Abstract
This paper studies the corrosion mechanism of the weld seam of the submarine pipeline’s spool. The types and causes of inner tube weld corrosion are simulated by EDX and XRD analysis of the on-site pipe corrosion products, combined with OLGA Software simulation pipeline flow pattern. The tensile testing, impact testing and hardness testing were carried out on the base metal and the weld by tensile tester, pendulum impact tester and Brinell hardness tester to analyze the mechanical properties of the base metal and the weld; the microstructural difference between the weld and the base metal were analyzed by optical microscopy; The results show that the liquid phase flow rate along the line is between 3.5m/s and 7.5m/s, which aggravates the mixing between the gas and liquid phases to form a bubble flow. When the entire weld area is immersed in the same simulated medium solution, the galvanic corrosion occurs in three parts of the weld zone. The weld seam and heat affected zone will be accelerated to corrode as the anode region of the galvanic couple. The weld seam has the lowest corrosion potential and is always used as an anode to accelerate corrosion.
Highlights
The submarine pipeline is the lifeblood of offshore oil and gas gathering and transportation [1]
Pipeline steel will undergo a series of unbalanced thermal cycling processes during welding, resulting in uneven distribution of microstructure of pipeline steel welds, inclusions, hardened microstructure, poor mechanical properties and the result of galvanic corrosion in the weld zone results in a decrease in the corrosion resistance of the weld
During the welding process, the pipeline steel base metal and the weld zone need to undergo a series of complicated non-equilibrium thermal cycles, resulting in uneven microstructure of the weld and possibly welding defects
Summary
The submarine pipeline is the lifeblood of offshore oil and gas gathering and transportation [1]. Pipeline steel will undergo a series of unbalanced thermal cycling processes during welding, resulting in uneven distribution of microstructure of pipeline steel welds, inclusions, hardened microstructure, poor mechanical properties and the result of galvanic corrosion in the weld zone results in a decrease in the corrosion resistance of the weld. During the welding process, the pipeline steel base metal and the weld zone need to undergo a series of complicated non-equilibrium thermal cycles, resulting in uneven microstructure of the weld and possibly welding defects. As a result of the thermal cycle of the weld, the microstructure of the welded joint changes significantly, and the composition and structure of the region become uneven, and the corrosion behavior is greatly affected. Corrosion of welded joints mainly includes local corrosion [7,8], stress corrosion [9,10] and galvanic corrosion [11,12]
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