental and from the computational methods are in good agreement. The residual stress at the inner surface of the pipe is compressive with a magnitude approaching the yield stress of the material; that at the outer surface is tensile, also with a magnitude close to yield stress but smaller than the compressive stress. The experimental residual stress magnitude is generally greater than that from computation. This observation can be attributed to several factors including applied mechanics, temperature distribution, original residual stress, strain gauge location, mechanical grinding and the oxidation layer.

Weld overlay repairs from conception to long-term qualification

The weld overlay was initially developed in 1982 as an interim repair for intergranular stress corrosion cracking (IGSCC) flawed welds in boiling water reactor stainless steel piping. Since that time extensive work has been performed to qualify the weld overlay repair technique for longer-term service. Analytical studies of the weld overlay process, experimental programs on laboratory and field specimens, tests to demonstrate the beneficial effects of the weld overlay over its service life, and programs to develop nondestructive examination (NDE) techniques for use in inspecting weld overlays have all yielded positive results. These programs have been sponsored by the utility industry, either individually, through EPRI sponsorship or as part of the BWR Owners' Group (BWROG) effort, and by the US Nuclear Regulatory Commission (USNRC). Weld overlay repairs serve several design functions. These include: structurally reinforcing the flawed location to restore code margins to failure, providing an IGSCC-resistant barrier to crack growth, and imposing a favorable residual stress distribution in the inner portion of the flawed component to inhibit further flaw initiation and growth. The qualification programs confirm that these design functions are maintained with long-term service. A regulatory barrier to long-term operation with weld overlays was the need periodically to inspect overlays and thereby demonstrate continued integrity. Although IGSCC flaws have generally been detected by ultrasonic methods, the repair of these flaws by weld overlay made continued monitoring of the repaired flaw by conventional ultrasonic techniques difficult. Recent developments in ultrasonic examination equipment and techniques, including surface preparation criteria, have enhanced the inspectability of weld overlay repairs and the underlying base material. The original acceptance of weld overlay repairs by the USNRC was for limited service (one or two fuel cycles of operation). However, more recent regulatory guidance, including the recently issued NUREG-0313, Revision 2, recognizes the above technical advances, and provides criteria for acceptance of weld overlays as long-term repairs. Several US utilities have been successful to date in obtaining USNRC approval for extended operation with weld overlays. Some overlays at these plants are currently entering their fourth successful fuel cycle of operation.

Weld overlay of BWR flawed piping

The occurrence of intergranular stress corrosion cracking (IGSCC) in the reactor water clean-up (RWCU) system and the recirculation systems in Boiling Water Reactors (BWR) has plagued utilities in the United States over the past few years. There are those who believe that if significant IGSCC exists, the only long-term solution is to replace the affected piping. Nevertheless, there are also those who contend that if only moderate flaws exist, the application of induction heating stress improvement (IHSI) and/or the installation of a hydrogen injection system may provide for a long-term solution to the problem. In the meantime, flawed pipes have been repaired with a weld overlay procedure to allow utilities the necessary time to plan and prepare for a permanent resolution. This paper describes the evolution of weld overlay repair designs and suggests that if the obstacle of inspectability can be overcome, it may be possible to consider the weld overlays themselves as the long-term solution.