| The marine liquefied gas storage tank is one of the main loading equipment of the LPG carrier and is the core of the whole LPG ship.The manufacturing and welding of the liquid tank is the key to the construction of the whole LPG ship.Especially in the field of independent C-type full-pressure LPG manufacturing,the application of P690QL1 high-strength steel material in bi-lobe tanks is the first in the world.For the P690QL1 material welding of the bi-lobe tank,there are high performance requirements for weld joints,the Y joint has a tendency to weld cold cracks,and the welding quality is difficult to guarantee.This paper studies the welding process of P690QL1 high strength steel SMAW,FCAW and SAW for bi-lobe tank.In this paper,the P690QL1 welding preheat temperature,inter-pass temperature and post-heat temperature parameters are studied based on the theoretical analysis of the weldability of high-strength steel,which lays a theoretical foundation for the subsequent process research.On this basis,the welding process performance comparison test was carried out to determine the SMAW FCAW and SAW welding consumables.Then,the oblique Y-shaped groove restraint crack test,method of rigid restraint cracking test for welding butt joint and the highest hardness test in the HAZ heat affected zone are tested to determine the actual parameters of welding preheat,inter-pass temperature and post-heat temperature.Secondly,through the stress analysis of the 3D model of the bi-lobe tank Y-joint,the specificity of the Y-joint in the bi-lobe tank structure is illustrated.In view of the problem of high structural stress and high hardness of the joint heat affected zone,Mock-up welding test was carried out.In the case of rigid fixed and non-rigid fixed,different groove and welding sequence were used,and the use of weld toe was different.The tempering bead process of the lap joint determines the tempering bead process suitable for the welding sequence of the Y joint welding and the certain amount of overlap.Finally,the test parameters were obtained according to the manufacturing process of the liquid tank and the previous test.The welding procedure qualification test was carried out in the horizontal and vertical positions by SMAW,FCAW automatic and semi-automatic,SAW.Through NDT of joints,mechanical properties tests,and microscopic analysis of welds and HAZ,verifying the relationship between reasonable welding heat input,preheating and inter-pass temperature,post heat treatment and other parameters on welded joints and performance results.The final study results show that:(1)The carbon equivalent CEQ of test plate thickness of 45 mm is 0.52,and Pcm is 0.22,it has a certain cold cracking tendency,general weldability.Before welding,it needs to preheat 150℃,the inter-pass temperature is below 200℃,and the post-heat temperature is 250℃,time is 2 hours.(2)The Y joint side plate was prepared the K-shaped groove at 1/3 of the plate thickness of 45 mm,first adopts low-strength matching welding base on the 1/3 side,and is matched with the strong matching electrode,and then removes the root welding on the reverse surface carbon planer.Seam welding.The two sides are alternately welded five times,the side plate deformation of the Y joint is the smallest,and the stress on both sides of the joint is balanced.The tempered weld bead method with 60-70% overlap is used on the weld toe of both sides of the Y joint,which is 10% lower than the hardness of the tempering welding process with 30-40% of the load.(3)The test plate adopts SMAW,FCAW and SAW processes in the horizontal and vertical positions,the heat input is 15~20kJ/cm.Under the condition of suitable conclusion 1,good welded joints can be obtained.However,with the increase of heat input,the large heat input performance of vertical welding position is slightly weaker than that of horizontal welding small heat input performance.The weld grain becomes bigger and the lath martensite is large in the coarse grain area. |
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