Siemens MRI
Joint Redesign for Cryogenic Pressure Vessels

For many years, LTi Metaltech has been a trusted partner to Siemens, manufacturing the cryogenic pressure vessels that encapsulate the liquid helium essential to the operation of its MRI scanners. This case study focuses on the development of a new welded joint design, engineered to achieve full compliance with the AD2000 Merkblatt pressure vessel code, while also introducing Design for Manufacture (DFM) innovations to improve repeatability, quality, and efficiency.

The project formed part of a wider initiative by LTi Metaltech to deliver innovative manufacturing solutions that help customers reduce production costs, shorten lead times, and ensure consistency in quality at scale. For Siemens, the challenge was even broader: to cut overall manufacturing costs and lead times in MRI scanner production, strengthening its position as the global leader in medical imaging technology.

Siemens MRI- Joint Re design- Image 1
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The Challenge: Redesigning a Cryogenic Welded Joint

To meet Siemens’ requirements, LTi Metaltech needed to develop an alternative method of manufacturing the welded joint - one that was faster, repeatable, and more cost-effective, while still delivering the highest levels of performance and compliance.

The redesigned joint had to withstand extreme cryogenic conditions of -269.1°C (4 Kelvin), the critical point at which gaseous helium becomes liquid and is used to cool MRI scanners. At the same time, the joint needed to conform to Siemens’ tight geometric tolerances and achieve full compliance with AD2000 Merkblatt, the European code governing the design and manufacture of high-integrity pressure vessels.

In pressure vessel fabrication, weld repeatability is paramount. Consistency and quality cannot be sacrificed for speed, as identical welds must be produced with the same angle, speed, distance, and accuracy every time. Traditionally, this depended on highly skilled welders with years of experience, supported by regular inspections to maintain compliance with strict standards. For Siemens’ original joint design, however, achieving repeatability at scale would have been even more challenging.

Yet, when achieved, welding repeatability brings powerful advantages: not only does it ensure compliance and consistent quality, but it also drives significant cost savings by reducing the likelihood of rework and delays.

For MRI technology, the stakes are even higher. To generate body images, MRI scanners must produce a powerful magnetic field using a superconducting magnet and coils of wire carrying electrical current. The liquid helium within LTi’s cryogenic pressure vessels is critical to this process, cooling the magnet coils to super-low temperatures that reduce electrical resistance to almost zero. This enables superconductivity - the essential phenomenon that allows MRI scanners to produce the vast amounts of energy needed to operate effectively.

How LTi went about it

The original joint design was based on a multi-pass, double-sided weld that required a minimum of three passes: a root, a cap, and a second-side cap. To complete the second side, the welder also had to dress the back of the root run, carry out a dye penetrant test to detect surface flaws, and then weld the second side cap. While robust, this process was time-consuming, heavily dependent on manual skill, and difficult to repeat consistently across high volumes.

LTi Metaltech set out to achieve two clear objectives: to develop a single-sided joint that removed the need for dressing and a third pass, and to automate the weld process to deliver consistent, repeatable results. Drawing on its breadth of technical expertise in cryogenic pressure vessel fabrication, LTi redesigned the joint from a double-sided to a single-sided weld that was more cost-effective yet still capable of withstanding the extreme cryogenic conditions required for MRI operation.

This was achieved through several key steps:

  • Design-to-Cost Engineering: A detailed analysis identified an alternative method that increased the material deposition rate, made possible by transitioning from manual TIG welding to automated MAG welding.

  • Robotics and Automation: By adopting robotic welding techniques, LTi introduced greater repeatability, productivity, and cost efficiency, reducing variability and lead times while maintaining compliance.

  • Knowledge Transfer: LTi also shared its expertise with Siemens MRI, helping them embed similar efficiencies into their own production processes for long-term gains.

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What was the outcome?

LTi Metaltech successfully developed and delivered an automated, single-sided welded joint that was fully AD2000 Merkblatt compliant. The new design significantly reduced process times, improved quality consistency, and achieved repeatability at scale - all while withstanding the extreme cryogenic conditions required for MRI cooling systems.

By combining design-to-cost engineering, automation, and compliance, LTi enabled Siemens MRI to achieve faster, more efficient production, while also ensuring uncompromising standards of safety and performance.