《船舶结构损伤事例》.ppt

Hull Structure Damage Examples Zhao Geng Xian（MARIC） Zhan Zhi Hu（CCS）,2010.12.8,Over the past few years, the author has handled some structure damages of ships and offshore structures for related companies and departments. Statistics shows that the damage rates of: Container Ships23% Bulk Carriers31% Oil Tankers23% RO/RO15.4% Offshore7.6%,We can draw conclusion from these accidents that the global strengths of these ship hulls are all reliable enough. Actually, these damages are mainly caused by the local structure damages and some of them are serious. The causes lie in many aspects such as design, production and application.,Hull Structure Damage Examples 1， Container Ships 2， Bulk Carriers 3， Oil Tankers 4， RO/RO,1， Container Ships,（a）4100 TEU Container Ship After 3 months service at sea, cracks were found among 6 of these sister ships. They were mainly located at hatch coamings, main decks and longitudinal bulkheads in the second cargo holds. These cracks firstly generated from the weld beads of the main decks, then grew and propagated to upper hatch coamings and lower longitudinal bulkheads. Cracks were also found at the platforms of these containers.,The cause for these damages lies in the incorrect treatment of ends of hatch coamings. In addition, the weld beads of the main decks were also improperly located (the folds of hatch coamings coincide with the weld beads between high-strength steel and low carbon steel). The transition of the plate thickness is also unreasonable.,（b）5668 TEU Container Ships Two longitudinals on the bulkhead were broken, and there was a 1.2 m long crack on the longitudinal bulkhead. It can be concluded that the span of these longitudinals in high stress area are too long to provide sufficient strength for avoiding longitudinal plate from buckling.,Two longitudinals on the bulkhead were broken,（c）500 TEU Container Ship After 10 years service at sea, Long-term slashing of sea water upon the bow side shell (between upper deck and forecastle deck) engendered a hole on it, which directly lead to sea water leaking into the tanker. As shown in Fig.2, warping of many transverse web frames on the side shell, break of shell girder and buckling not only of pillars but also of its lower brackets have occurred. They are mainly caused by ill consideration of impact pressure of sea water and green water, so the strength of plate panels of main deck and shell is undoubtedly insufficient.,Hole on the side shell (the complementary plate is temporarily fixed by the crew),break of shell girder (the complementary plate is temporarily fixed by the crew),Buckling of the pillar,Buckling of low bracket of the pillar,2， Bulk Carriers,（a）175,000 DWT Bulk Carrier Violent vibration occurred at the radar mast. It is mainly caused by underreinforced stiffen of stiffeners and insufficient structural reinforcement.,（b） Crack on Longitudinal Bulkhead of the VLOC After conversing VLCC into VLOC, a noise that sounded like explosion was heard when it was being conducted a strength test at sea (the height of water pressure is only 17m). There was a crack on the longitudinal bulkhead. It is mainly caused by Structure detail unsuitable,(c) 70,000 DWT Bulk Carrier After 5 years service, many cracks were found at connection not only of lower stool with corrugated bulkhead but also of hopper with inner bottom, which resulted in ballast water leaking into the cargo hold. Side longitudinals were broken after 5 years services.,Crack at connection of lower stool with corrugated bulkhead in A ship,Crack at connection of lower stool with corrugated bulkhead in B ship,Crack at connection of hopper with inner bottom,Side longitudinals were broken after 5 years services,They are caused by welding fatigue and the insufficiency of strength of longitudinal.,3， Oil Tankers,Sea water flooded into hold in course of its service at sea. It was caused by the improper handling of the end of the bottom longitudinal.,(a) Large Oil Tanker,Sea water flooded into hold in course of its service at sea.,Weld bead of stiffeners of the inner bottom was tore up at the corner,the crack was also found at the toe of the horizontal girder of bulkhead,3.2 110,000DWT Oil Tanker The deck was broken when the shipyard was conducting an air tightness test of the hold. It was affirmed that the test procedure was mistaken.,（c）49,000DWT Oil Tanker During its second voyage after delivery, alarms for oil-gas concentration in the ballast water tank arose. A 400mm long crack was found in the inner bottom. The crack occurred from the inner bottom where is around the lower stool of corrugated bulkhead, extending backwards in 45direction, and finally ended at the deep bracket of the initial lifting lug . Resulting in 30 tons of product oil leaking into the bottom ballast water tank.,The cause lies in that the lifting lug was improperly installed in course of hull erection of the bottom sections and new shear stress accumulated in the inner bottom, which afterwards couldnt release until external force acted upon the inner bottom.,4， RO/RO ship,4950 RO/RO ship Crack occurred at the transverse tripping bracket ob the vehicle main deck, as shown in Fig.10. It was caused by the insufficiency of shear stiffness of the transverse tripping bracket.,Summary and suggestions,Based on damage cases and analysis mentioned in this paper, some useful suggestions are presented as follow:,(1) Strengthen quality management during the process of construction. More attention should be paid to the construction procedure, especially welding and weld inspecti