The Electric Power Research Institute (EPRI) published a 2016 report on the use of laser peening to mitigate stress corrosion cracking (SCC) in nuclear reactors. Laser peening has been applied to critical welds in Japanese nuclear pressure vessels to mitigate SCC since the 1990s.
From the abstract: “During the past two decades, stress corrosion cracking (SCC) has become the most relevant phenomenon affecting nuclear plant availability and plant lifetime management. SCC can lead to increased costs for operation, maintenance, assessment, repair, and replacement of boiling water reactor (BWR) and pressurized water reactor (PWR) components.”
“The experimental results demonstrate that surface stress improvement (SSI) treatments are effective measures in preventing future initiation of primary water stress corrosion cracking. When properly applied, SSI treatments – converting residual stress status from tension to compressive to a certain depth – successfully eliminate the potential for future SCC initiation at surfaces exposed to reactor coolant.”
Laser peening provides service life extensions through enhanced fatigue strength and damage tolerance, along with resistance to corrosion, cracking, and fretting.
LSP Technologies’ Procudo® 200 Laser Peening System
LSP Technologies, Inc. (LSPT) announced the sale of its state-of-the-art Procudo® Laser Peening System to the Guangdong University of Technology (GDUT) in Guangzhou, China. The sale includes a 200-watt Procudo® 200 Laser Peening System along with paired work cell and robotic part manipulation equipment for a fully-integrated production-quality laser peening facility. The equipment will be delivered in early 2017, and installed on GDUT’s campus. GDUT will use the system to conduct research and application development on laser peening (LSP), laser peen forming, and laser-material interactions. This sale represents LSP Technologies’ introduction into the Asian material improvement market, and the equipment will provide GDUT with the fastest high-energy laser peening system currently available anywhere in the world.
Figure 1: Illustration of pilgering process courtesy of thefabricator.com
Cold pilgering is an important metalworking process for producing seamless pipes and tubes for critical high stress applications. The process involves feeding prefabricated tubes through rotating steel dies to reduce their diameter and wall thickness (Figure 1). Cold pilgering is applied to many different metals – steel, copper, titanium, etc. – and has applications across industries ranging from zirconium tubes in nuclear power plants, hydraulic tubes in aircraft, umbilical tubes for offshore oil platforms, and high-performance golf club shafts.
Pilger dies are subjected to cyclic loading at significant pressures (up to 1500 MPa for some alloys) and are thus prone to fatigue failures within the die grooves. When a pilger die begins to fail, small cracks are introduced into the forming groove surface requiring post-process sanding to remove the defect. These cracks will eventually grow to the point where tube defects can no longer be eliminated, forcing the die to be removed from service.
Residual stress modeling enables optimal surface enhancement for reducing high-cycle fatigue effects and improving component service life.
LSPT is developing an advanced modeling tool that integrates surface enhancement applications with fatigue failure rates.
LSP Technologies, Inc. (LSPT) is developing an analytical modeling tool for use in design and repair of engine hardware for the U.S. Naval Air Systems Command (NAVAIR). LSPT has been awarded Small Business Innovation Research (SBIR) Phase I funding to develop a probabilistic modeling tool that provides high-cycle-fatigue (HCF) failure rate prediction models relative to available surface enhancement treatments.
“Currently, there is no existing modeling tool with this level of probabilistic functionality,” explains Stan Bovid, Senior Materials Engineer at LSPT and Project Manager for the SBIR Phase I initiative. “We plan to develop and demonstrate an advanced software tool capable of incorporating residual stress profiles from different surface treatments into a probabilistic distribution of factors that contribute to fatigue failure.”
LSP Technologies is excited to be attending the upcoming Technology, Systems and Ships symposium in Arlington, Virginia. The event is hosted by the American Society of Naval Engineers, and highlights the latest efforts of the Navy, Coast Guard, Marine Corps, and Army to design and procure the next generation of weapons, systems and ships.
LSPT representatives David Lahrman and Doug Eberhart will occupy booth 221 February 15-16. The show includes exhibitors from major organizations across the maritime and shipbuilding industry, including: Huntington Ingalls Industries, General Dynamics Mission Systems, and the American Bureau of Shipping.
March 23, 2017 1-2 PM EDT
Subscribe to our next webinar for an in-depth look at how laser parameters are optimized to produce compressive residual stresses in materials. Learn about the relationship between power density, pulse width, and spot pattern, and how laser parameters are selected to generate compressive stress waves.
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Laser peening provides an important benefit over other metal enhancement methods when it comes to incident angle and stress wave propagation. As illustrated in Figure 1, the stress wave produced by laser peening always propagates perpendicular to the part surface, even when the beam impact angle is not perpendicular. This allows laser peening to be applied to parts with complex shapes or intricate geometries, while maximizing the achievable depth of compressive residual stresses within the part.
Figure 1: Illustrations of laser peening at different angles.