An effective method of protection of oil field pipes inner surface

Corrosion is a key factor, effecting service life of field pipelines. A review of methods of protection of circle welding seam internal surfaces and adjacent end pipe areas presented in the paper, as well as their imperfections, a technology proposed to protect them by arc building-up corrosion-resistant coating. With the elaborated technology the pipe metal does not get considerable overheating, retaining correspondent level of mechanical properties. The properly selected parameters of building-up mode provide a minimal stirring in the process of building-up and the decrease of concentration of main alloying elements (Cr and Ni) in the protective layer does not exceed 20%. To determine the minimal length of protective layer, manual arc welding and welding in protective gases atmosphere by consumable electrode were considered as possible welding methods. Simulation in the program complex SYS-WELD enabled to determine the areas subjected to critical heating, what was confirmed by the data, obtained during imitation of a circle seam in laboratory conditions at 159×8 mm short pipe. The proposed technology excludes the porosity of the built-up layer and other defects, decreasing the efficiency of pipe metal protection. Content of alloying elements was selected, for the built-up coating to be inclined to passivation and to have high resistivity against corrosion processes. Total corrosion rate at the tests in an acid solution, having hydrogen sulfide, was less than 0.1 mm/year thanks to austenite structure. The efficiency of the proposed technology was confirmed by positive results of pilot-field tests at a by-pass line under conditions of Sutorminskoje oil, gas and condensate deposit.

Pipe metal and welded connection defect repair by cladding

Cladding repair is the one of the most simple and least expensive repair technologies. It refers to both permanent and temporary repair methods. It reduces work costs and time of repair works while retaining the quality required by the statutory requirements. With the help of cladding repair, a significant number of defects of corrosion-mechanical origin can be eliminated. The problem of improving this technology is of utmost importance. The purpose of the present research is to develop the technology for effective and safe cladding repair of such defects as corrosion damages of pipe metal and such welded connection defects as incomplete groove filling, undercut, pores, strikes, slag inclusion. The following problems were solved to reach this goal: research of thermal cycles in the course of cladding, research of cladding modes, development of multipass repair technology, determination of allowable defect parameters, and detection of methods for optimal quality control of repaired areas. The specialists performed testing of full-scale pipe samples and circular joint of pipes, imitating the surface defects after cladding repair. The test results did not reveal the damage of metal and welded connection areas. Cladding repair allows recovering bearing capacity of pipeline to design level. This technology can be used in the works on shutdown pipelines and on pipelines under operation.

Study of factors enabling initiation and behavior of grooving corrosion

The work describes the experimental definition of the main factors that contribute to the emergence of grooving corrosion: availability of abrasive particles in flow which are transported in specific terms when they are capable of scratching the bottom generating line of a pipeline by creating stress concentrators; availability of considerable residual stresses in pipe metal; oxygen availability in reaction zone.