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Determining the Depth of Penetration During Submerged Arc Welding
Navy SBIR 2009.3 - Topic N093-210 NAVSEA - Mr. Dean Putnam - [email protected] Opens: August 24, 2009 - Closes: September 23, 2009 N093-210 TITLE: Determining the Depth of Penetration During Submerged Arc Welding TECHNOLOGY AREAS: Materials/Processes ACQUISITION PROGRAM: NAVSEA’s National Shipbuilding Research Program (NSRP) OBJECTIVE: The objective of the topic is to develop and implement new, innovative Submerged Arc Welding (SAW) technologies that can impact the cost and cycle time to construct, modernize, maintain and repair the Navy’s fleet. DESCRIPTION: SAW is a common welding method used in most of the automated, plate, butt-welding processes such as panel-line assemblies. Many plates are welded using SAW tractors and are welded from both sides to ensure full penetration and acceptable quality. When two-sided welding is required, it is performed in a multi-step process requiring significant material handling, back-gouging, and redundant welding. In simplified terms, a double-sided welded involves welding from one side, flipping the plate, and then completing the weld from the other side. Because most applications of SAW require full penetration, the key to double-sided welding is ensuring that the "backside" weld fully penetrates and fuses into the weld deposited on the first side. In most cases, full penetration is assured by back-gouging prior to welding of the second side (or backside weld). Back-gouging can be defined as the removal of base-metal as well as weld-metal from the side opposite of a partially welded joint to facilitate complete joint penetration. Back-gouging may be carried out by chipping, flame gouging, arc-air gouging, or grinding; with subsequent cleaning of the gouged area to ensure a clean, sound surface is available for depositing the second side weld. The depth and width of the back-gouged area is what is the minimum necessary to guarantee that the backside weld can be deposited against sound metal and can completely penetrate the weld root area. Thus, back-gouging generally requires removal of base metal as well as some (and often significant amounts) of the weld metal that was deposited from the first side. It follows, that elimination of back-gouging could significantly save time a cost through: (1) eliminating the steps associated with the back-gouging process and (2) reducing the volume of weld metal needed to complete the backside. This so-called, "no back-gouge" method is approved in limited cases. One major issue limiting the use of the "no back-gouge" method is the inability to reliably control penetration. If one could accurately control weld penetration from the two sides (e.g., ensuring 60% penetration from both sides), then one could extend the use of "no back-gouge" procedures to greater thicknesses. Similarly, for field connections in which SAW is used to weld the top side and overhead Flux-Cored Arc Welding (FCAW) is used to complete the second side, penetration control could maximize the amount of SAW without the chance from a blow through. Most structural butt joints require full penetration to pass non-destructive evaluation acceptance criteria (MIL STD 2035A) and to ensure adequate performance. Currently, there is no effective in-process method of determining depth of penetration. Thus, for double-side weld applications, the costly back-gouge method is used. As the submerged arc process does not permit the welder to observe the welding process (due to the cover layer of flux), it is not possible for the welder to monitor the weld pool to visually determine weld quality. The two primary methods of non-destructive testing used to ensure adequate weld penetration in double-sided welds are ultrasonic testing and radiography; neither method can be used while welding is in process. This topic seeks to develop the methodologies and associated enabling technologies to accurately control the depth of weld penetration during the SAW process. This capability, especially if performed in real-time, could expand the currently used "no back-gouge" method beyond the today’s limits, significantly increasing cost savings. In-process weld monitoring will also reduce the iterative process required to determine the initial welding parameters for new applications. The largest technical challenge of this topic is developing a weld-depth monitoring method and equipment that can overcome the lack of weld pool visibility inherent in the SAW process. Therefore, an innovative, potentially high-risk solution is required. A successful, in-process SAW penetration-monitoring technology will have a tight penetration tolerance, must be capable of monitoring varying weld gaps due to fit up variations, must produce welds capable of meeting the requirements of MIL-STD-2035A, and will maintain or increase shipyard throughput on the panel welding line. The system will also need to be ruggedized to meet the harsh shipyard environments including resistance to high temperatures and weld splatter. The innovative solutions must be compatible with current shipyard practices and processes. This topic also seeks innovative scientific and engineering solutions to inefficiencies in long-standing ship construction processes. This topic offers an opportunity to infuse new ideas and innovations into the domestic shipbuilding industry. Of particular interest are initiatives with a clear business case. Proposals should specifically describe the technology that will be applied to solve the problem, how it will be developed, what the estimated benefits will be and how it might be transitioned into the shipbuilding industry. National Shipbuilding Research Program (NSRP) members are available to provide guidance and assistance in the identification of common issues and needs. Contact with these resources is encouraged both prior to proposal development and during any subsequent SBIR-related activity. Teaming with a NSRP member is voluntary and will not be a factor in proposal selection. PHASE I: Demonstrate the feasibility of an in-process method of accurately controlling and monitoring the depth of weld penetration during the SAW process. Demonstrate improvements being developed and also identify impact upon shipbuilding affordability. Include a first order Return-On-Investment (ROI) analysis for industry implementation and estimate potential Total Ownership Cost (TOC) reduction. Establish Phase II performance goals and key developmental milestones. PHASE II: Finalize the Phase I design and demonstrate a working prototype of the proposed system. Perform a demonstration to validate the performance characteristics established in Phase I. A demonstration in a representative (i.e., shipyard) environment is preferred; however, a laboratory demonstration is acceptable if steps are taken to incorporate critical characteristics of the shipyard environment. Develop a detailed plan and method of implementation into a full-scale application within the US Shipbuilding and Repair Industry. PHASE III: Implement the Phase III plan developed in Phase II in coordination with the Shipbuilding and Repair industry. PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: The technology developed under this topic shall be directly applicable to current military and commercial shipbuilding operation and repair practices. The products developed should find wide use in most heavy industrial plant/processing facilities such as the power or offshore oil industries and will be marketable to the shipbuilding and repair industry. REFERENCES: 2. US Naval Shipyard information is available at http://www.shipyards.navy.mil 3. http://en.wikipedia.org/wiki/Submerged_arc_welding 4. MIL-STD-2035A, Nondestructive Testing Acceptance Criteria KEYWORDS: Welding; SAW; NDT; NSRP; Butt Welding; Monitor
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