ClassNK approves friction stir welding

27 Mar 2012
The IHI-SPB tank is the type of structure suited to FSW; the design prevents sloshing due to weather conditions such as strong wind, enables transport with the tank partially filled, and should resist collision damage

The IHI-SPB tank is the type of structure suited to FSW; the design prevents sloshing due to weather conditions such as strong wind, enables transport with the tank partially filled, and should resist collision damage

ClassNK says that it has issued approval for a friction stir welding (FSW) method using a floating bobbin tool to IHI Corporation, certifying that this new method complies with ClassNK’s 'Guidelines on Friction Stir Welding'.

IHI is considering applying this welding method to the aluminum sections of LNG carriers and/or FLNGs cargo tanks such as the IHI-SPB tank,, which had been independently developed by IHI group at its Aichi Works.

The Japanese class society says that FSW is currently gaining popularity in some other industries thanks to its superiority to arc welding in a number of aspects, notably that it does not produce arc and fume at the time of welding and provides relative control over welding deformation. Its application is now limited to low melting point materials such as aluminum alloy or magnesium alloy because of the friction heat generated in the welding process. However, it is expected to become widely used in shipbuilding in relation to the construction of aluminum alloy structures.

Furthermore, according to ClassNK, this welding method is equipped with a solution to one of the common defects in FSW. Generally, a rod-like tool with a projection called a ‘pin’ is used in FSW, but it can result in a lack-of-penetration defect called a ‘kissing bond’, which occasionally occurs on the underside of the contacting surfaces depending on welding conditions. The new welding method, however, provides a solution to this problem with a special tool known as a floating bobbin. This tool is expected to effectively avoid the occurrence of kissing bonds by enabling double-sided welding.

ClassNK adds that as the demand for new technologies such as the above increase in the near future, it expects to be proactive in supporting their development and practical use as a third-party certifying body dedicated to ensuring the safety of life and property at sea.

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