E N G I N E E R I N G C O P P E R

S O L U T I O N S

KME

Ger

man

y G

mbH

& C

o. K

GSP

ECIA

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IVIS

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[EN

/CN

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TUBE BUNDLES

90-10 Copper-Nickel vs. Type 316 Stainless SteelA functional comparison of two tube bundle alloys

铜镍90/10合金与316不锈钢

两种用于多芯管材料的功能对比

Stainless Steels in Tube BundlesChloride-rich seawater is a particularly harsh environment that can attack stainless steel by localised corrosion. Type 316 grades are used widely in marine applications, but their corrosion resistance in contact with seawater is limited and they cannot be considered 'corrosion proof' under all situations.

Crevice and the closely related pitting corrosion mechanisms are the predominant forms of attack that are normally responsible for the failure of the 316 types in seawater service, limiting the scope for their use. In the case of tube bundles, if the outer sheath becomes damaged, stainless steel tubes have proved unsuccessful, as shown in figures 1-4.

Even, a small cut in the outer sheathing is sufficient to cause corrosion damage of the whole tube bundle. Under practical conditions, damage to the outer sheathing due to carelessness during installation can never be completely excluded.

Improper or wrong installation of heat-shrinkable dividing caps can lead to rapid tubing failures due to crevice corrosion in the gaps formed, as shown in figure 3. Installation of polymer-sheathed tubing requires the use of special tools and specially trained pipe fitters that are capable of working with this product without causing any damage. In particular, this includes ensuring weatherproof end sealings of the tubing at the pipe fittings and deck penetrations. Only a complete, moisture-proof, tube fitting connection secures protection against corrosion. Any form of damage or incomplete shrinking of tube bundles containing stainless steel tubing must be avoided to ensure reliable service performance.

All the above findings lead to the strong possibility that seawater and moisture could get into the tube bundle. Due to the capillary action, the water/moisture can get up to 60 metres into the tube bundles even if there is just small damage to the outer sheathing. This was tested and confirmed at the KME laboratory. The combination of seawater inside the tube bundles and the different outside temperatures can lead to the corrosion of the stainless steel tubing and therefore leakage.

Figure 1-2: Cuts and cut-offs due to abrasion from the cableway

图1-2: 在多芯管通道上遭受的割缝和裂口

Figure 3: Tube failures as a result of crevice corrosion图3: 由于裂隙腐蚀所导致的管路失效

Figure 4: Corroded 316 tubing, leading to fluid leakage图4: 受到腐蚀的316管路,导致了流体泄漏

用于多芯管的不锈钢

富含氯化物的海水是非常严酷的外部环境,它会导致不锈

钢材料发生局部腐蚀。316不锈钢被广泛地应用到了海洋

环境中,然而由于其在接触海水情况下的耐腐蚀能力非常

有限,因而不能认为它在任何条件下都是“耐腐蚀”的。

裂隙和与其密切相关的点蚀是316不锈钢在海水环境下

发生腐蚀并失效的主要原因,正因为如此,其应用范围受到

了限制。如果多芯管的保护层受到损坏,其内部的不锈钢

管将不会得到成功的保护,这种实例如图1-4所示。

即使是保护层上出现了一个小的裂口,也足以导致整个多

芯管的损坏。而实际上,在施工时由于不小心而导致保护

层损坏的情况是无法完全排除的。

安装不当或者错误安装热缩型保护盖,也会由于在其间隙

中发生裂隙腐蚀而导致管路失效,正如图3所示。安装聚

合物保护层需要使用特殊工具,由接受过专门训练、可以

正确安装管路而不致其受损的合格安装工来完成。尤其

是,还要确保在管配件和穿舱部位防风雨端的完好密封。

只有完整且能抵御风雨潮湿的管路连接才能避免发生腐

蚀。任何对(由不锈钢管制成的)多芯管的损伤或热缩材料

保护的不完整,都要严格避免,从而确保其使用性能。

所有的上述错误都很有可能导致海水和湿气进入多芯

管。即使是在外部保护层上发生了小的损伤, 水和湿气也

会由于毛细作用而进入多芯管达60米左右。这一点已经在

KME的实验室里通过实验得到了验证。海水在多芯管内

外的不同温度变化的综合作用将会使不锈钢管发生腐蚀

进而出现泄漏。

It is well known that pitting and crevice corrosion of austenitic stainless steels are strongly influenced by the presence of chlorides and temperature. Figure 5 shows a graph giving the temperature at which corrosion is likely to occur. Temperature on deck can often reach more than 50°C so that even alloys containing 4% Mo or more could also fail due to pitting or crevice corrosion.

The Pitting Resistance Equivalent Number (PREN) has been found to give a good indication of the pitting resistance of stainless steels. This indicator has been widely advocated by stainless steel manufacturers and has gradually been accepted by users over the past decades. For austenitic grades the PREN can be calculated as:

PRE = %Cr + 3.3 x %Mo + 16 x %N

The higher the PREN value of an alloy, the higher its resistance to localized corrosion, i.e., the higher it’s critical pitting temperature (CPT) and critical crevice corrosion temperature (CCT). Low alloy stainless steels, such as 316L (PREN is well below 30) will suffer pitting and crevice corrosion in sea water.

Even higher alloy stainless steels, such as 904L and 22%Cr duplex, suffer crevice corrosion in ambient temperature seawater. Only alloys with a PREN greater than about 40 have been shown to resist crevice corrosion in ambient seawater.

众所周知,奥氏体不锈钢的点蚀和裂隙腐蚀受氯化物和

温度的影响非常大。图5列出了温度与可能发生腐蚀的

的关系。由于甲板上的温度往往会超过50度,所以即使

是含有4%甚至更高的钼的合金,也会由于点蚀和裂隙腐

蚀而失效。

点蚀当量数(PREN)是衡量不锈钢耐腐蚀能力的一个很

好的指标。这一指标已经被大量的不锈钢生产厂家所提

倡且在过去的几十年里被用户所接受。这个公式是:

PREN = %Cr + 3.3 x %Mo + 16 x %N

合金的点蚀当量数PREN越高,其抵御局部腐蚀的能力越

强。低合金不锈钢,比如316L(PREN低于30)将会在海水

中受到点蚀和裂隙腐蚀。

即使是高合金不锈钢,如904L和含22%铬的双相不锈钢,

也会在环境温度下遭受裂隙腐蚀。只有当合金的点蚀当

量数PREN大于约40的情况下,它才具有在海水环境温度

下抵御裂隙腐蚀的能力。

Tem

pera

ture

(°C

) 温

度

Critical Pitting Temperature (CPT) 临界点蚀温度

Critical Crevice Temperature (CCT) 临界裂隙腐蚀温度

Figure 5: Critical pitting and crevice temperatures for different alloys, rated by ASTM G48 tests

图5: 不同合金的点蚀和裂隙腐蚀的临界温度(由ASTM经G48实验得出)

Figure 6: 90/10 CuNi tubing

图6: 铜镍合金90/10管路

Figure 7: Tube bundles

图7: 多芯管

Material

材料

Uniform corrosion

均匀腐蚀

Pitting/Crevice corrosion

点蚀/裂隙腐蚀

SCC

应力腐蚀裂纹

Biofouling resistance

抵抗海生物生长

Effect of chlorination

氯化处理的影响

Effect of temperature

温度的影响

Standard Stainless Steel

标准不锈钢++ – – – + +

90-10 CuNi

铜镍合金90/10++ ++ ++ ++ ++ ++

– Not resistant, not suitable 不耐腐蚀,不宜采用

+ Potential problems, life time, design restrictions, etc. 有潜在问题,使用寿命短,设计时受限

++ Satisfactory 效果好

用于多芯管的铜镍合金90/10

而铜镍合金则是专门用来解决海水环境下出现的这些问

题的。当外部保护层受损时,比起不锈钢来,铜镍合金抵

御腐蚀的能力会使其坚持更长的时间而不被腐蚀(如图

6-7所示)。

在海水环境下,铜镍合金展现出了非常出色的抵御点蚀

和裂隙腐蚀的能力。

之所以铜镍合金在海水环境下有着非常出色的性能,

是由于其构成颇为复杂的表面保护膜与其自身抵御

海生物生长能力的综合作用的结果。比如铜镍合 金

90/10(C70600),它已经在海洋工程、海水淡化和沿海工

业等海水处理领域里被成功地应用了很多年,有着非常

良好的记录。

90-10 CuNi in Tube BundlesHowever, copper-nickel alloys have been designed to cope with these problems in the seawater environment. When the outer sheathing becomes damaged, it will take much longer time for the CuNi tubing to corrode in comparison to stainless steel as shown in figures 6-7. The copper-nickels display excellent resistance to chloride pitting and crevice corrosion in seawater.

The superior seawater performance of copper-nickels is the result of the nature of the protective complex surface film combined with high biofouling resistance. 90-10 CuNi (C70600), for example, has a long record of successful installations for seawater handling within offshore, desalination, and coastal process industries.

Further KME information: 有关KME的更多信息请阅读以下样本

OSNA®-10关于海洋工程镍铜包敷材料的样本

OSNA®-10/OSNA®-30关于船舶管路系统材料的样本

Copper-Nickel Seawater Piping System关于海洋工程管路系统材料的样本

OSNALINE®

多芯管