{"title":"Cryogenic Tanks Recertification: Case Study for Operational-Life Extension","authors":"A. Adamou","doi":"10.2118/171998-PA","DOIUrl":null,"url":null,"abstract":"phased structure still has ferrite, but the resulting alloy is ductile enough for static structures such as storage tanks. LNG-storage-tank iron/nickel alloys (9%-nickel alloys are most commonly used), with piping and similar attachments made from austenite stainless steel, have better resistance to thermal fatigue. Corrosion is not a problem at cryogenic temperature, so galvanic coupling between nickel steel and stainless steel is not a source of problems. Austenitic stainless steels at LNG temperatures may be used for building smaller storage tanks, but large containment vessels are usually welded from 9%-nickel steel because of expense considerations. This practice is well-established worldwide (Mokhatab et al. 2014). 3.5%-nickel steel was introduced into cryogenic applications in 1944 for construction of an LNG tank; stainless-steel alloys were scarce because of shortages resulting from World War II. Shortly after going into service, on 20 October 1944, the tank failed. In 1946, investigations by the US Bureau of Mines concluded that the incident was a result of the low-temperature embrittlement of the inner shell of the cylindrical tank. The 3.5%-nickel steel was not used further for cryogenic applications (Mannan 2005). Since 1985, ADGAS has been operating three 80 000-m3, aboveground, double-containment-type tanks, designed according to API Standard 620 (2013), that consist of an inner tank and an outer tank. The inner tank is made of 9%-nickel steel. The outer tank has a post-tensioned concrete wall with a reinforced concrete roof. A secondary bottom is connected to the outer-tank wall to provide a flexible liquid seal. The entire construction is made of 9%-nickel steel. Between 2012 and 2013, a longevity study of the storage and export areas was conducted to ensure their fitness for service up to 2019, as a base case, and 2045, as an extended case. Recertification of “conventional” static equipment, piping, jetty, electrical components, instrumentation, rotating elements, structure, and concrete foundations are not addressed in this paper—only LNG tanks are covered. These tanks have never been inspected internally. The most-important outcome from this study is to advise whether to keep them running beyond their design life or to conduct an intrusive inspection to verify their condition. In this paper, the focus will be given first to the 9%-nickel steel, its properties, and its use in LNG-storage tanks. The different LNGtank design generations and their particularities will be described. A general overview of LNG-tank failures, as recorded in the industry, is presented. Finally, the approach adopted by ADGAS to recertify the LNG tanks is explained. Basically, it is a matter of whether to conduct an intrusive inspection or to keep the tanks operating on the basis of industry practice. For this, well-documented cases will be presented, mainly from Ishikawajima-Harima Heavy Industries, Brunei LNG, Gaz de France, and Malaysia LNG.","PeriodicalId":19446,"journal":{"name":"Oil and gas facilities","volume":"73 1","pages":"88-100"},"PeriodicalIF":0.0000,"publicationDate":"2015-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"1","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Oil and gas facilities","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/10.2118/171998-PA","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
引用次数: 1
Abstract
phased structure still has ferrite, but the resulting alloy is ductile enough for static structures such as storage tanks. LNG-storage-tank iron/nickel alloys (9%-nickel alloys are most commonly used), with piping and similar attachments made from austenite stainless steel, have better resistance to thermal fatigue. Corrosion is not a problem at cryogenic temperature, so galvanic coupling between nickel steel and stainless steel is not a source of problems. Austenitic stainless steels at LNG temperatures may be used for building smaller storage tanks, but large containment vessels are usually welded from 9%-nickel steel because of expense considerations. This practice is well-established worldwide (Mokhatab et al. 2014). 3.5%-nickel steel was introduced into cryogenic applications in 1944 for construction of an LNG tank; stainless-steel alloys were scarce because of shortages resulting from World War II. Shortly after going into service, on 20 October 1944, the tank failed. In 1946, investigations by the US Bureau of Mines concluded that the incident was a result of the low-temperature embrittlement of the inner shell of the cylindrical tank. The 3.5%-nickel steel was not used further for cryogenic applications (Mannan 2005). Since 1985, ADGAS has been operating three 80 000-m3, aboveground, double-containment-type tanks, designed according to API Standard 620 (2013), that consist of an inner tank and an outer tank. The inner tank is made of 9%-nickel steel. The outer tank has a post-tensioned concrete wall with a reinforced concrete roof. A secondary bottom is connected to the outer-tank wall to provide a flexible liquid seal. The entire construction is made of 9%-nickel steel. Between 2012 and 2013, a longevity study of the storage and export areas was conducted to ensure their fitness for service up to 2019, as a base case, and 2045, as an extended case. Recertification of “conventional” static equipment, piping, jetty, electrical components, instrumentation, rotating elements, structure, and concrete foundations are not addressed in this paper—only LNG tanks are covered. These tanks have never been inspected internally. The most-important outcome from this study is to advise whether to keep them running beyond their design life or to conduct an intrusive inspection to verify their condition. In this paper, the focus will be given first to the 9%-nickel steel, its properties, and its use in LNG-storage tanks. The different LNGtank design generations and their particularities will be described. A general overview of LNG-tank failures, as recorded in the industry, is presented. Finally, the approach adopted by ADGAS to recertify the LNG tanks is explained. Basically, it is a matter of whether to conduct an intrusive inspection or to keep the tanks operating on the basis of industry practice. For this, well-documented cases will be presented, mainly from Ishikawajima-Harima Heavy Industries, Brunei LNG, Gaz de France, and Malaysia LNG.