Trelleborg: Moving LNG Production Offshore Presents Challenges for Industry (USA)

Trelleborg Moving LNG Production Offshore Presents Challenges for Industry

Vincent Lagarrigue, Marketing & Project Manager within Trelleborg Industrial Solutions, presented a white paper at OTC 2013 in Houston.

Moving liquefied natural gas (LNG) production to an offshore setting certainly presents a serious set of challenges for the offshore oil and gas industry, particularly when it comes to the design and construction of a floating offshore gas liquefaction plant (FLNG). This is because FLNG facilities need to maintain the utmost levels of safety and give increased flexibility to LNG production while withstanding the effects of winds, waves and currents in the open seas.

However, with the first FLNG plants now in production, it is safe to say that over the past few years these challenges have been overcome and these facilities have well and truly demonstrated their economic and technical viability to the industry. But while some challenges have certainly been met, others remain.

The environmental conditions of the current FLNG locations are at present quite mild and only require the use of the most straightforward technology for the unloading of the LNG, i.e. marine loading arms. But, with prospective new FLNG locations moving away from these ‘mild’ areas, to sites where sea states, wind and currents can be much more severe, is this straightforward equipment enough?

The full white paper discusses why in these cases, where conditions are much more demanding, conventional marine loading arms will simply not cut it and could result in the shut-down of the liquefaction plant due to bad weather conditions. The paper will outline why tandem offloading solutions, which rely on the use of flexible hoses, are a viable alternative for the industry – not only limiting downtime, but also improving safety.

Demanding Configurations

Not surprisingly, moving LNG production to an offshore setting has presented a demanding set of challenges. However, as well as the design and construction challenges of developing FLNG facilities, extra thought has had to be given to the transfer of the product; LNG transfer must now battle with the effects of winds, waves and currents in the open seas.

Many solutions which could reduce the effect of motion and weather have been considered, however primarily, traditional LNG loading arms have been adapted to enable LNG ship-to-ship transfers in open water through side-by-side configuration. While loading arms can handle both liquids and gases, in a wide range of viscosities and temperatures, environmental constraints, such as the range of tide, wind conditions, and earthquake tolerance can have a significant effect on performance; compared to hoses, loading arms are seen as having a lack of flexibility.

Furthermore, with future FLNG sites being proposed for areas where conditions can be even more extreme, thought has had to be given to more flexible solutions. As such, hose-based solutions for both side-by-side transfers in calmer seas and tandem transfers in rougher conditions are now coming to the forefront as viable alternatives.

Tandem offloading, where vessels line up stern to bow, would allow vessels to keep more distance between them (328 feet / 100 meters distance between FLNG and LNG carriers or more) and more easily cope with greater wave heights. This highly limits the risk of collision between the two vessels, enhancing safety, but also greatly simplifying naval operations in approach, berthing and residence.

[mappress]
LNG World News Staff, May 7, 2013; Image: Trelleborg