African Fusion March 2017
LNG solutions from Böhler Welding
International Welding Technologist, Marco Engelvaart, Global Industry segment manager for liquefied natural and ethylene gas applications (LNG/LEG) at voestalpine Böhler Welding in Germany, talks about his company’s solutions for cryogenic LNG applications. Welding Solutions for LNG/LEG
L iquefied ethylene (LEG) or meth- ane (LNG) gas is important to the today world’s market. LNG/LEG transport and the number of natural gas processing plants and LNG/LEG terminals are still increasing each year. The present switch to LNG is largely pushed by the low-emission goals in road transportation and industries. Several tests have been run in Western Europe in the use of LNG trucks to deliver their merchandise, which have proved to offer significant advantages, despite the higher investment cost of a LNG-fuelled truck compared to diesel trucks. Advantages for LNG in the trans- port sector are: cleaner fuel with lower CO 2 emission; lower noise; LNG trucks are allowed in city centres; the price of LNG is stable; and, nowadays, LNG is widely available. Cryogenic technology is used to produce LNG, where it is cooled down to -163 °Candcondensed. By cooling to this temperature at atmospheric pressure, natural gas changes into its liquid form.
The volume decreases by 600 times its original volume, making it more attrac- tive for storage and transportation. Many of themajor gas reserves in the world are to be found far away from the end-users. Examples of current locations with large gas-reserves are: Algeria, Aus- tralia, Indonesia, Qatar, Nigeria, Angola, Mozambique; and the shale-gas fields in North America, which is soon to be one of the major global LNG suppliers. Storage tanks for LNG generally have double walls, which have insula- tion between them. The inner wall is principally made of 9% Ni steel. Land- based LNG tanks tend to be cylindrical with a suspended deck. These tanks have been built with a capacity of up to 180 000 m 3 each. The LNG tanks for transport carriers come in different shapes andmaterials. Four types of containment systems are in use for new-build vessels, indepen- dent types A, B and C. Types A and B are the self-supporting (independent) types – Moss (aluminium sphere type)
New floating LNG (FLNG) installations will give access to offshore gas fields that would otherwise have been far too expensive or difficult to develop. Photo courtesy of Shell.
and IHI (prismatic) –while the cylindrical type C uses the shape of the hull of the carrier ship more efficiently (made of 5% Ni Steel for LEG) or 9% Ni steel (for LNG). The remaining type: (integrated) membrane tank types proposed by GTT are manufactured in stainless steel and 36% Ni steel (Invar). Parent metal and welding Especially with regard to toughness requirements at low temperatures, the storage and handling of various liquid gases places great demands on mechanical properties. In general large land-based storage tanks have their inner walls made of steel alloyed with 5-9% nickel. Tanks aboard vessels use a larger variety of alloys, such as aluminium, stainless steel and 5-9% nickel steel. Piping systems and tanks for other transport limit themselves to austenitic stainless steel. Some pipe manufactur- ers produce submerged arc welded 9% Ni pipes using matching consumables. Depending on the final requirement of toughness, these welded pipes need to be heat-treated in order to obtain the specified toughness values. Impact toughness testing (Charpy V) in LNG applications is normally carried out at −196 °C, which can be achieved by cooling down with liquid nitrogen. Apart fromminimum impact toughness at −196 °C, lateral expansion is themost commonly specified requirement for
Horizontal-vertical submerged arc welding of a tank.
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