WT Cutts, American Tank & Vessel, Inc., and Eric Reaman, Cashman Preload Cryogenics, USA, explain why full containment LNG storage tanks should be the preferred choice for plant operators over single or double containment alternatives.
With global pressure on petroleum storage, it is as important as ever to make sound, economic choices in LNG/NGL storage selection. Each job and design case are unique, and the overall system needs to be designed for each project. However, on multiple occasions an outer concrete containment structure is a better economic choice and is therefore quickly becoming the preferred standard. More often than not, full containment storage systems are better than single containment or double containment systems, with regards to economics and schedules.
Feed studies lead to full containment
For outer concrete tanks and full containment, historical decisions were driven by issues such as permitting, adjacent fire, local regulations, and other design issues. Today, there is another list of reasons why full containment with an outer concrete tank should be considered for best practice and best economics.
Over the last few years, American Tank & Vessel (AT&V) and Cashman Preload Cryogenics have led multiple projects from the FEED study stage with single containment, only to realise later that full containment offered additional values and a better economic footprint than traditionally understood. Not considering full containment in the FEED study, as well as single containment, can significantly run up costs due to the delays that arise once the benefit and/or necessity of full containment is realised. Therefore, the safe and smart approach is to perform FEED studies based on full containment, with single containment as an option. This process will help avoid many of the extra FEED study costs and delays that have been incurred by several projects in the past.
Outside of traditional considerations, it is important to also consider that full containment tanks have a high integrity design. In the event of an inner tank failure (or an inner tank ‘over-topping’ event) caused by a seismic event or facility malfunction, the concrete outer tank wall is designed to contain both the LNG liquid and vapour, as required by API-625, NFPA 59A, and ACI 376-2011. This benefit provides the facility operator with the comfort of knowing that the entire tank investment is not jeopardised, and that a long shutdown (i.e. multiple years) may be avoided in the aftermath of a single event.
This is an abridged version of an article that was originally published in the June 2020 issue of LNG Industry. The full version can be read here.
Read the article online at: https://www.lngindustry.com/special-reports/23062020/the-economical-choice/