A technology for treating inner surface of trunk pipelines in weld areas

Abstract

A technology for dressing and coating in weld areas on inner pipe surface and a device for its realization have been developed. The referred technology and device can be used to restore coatings damaged in the welding process, reduce hydraulic resistance, and extend service life of trunk pipelines.Currently, special attention is being paid in the oil and gas industry to extending service life of trunk pipelines. This life depends essentially on the quality of corrosion protection (prevention) of outer and inner surfaces of trunk pipelines [1].Various methods have been developed and are being used widely to protect the outer surface of pipes, especially in weld areas. For instance, after dressing of the weld, Trial-L type of thermosetting collar supplied by the St. Petersburg firm Khimbalt is put on it. The remaining part of the outer pipe surface is reliably insulated by what is called the VUS insulation supplied by the Moscow firm Evrotekhstroi. Such a technology helps extend the pipeline service life to as many as 20-25 years, but the cost in this case rises by 20-25%.Protection of the inner surface of trunk pipeline is, however, a more complicated matter [2]. Nowadays, some pipe rolling mills, particularly abroad, coat the inner surface of pipes either with Permacor type of special paint manufactured by the German firm Sika Korrosionschutz GmbH or with sand cement. Such coats not only extend the service life of the pipeline significantly but also reduce loss of power for pumping gas trough the pipe on account of diminution of its hydraulic resistance.However, wide application of inside coats is hindered due to difficulties associated with operations performed after welding.First, this involves "swabbing" of the pipe by running through it a specially made piston (a cleaning device fitted with cup-shaped sleeves and steel brushes) with the help of a pipe-layer and a long rod, purging of the pipe with air, and collection of the dirt [3]. Such a procedure for pipes with an inner coating is inadmissible because it damages the coating, but no other method is available yet. Pipe "swabbing" by three pistons is an indispensable operation stipulated by the Set of Rules for laying trunk pipelines [4].Second, when the butt joints of two trunk pipes having a factory-laid inner coat are welded, the coat in the weld area is destroyed completely. And precisely here begin irreversible corrosion processes.Solution of this problem is pressing when use is made of costly high-pressure pipes having a diameter of 1420 mm and a wall thickness of as much as 36 mm, which the Chelyabinsk Pipe Rolling Mill and Vyksa Metallurgical Works have begun to manufacture.The importance of solution of this problem is associated also with the immediate prospect of hydrogen energy development because on the efficiency of gaseous hydrogen pumping from the point of its production to the consumer depends the economic efficiency of introduction of hydrogen energy.