Metal treatment – Stock – Ferrous
Reexamination Certificate
1998-06-18
2001-03-20
Wyszomierski, George (Department: 1742)
Metal treatment
Stock
Ferrous
C062S050100, C062S050200, C420S092000, C420S112000, C420S119000
Reexamination Certificate
active
06203631
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to pipe line distribution network systems for transportation of pressurized liquefied natural gas (PLNG), and more particularly, to such systems having pipes and other components that are constructed from an ultra-high strength, low alloy steel containing less than 9 wt % nickel and having a tensile strength greater than 830 MPa (120 ksi) and a DBTT lower than about −73° C. (−100° F.).
BACKGROUND OF THE INVENTION
Various terms are defined in the following specification. For convenience, a Glossary of terms is provided herein, immediately preceding the claims.
Many sources of natural gas are located in remote areas, great distances from any commercial markets for the gas. Sometimes a pipeline is available for transporting produced natural gas to a commercial market. When pipeline transportation to a commercial market is not feasible, produced natural gas is often processed into LNG for transport to market. The LNG is typically transported via specially built tanker ships, and then stored and revaporized at an import terminal near the market. The equipment used to liquefy, transport, store, and revaporize natural gas is generally quite expensive; and a typical conventional LNG project can cost from $5 billion to $10 billion, including field development costs. A typical “grass roots” LNG project requires a minimum natural gas resource of about 280 Gm
3
(10 TCF (trillion cubic feet)) and the LNG customers are generally large utilities. Often, natural gas resources discovered in remote areas are smaller than 280 Gm
3
(10 TCF). Even for natural gas resource bases that meet the 280 Gm
3
(10 TCF) minimum, very long-term commitments of 20 years or more from all involved, i.e., the LNG supplier, the LNG shipper, and the large utility LNG customer, are required to economically process, store, and transport the natural gas as LNG. Where potential LNG customers have an alternative source of gas, such as pipeline gas, the conventional LNG chain of delivery is often not economically competitive.
A conventional LNG plant produces LNG at temperatures of about −162° C. (−260° F.) and at atmospheric pressure. A typical natural gas stream enters a conventional LNG plant at pressures from about 4830 kPa (700 psia) to about 7600 kPa (1100 psia) and temperatures from about 21° C. (70° F.) to about 38° C. (100° F.). Up to about 350,000 refrigeration horsepower are needed to reduce the temperature of the natural gas to the very low outlet temperature of about −162° C. (−260° F.) in a conventional two-train LNG plant. Water, carbon dioxide, sulfur-containing compounds, such as hydrogen sulfide, other acid gases, n-pentane and heavier hydrocarbons, including benzene, must be substantially removed from the natural gas during conventional LNG processing, down to parts-per-million (ppm) levels, or these compounds will freeze, causing plugging problems in the process equipment. In a conventional LNG plant, gas treating equipment is required to remove the carbon dioxide and acid gases. The gas treating equipment typically uses a chemical and/or physical solvent regenerative process and requires a significant capital investment. Also, the operating expenses are high in relation to those for other equipment in the plant. Dry bed dehydrators, such as molecular sieves, are required to remove the water vapor. The scrub column and fractionation equipment are used to remove the hydrocarbons that tend to cause plugging problems. Mercury is also removed in a conventional LNG plant since it can cause failures in equipment constructed of aluminum. In addition, a large portion of the nitrogen that may be present in natural gas is removed after processing since nitrogen will not remain in the liquid phase during transport of conventional LNG and having nitrogen vapors in LNG containers at the point of delivery is undesirable.
Containers, piping, and other equipment used in a conventional LNG plant are typically constructed, at least in part, from aluminum or nickel-containing steel (e.g., 9 wt % nickel), to provide the necessary fracture toughness at the extremely cold processing temperatures. Expensive materials with good fracture toughness at low temperatures, including aluminum and commercial nickel-containing steel (e.g., 9 wt % nickel), are typically used to contain the LNG in the LNG ships and at the import terminals, in addition to their use in the conventional plant.
A typical conventional LNG ship utilizes large spherical containers, known as Moss spheres, to store the LNG during transport. These ships currently cost more than about $230 million each. A typical conventional project to produce LNG in the Middle East and transport it to the Far East night require 7 to 8 of these ships for a total cost of about $1.6 billion to $2.0 billion.
As can be determined from the above discussion, the need exists for a more economical system for processing, storing, and transporting LNG to commercial markets to allow remote natural gas resources to compete more effectively with alternative energy supplies. Furthermore, a system is needed to commercialize smaller remote natural gas resources that would otherwise be uneconomical to develop. In addition, a more economical gasification and distribution system is needed so that LNG can be made economically attractive to smaller consumers.
Consequently, the primary objects of the present invention are to provide a more economical system for processing, storing, and transporting LNG from remote sources to commercial markets and to substantially reduce the threshold size of both the reserve and the market required to make an LNG project economically feasible. One way to accomplish these objects would be to process the LNG at higher pressures and temperatures than is done in a conventional LNG plant, i.e., at pressures higher than atmospheric pressure and temperatures higher than −162° C. (−260° F.). While the general concept of processing, storing, and transporting LNG at increased pressures and temperatures has been discussed in industry publications, these publications generally discuss constructing transportation containers from nickel-containing steel (e.g., 9 wt % nickel) or aluminum, both of which may meet design requirements but are very expensive materials. For example, at pp. 162-164 of his book
NATURAL GAS BY SEA The Development of a New Technology
, published by Witherby & Co. Ltd., first edition 1979, second edition 1993, Roger Ffooks discusses the conversion of the Liberty ship Sigalpha to carry either MLG (medium condition liquefied gas) at 1380 kPa (200 psig) and −115° C. (−175° F.), or CNG (compressed natural gas) processed at 7935 kPa (1150 psig) and −60° C. (−75° F.). Mr. Ffooks indicates that although technically proven, neither of the two concepts found ‘buyers’—largely due to the high cost of storage. According to a paper on the subject referenced by Mr. Ffooks, for CNG service, i.e., at −60° C. (−75° F.), the design target was a low alloy, weldable, quenched and tempered steel with good strength (760 MPa (110 ksi)) and good fracture toughness at operating conditions. (See “A new process for the transportation of natural gas” by R. J. Broeker, International LNG Conference, Chicago, 1968.) This paper also indicates that an aluminum alloy was the lowest cost alloy for MLG service, i.e., at the much lower temperature of −115° C. (−175° F.). Also, Mr. Ffooks discusses, at p. 164, the Ocean Phoenix Transport design, working at a much lower pressure of about 414 kPa (60 psig), with tanks that could be constructed of 9 percent nickel steel or aluminum alloy; and indicates that, again, the concept did not appear to offer sufficient technical or financial advantages to become commercialized. See also: (i) U.S. Pat. No. 3,298,805, which discusses the use of a 9% nickel content steel or a high strength aluminum alloy for making containers for the transport of a compressed natural gas; and (ii) U.S. Pat. No. 4,182,254, whi
Bowen Ronald R.
Minta Moses
Rigby James R.
ExxonMobil Upstream Research Company
Lyles Marcy M.
Wyszomierski George
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