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Thermal Spraying In Wet Environment
Ohliger, A. (GKSS Research Centre) | Szelagowski, P. (GKSS Research Centre)
Offshore structures, especially in the North sea, are severely attacked by corrosion. Every year millions of dollars are lost by corrosion of unprotected areas of offshore structures and marine buildings. This is a fact which demands strong efforts on corrosion prevention especially as the availability of raw material runs shorter and shorter all over the world. Therefore a high demand on long lasting, on site applicable lifetime extending corrosion protection systems is growing intensively and high efforts are made to meet this challenge. Longterm protection is to be applied and maintained in situ offshore and it must be environmental tolerable. State of the art Offshore structures and marine buildings can be subde-vided into those parts which are normally always exposed to atmospheric air and submerged in the water. In between these two zones we find the splash zone (fig. 1). The first two of the above mentioned areas create more or less known demands to the corrosion protection systems as the type of aggression of the air or the water is always the same and does not differ throughout a long period. Some demands on the corrosion protection systems can more or less be met by the existing solutions (e.g. painting in air atmosphere or cathodic protection in sub- merged areas). The splash zone creates problems which are more serious as the structure can neither be protected perfectly by paint nor by any type (active or passive) of cathodic protection. For example the attack of waves, the collision with ship hulls, ice motion and the chemical attack of the sea water as well as the periodical immersion by tides and waves and the updrying of the surface by sun exposure create a severe aggression to the coating system. Unprotected areas or spaces of distortion of the coating are intensively exposed to oxidation and generation of rust.
- North America > United States (0.29)
- Europe > United Kingdom > North Sea (0.24)
- Europe > Norway > North Sea (0.24)
- (3 more...)
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)
Introduction The wet welding process has so far been applied to offshore structures and for pipeline repair in the Gulf of Mexico and other areas of the world, where lower strength steels (usually with a carbon equivalent below 0.37%) are used [1]. Higher strength steels traditionally used in the North Sea (with a carbon equivalent exceeding 0,40%) are generally thought to be unsuitable for wet welding, because of their susceptibility to hydrogen induced cold cracking, associated with high hardness, low toughness and low ductility [2/3/4]. Nevertheless, the wet welding process has recently been employed in the North Sea for a structural repair on a platform in summer 1990. The repair consisted of replacing a 30" diameter diagonal brace member with a scallop fillet sleeve wet weld at 10 metres water depths and by a conventional pup butt tie-in for the atmospheric welds [5]. Wet welding procedures for Type B groove and fillet welds were qualified in accordance with AWS-D3.6–83 specification using a ferritic type of electrode. The qualifications were carried out in high strength steel, BS 4360 Grade 500 as commonly used in North Sea structural components, having a carbon equivalent (CE) of 0,42%. The repair work has been successfully carried out by an internationally well known European diving company, which has demonstrated the wet welding process to be on its way of becoming a viable alternative for North Sea platform repairs.[6] However, this repair has been carried out at shallow water depth only, so that there is still the need to develop the necessary wet welding technology (consumables, equipment, procedures etc.) required for greater water depths. Stale of the Art The advantage of the application of the Shielded Metal Arc Welding (SMAW) technique directly in water is characterized by:–elimination of special purpose habitat –rapid mobilization
- North America > United States (1.00)
- Europe > United Kingdom > North Sea (0.86)
- Europe > Norway > North Sea (0.86)
- (3 more...)
Automatic And Diverless Underwater Welding: New Systems And Concepts
Dos Santos, J.F. (GKSS-Forschungszentrum Geesthacht GmbH) | Manzenrieder, H. (GKSS-Forschungszentrum Geesthacht GmbH) | Cui, H. (GKSS-Forschungszentrum Geesthacht GmbH) | Recoschewitz, J. (GKSS-Forschungszentrum Geesthacht GmbH) | Dobernowsky, A. (GKSS-Forschungszentrum Geesthacht GmbH) | Szelagowski, P. (GKSS-Forschungszentrum Geesthacht GmbH) | Seeliger, D. (GKSS-Forschungszentrum Geesthacht GmbH)
ABSTRACT Operation of pipelines on the sea bed would not be possible without on-site installation, repair and exchange procedures. For such operations hyperbaric dry welding is the most favoured procedure. Dry hyperbaric welding operations could be classified in two distinct groups according to the working depth: manned operations (down to approximately 40Omsw) and diverless operations (at working depths beyond 500 msw). This study presents in its first part, a new orbital welding system for manned underwater operations based on a modular design which applies a Gas Tungsten Arc Welding (GT A W) module for the root and hot passes and a high deposition Gas Metal Arc Welding (GMAW) module for the filler and cap layers. Such modular concept results in an increased welding efficiency and thus reduced bottom times. The second part of this work. presents a conceptual description of the main element of a diverless repair station - the underwater habitat - consisting basically of robots and manipulators to prepare the pipe and to weld the spool piece. Also described are the main sub-systems of such a station, its working procedures and the R&D requirements to realize it. 1.0 INTRODUCTION Operation of pipelines on the sea bed would not be possible without on-site installation, repair and exchange procedures. Welding procedures carried out in hyperbaric dry environments are the most favoured procedures to perform such tasks since in this way the achieved mechanical properties comply with the applicable code requirements. Dry hyperbaric welding operations could be classified in two distinct groups according to the working depth: manned operations (down to approximately 40Omsw) and diverless operations (at working depths beyond 500 msw). In manned operations manual or semiautomatic procedures (SMAW, GTAW and GMAW) are normally applied where qualified and highly experienced welder-divers are employed [Delauze, 1989].
- Europe (0.46)
- North America > United States (0.28)