Improving Vacuum Integrity in Cryogenic Vessels
A Case Study with Lothar+ and Bolognini Srl
Vacuum-insulated vessels play a critical role in the storage and handling of liquefied gases at cryogenic temperatures. Their thermal performance strongly depends on the quality and long-term stability of the vacuum gap between the inner and outer shells. Even minor vacuum degradation can lead to increased boil-off rates, higher energy consumption and additional costs related to refilling and maintenance.
Over time, cryogenic vessels may require recommissioning processes aimed at restoring vacuum conditions and recovering insulation efficiency. However, vacuum restoration alone is not always sufficient to ensure stable performance in the long term, especially when residual or outgassed impurities are present.
Hydrogen: a critical challenge for vacuum insulation
Among the various impurities released during vessel operation and recommissioning, hydrogen represents the most detrimental contaminant. Due to its high thermal conductivity and extremely low liquefaction temperature, hydrogen cannot be effectively managed through cryo-pumping alone. Even at low concentrations, its presence can significantly compromise the insulating properties of vacuum systems.rnrnTo mitigate these effects, vacuum baking processes are often combined with dedicated hydrogen getters, designed to actively capture hydrogen molecules and stabilize vacuum conditions over time.
The case study: collaboration with Bolognini Srl
In collaboration with Bolognini Srl, a company specialized in the recommissioning of cryogenic storage vessels and gas handling systems, SAES conducted a comparative evaluation of vacuum integrity in cryogenic liquid oxygen (LOX) containers following vacuum restoration.
Twelve identical vessels collected from the field and initially failing the Normal Evaporation Rate (NER) test were included in the study. After standard leak testing and vacuum restoration, the vessels were divided into two groups:
- Group A: vacuum restoration only
- Group B: vacuum restoration combined with the installation of a Lothar+ hydrogen getter, introduced through the vacuum port and positioned on the internal vessel wall prior to evacuation
The NER test, a standardized method used to quantify boil-off mass loss over 24 hours, was selected as a sensitive indicator of vacuum insulation quality.
Results over a 12-month observation period
NER measurements were collected immediately after recommissioning and then repeated after 4 and 12 months. The results highlighted a clear difference between the two groups.
Vessels in Group A, restored without a hydrogen getter, showed increasing variability in NER values over time, indicating higher sensitivity to vacuum degradation. After 12 months, two vessels failed the NER test, with evaporation losses reaching up to 6%.
In contrast, vessels in Group B, equipped with Lothar+, demonstrated stable and uniform NER performance throughout the entire observation period. No vacuum failures were recorded, confirming the effectiveness of the getter in capturing outgassed hydrogen and preserving vacuum integrity.
Read moreConclusions
This case study confirms that vacuum restoration alone may not guarantee long-term thermal stability in cryogenic vacuum-insulated vessels. The integration of SAES Lothar+ hydrogen getter significantly improves vacuum retention, ensuring consistent insulation performance and reducing the risk of early vacuum degradation.
For both newly manufactured and recommissioned cryogenic vessels, the use of Lothar+ represents a practical, low-impact solution to enhance reliability, extend service life and minimize maintenance interventions.
The full Application Note, including test methodology and detailed NER data, is available for download.
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