A　large　number　of　cracks　are　found　in　the　1500m3　Liquefied　Light　hydrocarbons　vessel　during　the　inspection　after　two　years　of　running.　In　totally,　six　vessels　being　fully　heated　treated　is　made　of　15MnNbR.　Researchers　used　X-ray　stress　analyzer　measured　the　welding　residual　stress　of　vessels　that　have　been　cracked　and　uncracked.　The　results　show　that,　residual　stress　of　uncracked　spherical　vessels　are　in　good　condition,　while　those　value　of　cracked　is　high,　the　value　of　the　highest　is　1.05σs.　It　indicates　that　the　possible　reason　for　the　separation　is　the　residual　stress　in　the　high　state.　Through　welding　and　heat　treated　for　the　second　time,　the　welding　residual　stress　decreased　obviously.　It　indicates　the　impact　of　this　measure　is　good.　©　(2014)　Trans　Tech　Publications,　Switzerland.