The Research Of Weldability And Welding Procedure Of Offshore Platform’s High Strength Low Alloy Steel (EQ56,EQ70)

As offshore platform from shallow sea to deep sea, the steel grade and thickness whichoffshore platform used is higher and higher. In this paper, the cold crack sensitivity of thehigh strength steel EQ56and EQ70are researched by Y-Slit Type Cracking Test, forfounding the competent consumable. For analysing microstructure and property of weldedjoints within different welding procedure by Flux-Cord Arc Welding (FCAW), we canchoice a suitable welding procedure specification for producting.EQ56has a good ability to resist cold crack by using DUAL SHIELD II101H4M.Comparing with DUAL SHIELD II101H4M, EQ56needs to improve preheatingtemperature to resist cold crack by using LMN MoNi. As more thickness and restrictiveness,EQ70shall improve preheating temperature to reduce cold crack sensitivity. Comparingwith OUTERSHIELD91K2-HSR, EQ70only needs lower preheating temperature to have agood ability to resist cold crack by using FLUXOFIL M42.Different preheat temperature, heat input and post-weld heat treatment will affectobviously the microstructure and mechanical properties of welding joints.Themicrostructure of weld center gained are pro-eutectoid ferrite and acicular ferrite.Thenumbers of pro-eutectoid ferrite and acicular ferrite change in different preheat temperature,heat input and post-weld heat treatment. Only when the microstructure of weld center isacicular ferrite, the high strength steel will gain good property of tesile strength and lowtemperature inpact.Summing up the results, the suitable preheat temperature, heat input andpost-weld heat treatment will get a qualified property about EQ56and EQ70.Comparing with the SMAW, the tensile strength and low temperature inpact propertyof EQ56and EQ70have being decreased by FCAW. But, the property of welding joints byFCAW still meets the requirements of ABS. In considertion of the effective of producting,the FCAW is more suitable than SMAW.