划重点！带你学《化学品船安全指南》(八)-物理特性(中英双语)
阈限值是时间重量加权平均值TWA，表示工人每天工作8小时、每周工作40小时，日复一日地暴露在该环境下而健康不受影响的最高允许浓度，可以用短时间暴露的允许浓度STEL进行补充说明。
Chemical tankers are designed and equipped to transport a wide range of different cargoes and often carry a large number of products simultaneously. The operation of chemical carriers differs from that of oil tankers in that, on a single voyage, a large number of cargoes with different properties and inherent hazards may be carried. In port, several products may be handled simultaneously at one berth, typically involving such different operations as loading, discharging and tank cleaning.
海上运输散装化学品不仅仅是对船舶和设备有特殊目的的要求，对船员也有要求：化学品船的船员需要接受特殊培训，涵盖理论和实操两个方面，以使得他们能够知晓不同化学品的特性和在货物操作中潜在的危害。
The transportation of bulk chemicals by sea not only requires purpose built ships and equipment, but also seafarers who have received specialist training, both theoretical and practical, in order to understand the properties of the various chemicals and the potential hazards involved in cargo operations.
计划承运化学品时，船上的船员和船舶管理公司必须获取每一票货物的完整资料以确保符合国际上关于储存、操作和运输的要求；而且，货物的详细资料应向船上的船员提供如何安全操作该货物以及减少货物操作可能给环境带来影响的所有信息。
When planning the carriage of chemical cargoes it is essential that the ship's crew and the company managing the vessel are provided with a full specification of each cargo in order to ensure compliance with international stowage, handling and carriage requirements. Furthermore, the cargo details should provide the ship's crew with all of the information that they may require in order to handle the cargo safely and to minimise the impact that cargo operations may have on the environment.
1.2.1 密度和比重
Density and specific gravity
密度是指单位体积内某种物质的质量，通常用标准单位kg/m3来表示。
Density is defined as the mass of a substance per unit of volume, usually expressed in the standard (SI) unit kg/m3.
比重是指一物质单位体积的质量与相同体积淡水的质量之比。比重是一个比值，因此没有单位；比重随温度的变化而不同。常常会看到比重的后缀有20°C/4°C，是表示该物质20°C温度时的密度与4°C温度的水的密度之比。选择水的温度为4°C的理由是这个温度下水的密度达到最大的1,000kg/m3。
Specific gravity(SG)is the ratio of the mass of a product when measured against the mass of an equal volume of water. Because specific gravity is expressed as a ratio, it has no measurement units. However, the SG can vary according to the temperature of the product. It is quite common to see the SG quoted as 20°C/4°C, which refers to the density of the product at a temperature of 20°C referenced against the density of water at a temperature of 4°C. This temperature reference is selected because water has its maximum density of 1,000kg/m3 at 4°C.
作为化学品船，其设计参数标明了每个货舱能装载的货物最大比重(即常说的货舱设计比重)。同一艘船的不同货舱的设计强度可能不同，因此不同的货舱其能装载的货物最大比重和最大装载率也不同。
For chemical carriers, design parameters specify the maximum density of products that can be carried in each cargo tank. The design strength can differ between various tanks on board the same ship, resulting in different maximum densities and maximum filling ratios.
关于货舱强度的资料可以在船级社的说明书中找到，装载较大比重的货物时船长应熟悉这些限制可能带来的影响(即货物的比重大于货舱设计比重时的装载限制)。由于不满舱装载会产生液体晃荡， 其冲击力会破坏货舱结构或内部安装和设备。船上必须了解这些风险并尽可能避免不满舱装载。船级社提供了多种格式的货舱构造强度的相关资料，船长必须了解这些限制并严格遵守。
The information regarding tank strengthening can be found in the classification society's specifications for the ship, and the Master should be familiar with any restrictions that may be imposed when loading high density cargoes.
Especially important is the need to be aware of and avoid the risk of slack loading a tank. This is because slack loading can lead to sloshing forces that may cause damage to the tank structure or its internal fittings and equipment. Classification societies provide information about tank strength in various formats and the Master should ensure that the restrictions are understood and that there is full compliance.
Volume expansion coefficient
虽然货物的质量不会因为温度变化而不同，但通常它的体积会随着温度的升高而膨胀，因此货物的密度会随温度变化而不同。
Whereas the mass of a product does not vary with temperature its volume generally expands with increasing temperature. As a consequence, the density will vary with temperature.
对于石油产品，体积修正系数是使用美国材料与试验协会(ASTM)的标准进行计算的。
For petroleum products, volume correction factors are calculated using American Society for Testing and Materials(ASTM) tables.
对于化学品，运用以下公式将标准温度下(通常指20°C)的密度转换成实测温度时的密度：
For chemicals, density at standard temperature(usually 20°C)is converted to density at the actual temperature, using the following formula:
在MSDS或者产品数据库中通常没有注明密度修正系数，需要向码头长或商检索取。
Density correction factors are usually not stated in the MSDS or commodity databases, and will typically be obtained from the loading master or cargo surveyor.
例如：甲醇 For example: Methanol
装货时货舱应留有一定的空间，以备航行途中外部温度升高或相邻舱室高温货物的传导而出现货物体积膨胀。
Sufficient space must be allowed in the tank for expected expansion of cargo during the voyage due to a rise in outside temperatures or of cargo being similarly affected by heated cargoes in adjacent tanks.
计算单舱最大装货体积(Vmax)的适用公式如下：
A useful formula for calculating the maximum volume of a cargo to be loaded in a tank(Vmax)is:
Melting point
熔点是指某物质从固态变成液态的温度，处于熔点的物质其固态和液态保持平衡状态。某物质从液态变成固态的相反过程的温度称之为凝固点或结晶点。大多数纯净化学品(是指达到规定品质要求的产品)的熔点和凝固点基本相等。然而，一些产品例如植物油、木馏油、滑油添加剂和清洁石油产品，因其品质变化而无法给出一个确切的熔点，只能给出相应的范围。
The melting point of a product is the temperature at which it changes from the solid to the liquid state. At the melting point, the solid and liquid phases exist in equilibrium. The temperature of the reverse process when a product changes from a liquid to a solid is referred to as the freezing point or crystallisation point. For most pure chemicals(which are products with a defined quality specification)the melting and freezing points are approximately equal. However, some products such as vegetable oils, creosote oil, lube oil additives and clean petroleum products, whose quality varies, do not have a defined melting point but a melting range.
货物的熔点高于船舶航行区域的环境温度时需要对货物进行加温以保持其液体状态；船舶结构和设备对加温货物的最高温度带来了限制，这个限制将于文件的形式存放在船上；温度高于这个限制将损坏货舱涂层或相邻舱室如压载舱的涂层，同时，过热还会在舱室的钢结构上产生热应力并带来结构损坏的风险。
Cargoes with a melting point above the ambient temperature of the ship's trading area will need to be heated in order to remain liquid. The structure and equipment of a ship can impose a limitation on the carriage of heated cargoes, which should be documented on board. Exceeding this limitation could damage the cargo tank coating or coatings in adjacent spaces such as ballast tanks. Excessive heat will also create thermal stresses within the steelwork of the tank and risk structural damage.
运输高温货物时必须保持警惕，在无保温的管线和透气系统中货物将凝固。如果透气管线或透气管被堵，货舱中将出现真空或压力过大，造成货舱结构损坏。
Caution should be exercised when carrying high heat products. Cargo in non-insulated pipes and vents may freeze. Should vent lines or vents be blocked structural damage may occur due to a vacuum or overpressure developing within the tank.
Vapour pressure
液体的蒸气压力是指当液相和气相处于动态平衡时的蒸气压力。在恒温下的密闭系统中，当蒸气压力保持恒定时， 液体分子在挥发的同时气体分子也在冷凝。
The vapour pressure of a liquid is defined as the pressure exerted by its vapour when the liquid and vapour phase are in dynamic equilibrium. In a closed system at constant temperature, liquid molecules are evaporating and vapour molecules are condensing, while the pressure remains constant.
温度升高时蒸气压力也上升，因此在标明某一蒸气压力时需标上上对应的温度。
Vapour pressure increases with temperature, so when stating a vapour pressure it is also important to state the temperature.
蒸气压的单位为kPa(100kPa=1bar=14.5psi=0.99atm)，在常温时具有高蒸气压的产品称之为挥发物。
Vapour pressure is expressed in kPa(100kPa=1bar=14.5psi=0.99atm). A product with a high vapour pressure at ambient temperatures is referred to as volatile.
Boiling point
沸点是指某一液体的蒸气压力等于液体外部环境压力时的温度。液体的外部压力越低其沸腾的温度也越低。
Boiling point is defined as the temperature at which the vapour pressure of a liquid equals the external pressure that is surrounding the liquid. The lower the external pressure the lower the temperature at which the product will boil.
在封闭的货舱中，当蒸气压力等于外部压力加上P/V阀的设置压力时液体将沸腾。
In a closed cargo tank, a liquid will boil when the vapour pressure is equal to the external pressure plus the pressure setting of the pressure/vacuum(P/V)valve.
IBC Code要求温度在37.8°C时，蒸气压力大于101.3kPa(也就是说其沸点低于37.8°C)的货物只能装在具有机械冷却系统或者其结构强度能够承受该货物在45°C时的蒸气压力的货舱内。
The IBC Code requires that cargoes with a vapour pressure above 101.3 kPa at 37.8°C(in other words a boiling point below 37.8°C)can only be loaded in tanks that have a mechanical cooling system or that are able to withstand the vapour pressure of the cargo at 45°C.
Vapour density
蒸气密度是指在已知的蒸气体积中的蒸气质量与等体积的空气质量之比。将空气的密度比作1，就能很直截了当地判断某蒸气是比空气重还是轻。
Vapour density is the ratio of the mass of a given volume of vapour relative to the mass of the same given volume of air. Air has an arbitrary vapour density of 1, which makes it very straightforward to see if a particular vapour is heavier or lighter than air.
在压力和温度恒定的情况下，蒸气密度与该物质的分子质量成正比。
At constant pressure and temperature, vapour density is proportional to the molecular mass of the product.
大多数的化学品货物的分子质量大于空气，意味着这些货物的蒸气也比空气重。在货物操作和洗舱作业时须特别小心在甲板上的半封闭区域和封闭舱室中的底部可能积聚高浓度货物蒸气的安全隐患。
Most chemical cargoes have a molecular mass higher than air, which means that their vapours are heavier than air. Particular care must therefore be taken during cargo and tank cleaning operations because vapour concentrations are likely to accumulate in semi-enclosed areas at deck level and at the bottom of enclosed spaces.
Viscosity
粘度是度量液体流动阻力的指标，或者在通用术语中它是液体“浓度”的度量指标。
Viscosity is a measure of the resistance of a liquid to flow, or in more general terms it is the measure of the `thickness' of the liquid.
运动粘度是量度在特定温度下已知体积的液体在重力作用下的流动速率，它是测量每单位时间内的表面面积，通常用平方毫米/秒表示，由此通常将1平方毫米/秒称之为1厘沲(厘沲)。
Kinematic viscosity is a measure of the rate at which a known volume of liquid flows under the force of gravity at a specific temperature. It is measured in terms of surface area per unit of time, usually mm2/second, whereby 1 mm2/second is more commonly known as 1 centistoke(cSt).
动态粘度是度量在已知的温度下液体在外力的作用时其流动的阻力。它等于运动粘度乘以流体的密度，单位用毫帕-秒(mPa.s)表示。
Dynamic viscosity measures the resistance of a liquid to flow under an applied force at a given temperature. It is equal to the kinematic viscosity multiplied by the density of the fluid and is expressed in millipascal-seconds(mPa.s).
粘度决定了货物的泵送特性和卸货后的残留量。
The viscosity of a cargo determines its pumping characteristics and the amount of residue that may be left after unloading.
对于大多数产品，粘度随温度的升高而降低。然而，某些特定产品在加温时由于其化学结构的变化而使粘度随温度的升高而升高。
For most products, viscosity decreases with increasing temperature. However, certain products show increased viscosity when heated due to changes within their chemical structures.
Water solubility
水溶性既可以用百分比来表示也可以用溶解度来表示(比如“不溶”、“微溶”或“全溶”)。
Solubility in water can either be expressed as a percentage or graded (i.e. ‘nil',‘slightly' or‘complete').
水溶性取决于该产品的分子极性和分子内碳原子的数量和长度。碳氢化合物(烃类)如石蜡(链烷烃)和烯烃均为无极性的，它们不溶于水(即溶解度<0.01％)。
Water solubility depends on the molecular polarity of the product and the number and length of carbon atoms within the molecule. Hydrocarbons such as paraffins and olefins are non-polar and insoluble in water (i.e. solubility<0.01%).
含氧的碳氢化合物，如醇、酮、酸、酯和醚，由于碳链的长度较小(通常的最大值为3-4)往往更易溶于水。水溶性随着碳氢链中的碳原子数目的增加而急剧下降。
Hydrocarbons containing oxygen, such as alcohols, ketones, acids, esters and ethers, tend to be more soluble in water as the length of the carbon chain is small(typically 3-4 maximum). As the number of carbon atoms in the hydrocarbon chain increases water solubility rapidly decreases.
水溶性也与温度有关系，大多数产品的溶解度随着温度的升高而增加。
Solubility is also temperature dependant. For most products solubility increases at higher temperatures.
微溶或不溶于水的货物会在水层上方或下方形成一个分离层，这取决于货物的密度是比淡水的密度(1.00吨/立方米)大还是小。许多不溶于水的货物的密度比水的密度小，因此会浮在水面上。最常见的比水重的碳氢化合物是氯化溶剂，这些货物与水混合时往往会沉在货舱底部。
A cargo with little or no solubility in water will form a separate layer above or below the water layer, depending on the density of the product relative to fresh water, which has a density of 1.00 tonnes/m3. Many water insoluble products have a relative density less than 1.00 and will float on top of water. The most common group of hydrocarbon cargoes that are heavier than water are chlorinated solvents which will sink to the bottom of the tank when mixed with water.
来源：中国船检国际传媒
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