Argon Arc Welding for Pipelines
Improvement of Methods of Automatic Self-Compression Argon Arc Welding for Pipelines
Tech Area / Field
- MAN-MPS/Manufacturing, Planning, Processing and Control/Manufacturing Technology
- MAN-MAT/Engineering Materials/Manufacturing Technology
- OTH-BIT/Building Industry Technology/Other
3 Approved without Funding
NIKIMT (Institute of Assembly Technology), Russia, Moscow
- NPO Technomash, Russia, Moscow
- AREVA / Areva NP GmbH, Germany, Erlangen\nOtto-von-Guericke-Universität Magdeburg, Germany, Magdeburg
Project summaryDevelopment of industry and building of such facilities as nuclear and heat power plants, chemical, oil-treatment and gas enterprises, other facilities require application of HT processes and equipment for pipes welding. Building of such facilities demands tremendous scope of works for pipes welding. For example: by building of chemical plants over 80 thousand joints must be welded, heat-supply plants: up to 150 thousand joints; VVER type RPV: about 100 thousand joints. Main scope of works (up to 80%) relates to butts of pipelines with 8 – 76 mm O.D. In this case, the main requirement to pipelines is assurance of their service reliability and safety, which are significantly depending on quality of welds. Besides that, economical matters require high productivity of welding processes, what can be ensured by using of automated welding equipment and optimal technologies.
The programs of many world-famous firms: ESAB (Sweden), Arc Machines (USA), Polysoude (France), RTA (Italy), etc., provide development of technologies and manufacture of equipment for automated welding. In Russia NIKIMT, Technomash, Rzhev Mashzavod, etc perform such works at present time. Research and engineering development of pipelines welding is realized by mean of automation, development and selection of rational welding methods. Available experience shows great advantages of TIG welding process without filler wire regarding automation, development of pipe-welding equipment and quality assurance of welds. It is suitable especially to pipes with 3,5 – 4 mm wall thickness and 8 – 76 mm diameter.
However, a single-bead welding process without filler material does not allow produce strength reinforced seams because of thinning of their cross-section, especially for vertical orbital butt joins of pipes with wall thickness and diameter specified above. Available welding machines providing filler wire have great sizes and are in lower demand especially for mounting procedures.
These problems were successfully solved in Russia, where a principally new welding method was developed with use of self-compressing of welding seam. The method is featured by application of thermal-plastic deformations for forming of reinforced seam. Such deformations are caused in a welding joint by compressing stresses in welding area as result of irregular heating of butt joint by welding arc. In process of additional “compressing” passes performed by arc with lower energy input, simultaneously with transversal deformation of joint, a flow of heated metal occurs in radial direction and forming, as result of this, of two-side reinforcement of welding seam.
Besides that, early 70th a new version of self-compressing welding was developed: consequential penetration welding process. Applications of this process allowed make a significantly more simple technology without re-programming or reset of welding regimes when performing of “welding” and “self-compressing” passes. Some other analogue welding methods were also developed, for example: “anti-compressing”-, multi-bead processes and application of butt machining to avoid its transversal deformation.
However, until the present time no physical, material-study and technological features are not practically investigated regarding the self-compressing method, as well as no optimal technologies are developed for welding of several metals and alloys; not enough researches were performed for pipes with 4 –5 mm wall thickness, for properties and corrosion resistance of welds depending on heat input by welding, for consequence of welding passes, for service conditions; actual application areas of welding methods are not defined. There is no theoretical background for reinforcement forming mechanism, improvement of corrosion resistance and suppress of crack-building behavior by the self-compressing welding. The project of research works and development of new advanced kinds of this method is proposed, in order to ensure wide application in several industries of the method, which is economic, requires no complex equipment and high-skilled operators, ensures stable quality of welds.
Basing on this, the goal of this project is development of technological backgrounds for pipes welding by the self-compressing method and its application for automated welding of pipelines of several purposes.
The proposed project includes the following milestones:
- Analysis of available processes of automated pipe welding with use of the self-compressing method.
- Development and testing of new self-compressing welding processes for pipes made of several metals and alloys (corrosion-resistant-, chrome- and perlite steels, Fe-Ni alloys, nickel, copper and their alloys, titanium and its alloys, aluminum and its alloys).
- Study of welds properties:
- Strength, plasticity, impact strength;
- Resistance against inter-crystalline corrosion and corrosion in acid solutions;
- Metal-graph analysis of welding joints;
- Quality inspection of welding joints;
- Technological strength.
- micro-roentgen structural analysis and metal-graph with use of electronic- and optical microscopy;
- inter-crystalline corrosion testing of welding joints according to ISO 3651-1998 Standard;
- quality inspection of welding joints by Roentgen- and capillary flaw detection.
Research results and wide testing of advanced processes will allow optimize processes to be developed and issue necessary engineering documentation. Basing on research and testing results to be obtained, technological recommendations will be issued, which will allow wide application of the self-compressing method for automated welding in several building- and mounting industries.
Available experience of the project’s participants makes sure, that the project will be implemented in full scope, in proper time and on high scientific level. The project meets entirely the ISTC goals in involvement of weapon scientists in solving of quite civil tasks.