SRT #31 - 船身呈裂缝船级社压力大 2012.01.02

2012-01-03 22:01  浏览次数 120

船身呈裂缝船级社压力大   

2012.01.02

劳氏日报0102

淡水河谷公司40万吨新船 “Vale Beijing” 经船壳扫苗后已证实船身发生裂缝,海水进入货舱,船上三部水泵正在日夜运作把舱内海水抽掉, 以便进行临时修补,然后开往葡萄牙或土耳其修理. 但开船前必需平好前后吃水把第七货舱之货移往第三和第五,专家认为出事原因是装货次序错误或船身结构出问题.

该轮由韩国 STX造船厂承造, 对此事件厂方声明该轮全部依照 DNV船级社所批准之蓝图及要求建造并否认工程进行中发生问题.

一般来说装载重货之前大副需做一份 “Shearing force and Bending moment” 计算,把货分开和分批来装 (loading sequence), 不能一次装满一个舱后再装笫二个舱, DNV为节省装货时间起息研发一种叫 “single pass-easy loading” 方式允许40万吨级之 VLOC每个货舱都可一次装满, 这对船壳来说确实增加极大的拉力. DNV在此之前早己把这个拉力计算好和包括在船壳钢板厚度要求之中, 但是裂缝还是发生了. ( 1).

 

Vale Beijing cracks confirmed

A FULL hull scan conducted by robot has confirmed cracks to the hull of very large ore carrier Vale Beijing, with the vessel’s three ballast pumps now working around the clock, according to a report from the Lloyd’s agent in the Brazilian port Sao Luiz.

Around 5,000 tonnes of heavy fuel oil will be removed to a barge over the next few days to reduce any potential risk of pollution, while part of the cargo from No 7 hold will be restowed into No 3 and No 5 holds.

According to hull and machinery underwriters, after some provisional repairs are carried out the 400,000 dwt ship will proceed, probably to Lisbon or Istanbul, for full repairs. Vale Beijing is operated by STX Pan Ocean.

The huge vessel, one of only five in operation, was on its maiden voyage earlier this month laden with almost 380,000 tonnes of iron ore when it began taking on water.

A crack in Vale Beijing’s ballast tanks was either the result of poor loading technique or a structural problem, an official with the Sao Luis harbour pilots’ service told Reuters at the time.

The ship was built at STX Offshore and Shipbuilding in Jinhae, South Korea, and inspected by Norwegian classification society Det Norske Veritas.

Bulk Carrier VLOC 'Vale Beijing' – Dry-dock Next Destination

A few days ago VLOC Vale Beijing was towed off the berth to avoid risk of foundering alongside the Vale iron ore loading terminal at Ponta Madeira, having earlier reported ingress of water to a partly loaded cargo hold. According to Lloyd’s List  a full hull scan by robot device confirmed cracks to the hull with the ship’s three ballast pumps working around the clock to contain the flow. What is the extent of the damage to Vale Beijing?

Vale Beijing Structural Damage

In a few words, the hull plating was found to have cracked in the vicinity of a water ballast tank, and from there water was making its way into a cargo hold. Vale Beijing is classed by DNV whose preliminary inspection reportedly described (in addition to the crack in outer hull plating) fairly substantial internal damage to web frames and longitudinals in the vicinity of the water ballast tank. Informed opinion considers such damage a likely consequence of excess localised stresses in the hull structure sustained while loading the heavy ore. An available dry-dock capable of handling the 362 m (1,188 ft) long VLOC is being sought.

              VLOC Vale Beijing Loading Iron Ore: Photo courtesy of STX

贸易风 2011.12.15

对淡水河谷新船发现裂缝一案调查人员将集中于DNV船级社在该船证书所签发之 “single pass-easy loading.

专家称将集中对装货之每小时 16,000吨速度进行详细调查.( 2 & 3).

   

Cracks probe to focus on fast loading

A controversial class notation in the operation of a brand-new Vale VLOC will be top of the agenda for investigators.

A controversial class notation from Norway’s Det Norske Veritas (DNV), which allowed the super-fast loading of the newly built Vale Beijing, is set to figure significantly in the investigation into why potentially catastrophic cracks appeared on the ship’s hull at Ponta da Madeira.

The massive 400,000-dwt very large ore carrier (VLOC), part of a series of 35, was built to DNV’s Easy Loading 2 (EL) voluntary notation, which allows each hold to be fully loaded in one go in what is termed “single-pass loading”.

It is understood that the Vale Beijing was being loaded, in what was its first loading, using this method when the cracks appeared.

Usually the holds of ore carriers are partially loaded in stages until they are full to reduce stresses. However, the commercial benefits of single-pass loading are massive, reducing loading time by more than half from 26 hours to less than 12 hours for a ship of this size.

But experts say the stresses on the hull during loading can also be enormous with loading rates at Ponta da Madeira reaching 16,000 tonnes an hour and localised shear forces acting on sections of the hull increasing as each hold is loaded in one go.

Photos of the vessel being towed after the cracks appeared show iron-ore waste around all cargo holds with the exception of the number five hold, suggesting that it was not loaded when the cracks appeared.

The depth of the vessel in the water also suggests it was not fully loaded and Vale officials have been quoted as saying that around 260,000 tonnes of cargo were on board when the cracks appeared.

Experts suggest that in that condition the shear forces on the hull would be greatest on the empty number five hold. However, the cracks have appeared on both sides of the ballast tanks surrounding the number seven hold.

One possible explanation being put forward is that the number seven hold is a region where the cargo hold connects to the engine room and longitudinal framing may change to transverse framing in the engine room and could be a region of possible weakness.

Yet the vessel’s hull will have been designed and built for all the expected forces brought about by the loading process. It is understood that the ship also had DNV’s CSA 2 notation, which allows the vessel to calculate fatigue and ultimate strength in the cargo area.

None of the other vessels delivered so far had any problems during loading.

However, as a specialised ore carrier, the Vale Beijing will not have been built to the common structural rules (CSRs) introduced by classification societies to improve the structural strength of standard bulkers and tankers. A problem in the building process could also be a factor. The vessel was built at STX Offshore & Shipbuilding and had dual classification by DNV and the Korean Register.

DNV says it is working along with the Korean Register to determine the cause of the accident but it could not make any official comment at this stage.

淡水河谷公司对这艘之要求是否急了一点?

Is Vale pushing the boat too far?

Vale’s massive commitment to 35 of the largest ore carriers ever built was made with the intention of maximising the efficiency and profit of its logistics business.

But the Vale Beijing accident now begs the question as to whether it has pushed things too far in pursuit of economies of scale.

The giant 400,000-dwt bulker was designed to load iron-ore cargo using what is termed single-pass loading (see story, page 42). This means each cargo hold is fully loaded in one pass rather than gradually loaded in stages, dramatically reducing the time the vessel spends in berth.

It was certified to use this loading method by a voluntary notation, “Easy Loading 2”, from classification society Det Norske Veritas (DNV), which approves that the vessel is strong enough to cope with the increased stresses.

But, for whatever reason, the ship’s hull fractured during the loading process. It could have been a construction fault, or it could have been an operational error in deballasting but owner STX, charterer Vale and class societies DNV and the Korean Register need to reassess whether these giant hulls can sustain the sort of pressures they are being put under during loading.

If the answer is negative then it will have huge implications for the economic rationale behind Vale’s project.

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