Hydrogen: Double-layer pipes for pipelines

Green hydrogen is indispensable for a climate-neutral energy supply. However, the transport and intermediate storage of gaseous hydrogen over long distances requires a durable pipeline network. Existing pipeline systems only fulfil this requirement to a limited extent, especially if the pipelines for gas storage are subjected to dynamic pressures. The so-called hydrogen expansion leads to fatigue cracks, particularly in the area of welded joints and generally in high-strength materials. This could be remedied by multilayer tubes produced using the hydroforming process (hydroforming), as demonstrated by the Fraunhofer Institute for Machine Tools and Forming Technology IWU as part of research work. The main advantage of the process is that no enclosing moulds are required, meaning that production is also possible for very long pipe segments and in the immediate vicinity of pipeline construction sites.

Today's transmission pipelines, i.e. pure transport pipelines, are made of high-strength steels and can be used for pressures of up to 30 bar without any problems. Only long-term (quasi-static) pressure changes occur. However, if the pipeline network is used dynamically to store significant quantities of hydrogen, the operating pressure range is between 30 and 100 bar. Such cyclic loading, also known as pipeline breathing, promotes the propagation of fatigue cracks due to hydrogen displacement, particularly at the welding seams, but also on high-strength pipe base materials. In the chemical industry or, for example, in the extraction of crude oil with a high sulphur content, multi-layer pipes are already being used, which are usually formed from roll-bonded sheet metal and seam-welded. This type of pipe is therefore unsuitable for hydrogen transport due to the large weld seams.

The research approach of the Fraunhofer Institute for Machine Tools and Forming Technology IWU was therefore to produce multilayer pipes specifically for the transport and storage of gaseous hydrogen while keeping an eye on resource efficiency. By using high-quality, thin-walled stainless steel pipes that are insensitive to hydrogen damage without any support function in the inner layer and easy-to-manufacture, high-strength, longitudinally welded pipes as the outer support layer, very safe piping systems can be produced cost-effectively and with reduced material usage.

Source: Ingenieur.de from 02/11/2022