CA1202578A - Method of prestressing a tubular apparatus - Google Patents
Method of prestressing a tubular apparatusInfo
- Publication number
- CA1202578A CA1202578A CA000435504A CA435504A CA1202578A CA 1202578 A CA1202578 A CA 1202578A CA 000435504 A CA000435504 A CA 000435504A CA 435504 A CA435504 A CA 435504A CA 1202578 A CA1202578 A CA 1202578A
- Authority
- CA
- Canada
- Prior art keywords
- tubular
- tubulars
- yield strength
- prestressing
- stretched
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 238000000034 method Methods 0.000 title claims description 13
- 238000010438 heat treatment Methods 0.000 claims abstract description 12
- 239000000463 material Substances 0.000 claims description 11
- 229910000975 Carbon steel Inorganic materials 0.000 description 6
- 239000010962 carbon steel Substances 0.000 description 6
- 238000004519 manufacturing process Methods 0.000 description 5
- 239000012530 fluid Substances 0.000 description 4
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 4
- 239000003921 oil Substances 0.000 description 4
- 230000006835 compression Effects 0.000 description 3
- 238000007906 compression Methods 0.000 description 3
- 239000007789 gas Substances 0.000 description 3
- 238000009413 insulation Methods 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- RTZKZFJDLAIYFH-UHFFFAOYSA-N Diethyl ether Chemical compound CCOCC RTZKZFJDLAIYFH-UHFFFAOYSA-N 0.000 description 2
- 238000010793 Steam injection (oil industry) Methods 0.000 description 2
- 229910000831 Steel Inorganic materials 0.000 description 2
- 238000001816 cooling Methods 0.000 description 2
- 239000013256 coordination polymer Substances 0.000 description 2
- 230000007797 corrosion Effects 0.000 description 2
- 238000005260 corrosion Methods 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 238000002347 injection Methods 0.000 description 2
- 239000007924 injection Substances 0.000 description 2
- 150000002500 ions Chemical class 0.000 description 2
- 239000003345 natural gas Substances 0.000 description 2
- 239000010959 steel Substances 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 1
- 241000490229 Eucephalus Species 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- 238000010795 Steam Flooding Methods 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 230000004888 barrier function Effects 0.000 description 1
- 229910002091 carbon monoxide Inorganic materials 0.000 description 1
- 239000010779 crude oil Substances 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000000835 fiber Substances 0.000 description 1
- 239000000295 fuel oil Substances 0.000 description 1
- 229930195733 hydrocarbon Natural products 0.000 description 1
- 150000002430 hydrocarbons Chemical class 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- MWUXSHHQAYIFBG-UHFFFAOYSA-N nitrogen oxide Inorganic materials O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 1
- 239000003129 oil well Substances 0.000 description 1
- 230000002035 prolonged effect Effects 0.000 description 1
- 239000011435 rock Substances 0.000 description 1
- 230000000638 stimulation Effects 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21D41/00—Application of procedures in order to alter the diameter of tube ends
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B17/00—Drilling rods or pipes; Flexible drill strings; Kellies; Drill collars; Sucker rods; Cables; Casings; Tubings
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21C—MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES OR PROFILES, OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
- B21C37/00—Manufacture of metal sheets, bars, wire, tubes or like semi-manufactured products, not otherwise provided for; Manufacture of tubes of special shape
- B21C37/06—Manufacture of metal sheets, bars, wire, tubes or like semi-manufactured products, not otherwise provided for; Manufacture of tubes of special shape of tubes or metal hoses; Combined procedures for making tubes, e.g. for making multi-wall tubes
- B21C37/15—Making tubes of special shape; Making tube fittings
- B21C37/154—Making multi-wall tubes
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21C—MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES OR PROFILES, OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
- B21C37/00—Manufacture of metal sheets, bars, wire, tubes or like semi-manufactured products, not otherwise provided for; Manufacture of tubes of special shape
- B21C37/06—Manufacture of metal sheets, bars, wire, tubes or like semi-manufactured products, not otherwise provided for; Manufacture of tubes of special shape of tubes or metal hoses; Combined procedures for making tubes, e.g. for making multi-wall tubes
- B21C37/15—Making tubes of special shape; Making tube fittings
- B21C37/20—Making helical or similar guides in or on tubes without removing material, e.g. by drawing same over mandrels, by pushing same through dies ; Making tubes with angled walls, ribbed tubes and tubes with decorated walls
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B36/00—Heating, cooling or insulating arrangements for boreholes or wells, e.g. for use in permafrost zones
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B36/00—Heating, cooling or insulating arrangements for boreholes or wells, e.g. for use in permafrost zones
- E21B36/003—Insulating arrangements
Landscapes
- Engineering & Computer Science (AREA)
- Life Sciences & Earth Sciences (AREA)
- Geology (AREA)
- Mining & Mineral Resources (AREA)
- Mechanical Engineering (AREA)
- Physics & Mathematics (AREA)
- Chemical & Material Sciences (AREA)
- Environmental & Geological Engineering (AREA)
- Fluid Mechanics (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Geochemistry & Mineralogy (AREA)
- Crystallography & Structural Chemistry (AREA)
- Thermal Sciences (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Rigid Pipes And Flexible Pipes (AREA)
- Meat, Egg Or Seafood Products (AREA)
- Thermal Insulation (AREA)
- Shaping By String And By Release Of Stress In Plastics And The Like (AREA)
- Processing Of Meat And Fish (AREA)
- Earth Drilling (AREA)
- Packages (AREA)
- Heat Treatment Of Articles (AREA)
- Load-Engaging Elements For Cranes (AREA)
- Supports For Pipes And Cables (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A tubular apparatus is assembled of inner and outer tubes which are connected at spaced locations along their length. After heat treatment and other processing steps, either the inner or outer tube is heated to reduce its yield strength and then stretched beyond its yield point but not beyond the yield point of the other tubular. The heat source is removed so that the stretched state is maintained. The tubular apparatus is thus prestressed with the inner tube under compressive prestressing when the inner tube has been heated and stretched, and the inner tube under tensile prestressing when the outer tube hasbeen heated and stretched.
A tubular apparatus is assembled of inner and outer tubes which are connected at spaced locations along their length. After heat treatment and other processing steps, either the inner or outer tube is heated to reduce its yield strength and then stretched beyond its yield point but not beyond the yield point of the other tubular. The heat source is removed so that the stretched state is maintained. The tubular apparatus is thus prestressed with the inner tube under compressive prestressing when the inner tube has been heated and stretched, and the inner tube under tensile prestressing when the outer tube hasbeen heated and stretched.
Description
~25~7~
C:ASE ~497 ME1~ OF P~RL:SllR~SING A TUBULAR APP~RA~U5 l~lEI D ~WD B~KGROUND OF THE INVENTION
The present invention relates, in general~ to the prestressing of elongated conduits îor conveying hot or cold fluid, and in particular to a new and useful method of manufacturing and prestressing tubular apparatus made of two or more coaxial tubes.
Heavy oil and tar sands represent huge untapped resources o E liquid hydrocarbons which will be produced in increasing quantities ~o help supplernentdeclining production of conventional crude oil. These deposits must9 however, be heated to reduce the oil viscosity before i~ will flow to the producing wellsin economical quantities. A dominant method of heating is by injection of surface generated steam in either a continuous (steam flood) or intermittent ~steam stimulation or "huEf and puff") mode.
When steam is injected down long injection pipes or "stringsl', a significant amount o thermal energy is lost to the rock overburden (500 ~o 7,000 feet) which covers the oil deposit. In the initial steam injection projects, the price oE
oil did not justify the preYention of this heat loss, but now with the price of oil ~ $3Q or more a barrel, insulation systerns for the well iniection pipe become economically justified.
Thermally insulated double wall piping structures are known and used7 for example, as insulated steam injection tubing in oil wells, or in plpe lines for carrying fluids at elevated tempera~ures~ Such piping is disclosed, for example,in U.S. Patent No. 3,574,357 to Alexandru et al and U.S. Paten~ No. 3,397,745 to Owens et al.
It is cotnmon practice for such tubes to be prestressed in order to compensate for diiEEerential expansion of the inner and outer coaxial walls or tubes. Such prestressing is done, for example) by elongating the inner tube through such means as heating or mechanically stretching and attaching the outer tube while the inner hlbe is in such an elongated state. While still held in the elongated state, any heat treatment required for the attachment is ~, ~
s~
CP~SE ~4~7 completed. However, it is difficult to heat trea~ the welds while the tubes are under stress. For ~his reason, it is believed that such heat ~rea~ment of the welds is not normally dcne in the industry~ resulting in welds which are more brittle, rnore damage prone, and more corrosion prone.
After cool down of the heat ~reatmen~, if any, the heating or mechanical stretching is then removed anci the tubes assume a state of tensile prestress onthe inner ~ube and compressive prestress on the outer tube. While in service, the inner tube ~ecomes hot and expandsO ll~is relaxes the tensile prestress before the inner tube goes into compression. ~ this manner, the inner ~ube is prevented from buckling.
In an analsgous fashiol-, where the inner tube is adapted to convey cold fluids, the outer tube is hea~ed or mechanically stretched before the inner tubeis connected thereto.
Disadvantages of these prior approaches to prestressing double walled tubes or conduits is that ~he inner, outer, or both tubes must be held in their compressed or stretched sta~e while other manuf ac~using steps are accomplished such as the connection of the tubes, the heat ~re~tment thereof and the cool-down therefrom.
SUMMAI~Y S )F l HE INVEN llON
According to the present invention, a desired state of prestress is establlshed in a double wall tubing structure, while difficulties and disadvan~ages of the prior ar~ methods are avoided.
According to the method of this invention~ the tubes or pipes are assembled and fixedly joined to each other without prestressing. Any required heat treatmen~ of the struc~ure or the joint is then performed again without any prestress condition. 1~ achieve a prestress, the outer tube member is locally heated to reduce its yield strength and then is mechanically stressed beyond its yield strength. The hea~ source is removed so that the mechanical stretching is rendered permanent. The outer tube portion is thus plastically deformed while the inner tube portion remains elastic. After cooling, the load
C:ASE ~497 ME1~ OF P~RL:SllR~SING A TUBULAR APP~RA~U5 l~lEI D ~WD B~KGROUND OF THE INVENTION
The present invention relates, in general~ to the prestressing of elongated conduits îor conveying hot or cold fluid, and in particular to a new and useful method of manufacturing and prestressing tubular apparatus made of two or more coaxial tubes.
Heavy oil and tar sands represent huge untapped resources o E liquid hydrocarbons which will be produced in increasing quantities ~o help supplernentdeclining production of conventional crude oil. These deposits must9 however, be heated to reduce the oil viscosity before i~ will flow to the producing wellsin economical quantities. A dominant method of heating is by injection of surface generated steam in either a continuous (steam flood) or intermittent ~steam stimulation or "huEf and puff") mode.
When steam is injected down long injection pipes or "stringsl', a significant amount o thermal energy is lost to the rock overburden (500 ~o 7,000 feet) which covers the oil deposit. In the initial steam injection projects, the price oE
oil did not justify the preYention of this heat loss, but now with the price of oil ~ $3Q or more a barrel, insulation systerns for the well iniection pipe become economically justified.
Thermally insulated double wall piping structures are known and used7 for example, as insulated steam injection tubing in oil wells, or in plpe lines for carrying fluids at elevated tempera~ures~ Such piping is disclosed, for example,in U.S. Patent No. 3,574,357 to Alexandru et al and U.S. Paten~ No. 3,397,745 to Owens et al.
It is cotnmon practice for such tubes to be prestressed in order to compensate for diiEEerential expansion of the inner and outer coaxial walls or tubes. Such prestressing is done, for example) by elongating the inner tube through such means as heating or mechanically stretching and attaching the outer tube while the inner hlbe is in such an elongated state. While still held in the elongated state, any heat treatment required for the attachment is ~, ~
s~
CP~SE ~4~7 completed. However, it is difficult to heat trea~ the welds while the tubes are under stress. For ~his reason, it is believed that such heat ~rea~ment of the welds is not normally dcne in the industry~ resulting in welds which are more brittle, rnore damage prone, and more corrosion prone.
After cool down of the heat ~reatmen~, if any, the heating or mechanical stretching is then removed anci the tubes assume a state of tensile prestress onthe inner ~ube and compressive prestress on the outer tube. While in service, the inner tube ~ecomes hot and expandsO ll~is relaxes the tensile prestress before the inner tube goes into compression. ~ this manner, the inner ~ube is prevented from buckling.
In an analsgous fashiol-, where the inner tube is adapted to convey cold fluids, the outer tube is hea~ed or mechanically stretched before the inner tubeis connected thereto.
Disadvantages of these prior approaches to prestressing double walled tubes or conduits is that ~he inner, outer, or both tubes must be held in their compressed or stretched sta~e while other manuf ac~using steps are accomplished such as the connection of the tubes, the heat ~re~tment thereof and the cool-down therefrom.
SUMMAI~Y S )F l HE INVEN llON
According to the present invention, a desired state of prestress is establlshed in a double wall tubing structure, while difficulties and disadvan~ages of the prior ar~ methods are avoided.
According to the method of this invention~ the tubes or pipes are assembled and fixedly joined to each other without prestressing. Any required heat treatmen~ of the struc~ure or the joint is then performed again without any prestress condition. 1~ achieve a prestress, the outer tube member is locally heated to reduce its yield strength and then is mechanically stressed beyond its yield strength. The hea~ source is removed so that the mechanical stretching is rendered permanent. The outer tube portion is thus plastically deformed while the inner tube portion remains elastic. After cooling, the load
-2-æs~7~
CAS~ ~497 estabiishing the mechanical stretching can be removed. Opon complete cooling, the desired prestress condltion is present with a tensile force on the inner tube and a compressive force on the outer tube.
This structure is useful in conveying hot fluids such as steam in the inner tube portion.
Where cold 1uids are to be conveyed9 such as llquefied natural gas, it is desirable ~o have a tensile prestressing on ~he outer tube and a compressive prestressing on the inner tube. This is achieved according to -the imention by heating at leas~ a portion of the inner tube to reduce its yield strength and mechanically stressing the inner tube beyorld its yield strength. The heat source is ~hen remoYed. llle inner tube portion is thus plastically deformed while the outer tube portion remaîns elastic.
The present invention eliminates the need to maintain ~he elongation of one tube relative to the other tube while joining them to~ether or the need to maintain such elongation while performing heat treatment operations~ is simplîfies these operations and reduces their cos~, especîally since heat treatment of the members connecting the tubulars is very difficult to perform while the tubulars are in a prestressed condition. This method permits the prestressing to be performed at a convenient time in the production sequence 2Q and after any operations which may produce rejectable parts. Thus9 th prestressing steps are achieYed only after all previous steps have been accomplished satisf actorily. This results in a f aster and less expensive production sequence and decreases the production investment in rejectable parts.
Accordingly, another object of the lnvention is to provide a method of prestressing a double wall tube having an inner tubular and an outer tubular connected to thc inner tubular at at least two spaced locations along their length, comprising, heating at least a portion of one of the inner and outer tubulars sufficiently to reduce the yield strength thereof, mechanically stretching said one of the inner and outer tubulars to elongate said one of t inner ~nd outer hlbulars by a selected amount, and permitting said one of the
CAS~ ~497 estabiishing the mechanical stretching can be removed. Opon complete cooling, the desired prestress condltion is present with a tensile force on the inner tube and a compressive force on the outer tube.
This structure is useful in conveying hot fluids such as steam in the inner tube portion.
Where cold 1uids are to be conveyed9 such as llquefied natural gas, it is desirable ~o have a tensile prestressing on ~he outer tube and a compressive prestressing on the inner tube. This is achieved according to -the imention by heating at leas~ a portion of the inner tube to reduce its yield strength and mechanically stressing the inner tube beyorld its yield strength. The heat source is ~hen remoYed. llle inner tube portion is thus plastically deformed while the outer tube portion remaîns elastic.
The present invention eliminates the need to maintain ~he elongation of one tube relative to the other tube while joining them to~ether or the need to maintain such elongation while performing heat treatment operations~ is simplîfies these operations and reduces their cos~, especîally since heat treatment of the members connecting the tubulars is very difficult to perform while the tubulars are in a prestressed condition. This method permits the prestressing to be performed at a convenient time in the production sequence 2Q and after any operations which may produce rejectable parts. Thus9 th prestressing steps are achieYed only after all previous steps have been accomplished satisf actorily. This results in a f aster and less expensive production sequence and decreases the production investment in rejectable parts.
Accordingly, another object of the lnvention is to provide a method of prestressing a double wall tube having an inner tubular and an outer tubular connected to thc inner tubular at at least two spaced locations along their length, comprising, heating at least a portion of one of the inner and outer tubulars sufficiently to reduce the yield strength thereof, mechanically stretching said one of the inner and outer tubulars to elongate said one of t inner ~nd outer hlbulars by a selected amount, and permitting said one of the
3-CASE 4~g7 inner and outer tubulars to cool.
A still further object of the invention is to provide a method of manufac~urin~ a prestressed double wall tube having an inner tubular connected to an outer tubular at at leas~ two spaced locations along ~heir length eomprising, providing the inner tubular with a material having a different yieldstren~th than the outer tubular and stre~ching the tubular which has a lower yield strength pas~ its yield but not stretching the ~ubular which has the higher yield strength past its yield point ~o prestress the double wall tube.
The v~rious fe~tures of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part oE
this disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its uses, reference is made ~o the accompanying drawings and descrip~ive matter in which preferred embodiments ~f the invention are illustrated.
BlRIEF DESCRIP11(9N OF THlE DlE~AWlNGS
In the Drawings:
Fig. 1 is a side sectional view of a double wall $ube according to the invention showing at the top half an unstressed condition and at the bottom halfa prestressed condition;
Flg. 2 is a graph showing the relationship between stresses in the outer and inner tubulars after prestressing due ~o an externally applied force;
~ig. 3 is a graph showing the yield strength of a typical carbon steel~
versus temperature;
Fig. 4 is a graph showing the stress in the inner tubular as it relates to the stress in ~he heated outer tubular during the prestressing process;
Fig. 5 is a graph showing the relationship between stress and strain for a typical carbon steel at ll00 degrees F; and Fig. 6 is a graph relating the plastic (heated) length of the outer ~ubular to the plastic strain needed for a given total elongation.
a~ ~
25~3 CAS~ l~h,g7 DE5;:RIPIION OF TH~ PREFERRI~D EUB~DI-UENTS
~eferrin8 to the drawings in particular9 the invention embodied therein comprises a method of prestressing a double wall tube generally designated 10 in Fig. 1, which comprises an outer tubular 12 and an inner tubular 14 which are connected to each other at axially spaced joints 16 and 18, which are preferably at or near the ends of t~bulars 12, 14.
l?le upper half ~f ~ig. 1 shows the double wall tube before it is prestressed. ~ the embodiment shown, the length l o is chosen to be 40 eet and the material, at las~ of the outer tubular, is chosen to be carbon steel~
171e lower half of Fig. 1 shows the stretched and prestressed state of double wall tube 10. The length has been increased by an arnount ~\~ L~
For this exarnple, suppose that the tubulars are chosen to be:
Outer tubular: 40 ft. long 4S~" OD
.271" wall carbon steel 55 K~I room temperature yield s~reng~h Area of cross section = 3.600 in2 Inner tubular- 40 ~eet long 2-7/8l' OD
.217" wall carbon steel 80 KSI room tempera~ure yield strength Area 3f cross section = 1.812 in2;
and that the desired level of prestress in the inner tubular is 25 KSI (tension~.
~t isothermal conditions (same temperature on both tubes), the corresponding stress in the outer tubular is 12.6 KSI compression.
The inner tubular is inser~ed into the o~er tubular, the tubes are welded together at each end with no prestress and the welds are heat-treated as required.
257~3 CAS~ 4~7 lo produce the desired condition of prestress, the outer tube is first heated to 1100F over a length of 12 inches. A typical stress-strain curve for acarbon steel at this ternperature is shown in Figure 5. Both tubes are then subjected to a load of 271.8 Kips (~housand pounds). This load produces a stressin the inner tube of 75 KSI tension (elastic~ and in the outer tube of 37.75 KSItension. In the heated portion of the outer tube7 this stress produces 5% plastic strain, while in the cooler portion3 the s~ress is still elastic. llle 5% piastic strain oYer a 12 inch length results in a total overall length increase of 6 inch.
When the outer tube cools to about 80ûF, the load is removed. When the outer tube has cooled to room temperature, the ~6 inch length increase results in the desired stress state: 25 KSI tension in the inner tube, 12.6 KSI compression in the outer tube.
~ its prestressed condition, the inner tubular thus is exposed to an incremental stress ~ OI 25 KSI. Factoring in the dif Eerence in area of the inner ~5 and outer tubulars, this corresponds to a compressive stress on the outer tubular of ~ = 12.6 KSI.
Fig. 2 shows the relationship between the incremental stresses on the inner and outer tubulars with a maximum on the outer tubular being 37.5 KSI.
This maximum level is established since above this level the yield strength for the inner tubular is approached.
Fi8. 3 shows the relationship between tempera~ure in degrees Fahrenheit and yield streng~h for a typical carbon steel used for the outer tubular (e.g. 8260 annealed steel). ln order to reduce the yield strength to less than 37.5 KSI, a temperature of at least about 1000 degrees F is reguired. ~ fact, the yield strength must be somewhat lower since the outer tube rnust not only yield but itmust also undergo sorne ~train.
Fig. 4 illustrates how the Eorce applied to the outer tubular initially effects a linear increase in length. Once the yield point is reached for the outer tubular, however, the increase becomes non-linear and corresponds to plastic deformation of the outer tubular. With a release of the load, ~he prestress on the inner tubular decreases until it reaches the desired level of 25 ` :.
~2~713 CASE ~497 lCSI. This is a condition which is in e~uilibrium with the 12.6 KSI compressive prestress on the outer tukular.
13y selecting the temperature and the heated length for the outer tubular, the prestress on the inner tubular ~an be controlled The stress ~strain state) at the completion of yielding must fall on ~he curve shown in Fig. 2. Once the stress-strain curve for the outer tubular is known, the hea~ed len~th can be determined as can the temperature of the opera~ion.
As long as the tempera~ure is such that the minimum yield of the outer tube is greater than 12.6 KSI, i~ is probably not necessary to hold the prest~ess once the yielding has occurred. l~is is ~ssuming that the hea~ed length is shortenough so as not to buckle.
The required plastic deformation (~L~ is about 0.6 inches with the plastic strain needed as a ~unc~ion of the heated length being shown in Fig. 6.
llle double wall tube described above is useful where the inner ~ube is intended to convey heat~d substances such as steam. Where the inner tube is intended to convey cold substances such as liqueEled natural gas, the inner tuberather than the outer tube can be heated and stretched.
As an alternate measure, ~he material making up the inner and outer tubulars can be chosen to have different yield strengths, with the member to be plastically deformed having the lower yield strength.
It is noted that two or more inner tubes may be provided within the outer tube and may be prestressed to different levels. This is possible by providing the tubes with diferent yield strengths. The inner tubes may be axially spaced and aligned, disposed one next to the other or one within the other.
It is also advantageous to insulate the annular space forrned between the inner and outer tubes. This can be done by providing fibers or layered insulation which is preferably wrapped around the inner tube. A thermal barrier can also be established by e~racuating the annular space. The evacuated space may be used in conjunction with the fibrous or layered insulation, or alone. To maintain the vacuum over a prolonged period of use for the tubing, a getter material is provided, preferably at a high temperature location within the annular space9 , ~2578 CP~SE 4497 that absorbs such gases. Such a getter material is preferably adjacent the innertube and activatable at a temperature between 400 and 700F. Gases which may leak in~o the vacuum include hydrogen formed by corrosion on the outer tube migrating through the outer tube and such gases as nitrogen and carbon monoxide outgassed from ~he material of the inner tube.
~ an alternative embodimen~ of this invention, the inner ~ubular 14 is composed of a material which has a higher yield s~reng~h than the material of the outer tubular, and the stress in the inner tubular 14 is allowed to exceed its yield strength while the outer tubular 12 is stretched such ~hat its yield strength is exceeded. This results in a prestressed condition which is limited by the difference in the yield strengths of the tubulars.
While a specific em~odiment of the invention has been shown and descri~ed in detall to illus trate the application of the principles of the inYention, It will be understood that the inYention may be embodied otherwise without departing from sueh principles.
..,
A still further object of the invention is to provide a method of manufac~urin~ a prestressed double wall tube having an inner tubular connected to an outer tubular at at leas~ two spaced locations along ~heir length eomprising, providing the inner tubular with a material having a different yieldstren~th than the outer tubular and stre~ching the tubular which has a lower yield strength pas~ its yield but not stretching the ~ubular which has the higher yield strength past its yield point ~o prestress the double wall tube.
The v~rious fe~tures of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part oE
this disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its uses, reference is made ~o the accompanying drawings and descrip~ive matter in which preferred embodiments ~f the invention are illustrated.
BlRIEF DESCRIP11(9N OF THlE DlE~AWlNGS
In the Drawings:
Fig. 1 is a side sectional view of a double wall $ube according to the invention showing at the top half an unstressed condition and at the bottom halfa prestressed condition;
Flg. 2 is a graph showing the relationship between stresses in the outer and inner tubulars after prestressing due ~o an externally applied force;
~ig. 3 is a graph showing the yield strength of a typical carbon steel~
versus temperature;
Fig. 4 is a graph showing the stress in the inner tubular as it relates to the stress in ~he heated outer tubular during the prestressing process;
Fig. 5 is a graph showing the relationship between stress and strain for a typical carbon steel at ll00 degrees F; and Fig. 6 is a graph relating the plastic (heated) length of the outer ~ubular to the plastic strain needed for a given total elongation.
a~ ~
25~3 CAS~ l~h,g7 DE5;:RIPIION OF TH~ PREFERRI~D EUB~DI-UENTS
~eferrin8 to the drawings in particular9 the invention embodied therein comprises a method of prestressing a double wall tube generally designated 10 in Fig. 1, which comprises an outer tubular 12 and an inner tubular 14 which are connected to each other at axially spaced joints 16 and 18, which are preferably at or near the ends of t~bulars 12, 14.
l?le upper half ~f ~ig. 1 shows the double wall tube before it is prestressed. ~ the embodiment shown, the length l o is chosen to be 40 eet and the material, at las~ of the outer tubular, is chosen to be carbon steel~
171e lower half of Fig. 1 shows the stretched and prestressed state of double wall tube 10. The length has been increased by an arnount ~\~ L~
For this exarnple, suppose that the tubulars are chosen to be:
Outer tubular: 40 ft. long 4S~" OD
.271" wall carbon steel 55 K~I room temperature yield s~reng~h Area of cross section = 3.600 in2 Inner tubular- 40 ~eet long 2-7/8l' OD
.217" wall carbon steel 80 KSI room tempera~ure yield strength Area 3f cross section = 1.812 in2;
and that the desired level of prestress in the inner tubular is 25 KSI (tension~.
~t isothermal conditions (same temperature on both tubes), the corresponding stress in the outer tubular is 12.6 KSI compression.
The inner tubular is inser~ed into the o~er tubular, the tubes are welded together at each end with no prestress and the welds are heat-treated as required.
257~3 CAS~ 4~7 lo produce the desired condition of prestress, the outer tube is first heated to 1100F over a length of 12 inches. A typical stress-strain curve for acarbon steel at this ternperature is shown in Figure 5. Both tubes are then subjected to a load of 271.8 Kips (~housand pounds). This load produces a stressin the inner tube of 75 KSI tension (elastic~ and in the outer tube of 37.75 KSItension. In the heated portion of the outer tube7 this stress produces 5% plastic strain, while in the cooler portion3 the s~ress is still elastic. llle 5% piastic strain oYer a 12 inch length results in a total overall length increase of 6 inch.
When the outer tube cools to about 80ûF, the load is removed. When the outer tube has cooled to room temperature, the ~6 inch length increase results in the desired stress state: 25 KSI tension in the inner tube, 12.6 KSI compression in the outer tube.
~ its prestressed condition, the inner tubular thus is exposed to an incremental stress ~ OI 25 KSI. Factoring in the dif Eerence in area of the inner ~5 and outer tubulars, this corresponds to a compressive stress on the outer tubular of ~ = 12.6 KSI.
Fig. 2 shows the relationship between the incremental stresses on the inner and outer tubulars with a maximum on the outer tubular being 37.5 KSI.
This maximum level is established since above this level the yield strength for the inner tubular is approached.
Fi8. 3 shows the relationship between tempera~ure in degrees Fahrenheit and yield streng~h for a typical carbon steel used for the outer tubular (e.g. 8260 annealed steel). ln order to reduce the yield strength to less than 37.5 KSI, a temperature of at least about 1000 degrees F is reguired. ~ fact, the yield strength must be somewhat lower since the outer tube rnust not only yield but itmust also undergo sorne ~train.
Fig. 4 illustrates how the Eorce applied to the outer tubular initially effects a linear increase in length. Once the yield point is reached for the outer tubular, however, the increase becomes non-linear and corresponds to plastic deformation of the outer tubular. With a release of the load, ~he prestress on the inner tubular decreases until it reaches the desired level of 25 ` :.
~2~713 CASE ~497 lCSI. This is a condition which is in e~uilibrium with the 12.6 KSI compressive prestress on the outer tukular.
13y selecting the temperature and the heated length for the outer tubular, the prestress on the inner tubular ~an be controlled The stress ~strain state) at the completion of yielding must fall on ~he curve shown in Fig. 2. Once the stress-strain curve for the outer tubular is known, the hea~ed len~th can be determined as can the temperature of the opera~ion.
As long as the tempera~ure is such that the minimum yield of the outer tube is greater than 12.6 KSI, i~ is probably not necessary to hold the prest~ess once the yielding has occurred. l~is is ~ssuming that the hea~ed length is shortenough so as not to buckle.
The required plastic deformation (~L~ is about 0.6 inches with the plastic strain needed as a ~unc~ion of the heated length being shown in Fig. 6.
llle double wall tube described above is useful where the inner ~ube is intended to convey heat~d substances such as steam. Where the inner tube is intended to convey cold substances such as liqueEled natural gas, the inner tuberather than the outer tube can be heated and stretched.
As an alternate measure, ~he material making up the inner and outer tubulars can be chosen to have different yield strengths, with the member to be plastically deformed having the lower yield strength.
It is noted that two or more inner tubes may be provided within the outer tube and may be prestressed to different levels. This is possible by providing the tubes with diferent yield strengths. The inner tubes may be axially spaced and aligned, disposed one next to the other or one within the other.
It is also advantageous to insulate the annular space forrned between the inner and outer tubes. This can be done by providing fibers or layered insulation which is preferably wrapped around the inner tube. A thermal barrier can also be established by e~racuating the annular space. The evacuated space may be used in conjunction with the fibrous or layered insulation, or alone. To maintain the vacuum over a prolonged period of use for the tubing, a getter material is provided, preferably at a high temperature location within the annular space9 , ~2578 CP~SE 4497 that absorbs such gases. Such a getter material is preferably adjacent the innertube and activatable at a temperature between 400 and 700F. Gases which may leak in~o the vacuum include hydrogen formed by corrosion on the outer tube migrating through the outer tube and such gases as nitrogen and carbon monoxide outgassed from ~he material of the inner tube.
~ an alternative embodimen~ of this invention, the inner ~ubular 14 is composed of a material which has a higher yield s~reng~h than the material of the outer tubular, and the stress in the inner tubular 14 is allowed to exceed its yield strength while the outer tubular 12 is stretched such ~hat its yield strength is exceeded. This results in a prestressed condition which is limited by the difference in the yield strengths of the tubulars.
While a specific em~odiment of the invention has been shown and descri~ed in detall to illus trate the application of the principles of the inYention, It will be understood that the inYention may be embodied otherwise without departing from sueh principles.
..,
Claims (5)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of prestressing tubular apparatus having at least one inner tubular and an outer tubular connected to the inner tubular at at least two spaced locations along the length thereof, comprising:
heating at least a portion of one of the inner and outer tubulars to a temperature sufficient for reducing the yield strength of said portion of said one of the inner and outer tubulars to a yield strength which is less than the yield strength of the other of the inner and outer tubulars;
stretching the inner and outer tubulars by a selected amount which is beyond the yield point of said one tubular and which is not beyond the yield point of said other tubular; and permitting said one of the inner and outer tubulars to cool while said tubulars are stretched whereby the double wall tube is prestressed.
heating at least a portion of one of the inner and outer tubulars to a temperature sufficient for reducing the yield strength of said portion of said one of the inner and outer tubulars to a yield strength which is less than the yield strength of the other of the inner and outer tubulars;
stretching the inner and outer tubulars by a selected amount which is beyond the yield point of said one tubular and which is not beyond the yield point of said other tubular; and permitting said one of the inner and outer tubulars to cool while said tubulars are stretched whereby the double wall tube is prestressed.
2. A method according to claim 1, including heating and mechanically stretching the outer tubular so as to apply a compressive prestressing thereto and so as to apply a tensile prestressing to the inner tubular.
3. A method according to claim 1, including heating and stretching the inner tubular so as to apply a compressive prestressing thereto and so as to apply tensile prestressing to the outer tubular.
4. A method of prestressing a tubular apparatus having at least one inner tubular and an outer tubular connected to the inner tubular at two spaced locations along the length thereof, comprising:
providing the inner and outer tubulars of materials having different yield strengths and mechanically stretching the inner and outer tubulars so that the tubular having the lower yield strength is stretched beyond its lower yield strength.
providing the inner and outer tubulars of materials having different yield strengths and mechanically stretching the inner and outer tubulars so that the tubular having the lower yield strength is stretched beyond its lower yield strength.
5. A prestressed tubular apparatus comprising:
at least one inner tubular made of material having a first yield strength;
an outer tubular positioned around said inner tubular and made of a material having a second yield strength;
at least two joints mechanically connecting said inner and outer tubulars at spaced locations along the length thereof; and said first and second tubulars being in a stretched state sufficient to have plastically deformed the one of said inner and outer tubulars having a lower yield strength but not to have plastically deformed the other of said inner and outer tubulars having a higher yield strength.
at least one inner tubular made of material having a first yield strength;
an outer tubular positioned around said inner tubular and made of a material having a second yield strength;
at least two joints mechanically connecting said inner and outer tubulars at spaced locations along the length thereof; and said first and second tubulars being in a stretched state sufficient to have plastically deformed the one of said inner and outer tubulars having a lower yield strength but not to have plastically deformed the other of said inner and outer tubulars having a higher yield strength.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US41329082A | 1982-08-31 | 1982-08-31 | |
| US413,290 | 1982-08-31 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1202578A true CA1202578A (en) | 1986-04-01 |
Family
ID=23636667
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000435504A Expired CA1202578A (en) | 1982-08-31 | 1983-08-26 | Method of prestressing a tubular apparatus |
Country Status (10)
| Country | Link |
|---|---|
| EP (1) | EP0104789B1 (en) |
| JP (1) | JPS6018877B2 (en) |
| KR (1) | KR840005678A (en) |
| AT (1) | ATE23461T1 (en) |
| BR (1) | BR8304591A (en) |
| CA (1) | CA1202578A (en) |
| DE (1) | DE3367539D1 (en) |
| IN (1) | IN162701B (en) |
| PH (1) | PH20499A (en) |
| TR (1) | TR21779A (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0192785A1 (en) * | 1985-01-31 | 1986-09-03 | Bruno Dipl.-Ing. Zay | Process for industrially making prestressed and pre-insulated sleeves for pipes |
| DE3605039A1 (en) * | 1986-02-18 | 1986-12-11 | Zay, Bruno, Dipl.-Ing., 4030 Ratingen | METHOD FOR THE PRODUCTION OF STEEL SHEATHING SHEETS AND THEIR LAYING IN PLASTIC SHEATHING TUBE SYSTEMS |
| RU2707768C1 (en) * | 2018-12-05 | 2019-11-29 | Акционерное общество "Уральский научно-технологический комплекс" | Method of applying polyurethane coating on fuel tanks |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3511282A (en) * | 1966-02-07 | 1970-05-12 | Continental Oil Co | Prestressed conduit for heated fluids |
| US3397745A (en) * | 1966-03-08 | 1968-08-20 | Carl Owens | Vacuum-insulated steam-injection system for oil wells |
| US3574357A (en) * | 1969-02-27 | 1971-04-13 | Grupul Ind Pentru Foray Si Ext | Thermal insulating tubing |
| US3693665A (en) * | 1970-01-28 | 1972-09-26 | Shell Oil Co | Pipeline for the transport of cold liquids |
| US4130301A (en) * | 1975-01-27 | 1978-12-19 | General Electric Company | Double-walled well casing structure |
| US4340245A (en) * | 1980-07-24 | 1982-07-20 | Conoco Inc. | Insulated prestressed conduit string for heated fluids |
-
1983
- 1983-08-25 JP JP58154259A patent/JPS6018877B2/en not_active Expired
- 1983-08-25 BR BR8304591A patent/BR8304591A/en unknown
- 1983-08-26 CA CA000435504A patent/CA1202578A/en not_active Expired
- 1983-08-29 PH PH29463A patent/PH20499A/en unknown
- 1983-08-29 IN IN1046/CAL/83A patent/IN162701B/en unknown
- 1983-08-30 KR KR1019830004062A patent/KR840005678A/en not_active Application Discontinuation
- 1983-08-31 TR TR21779A patent/TR21779A/en unknown
- 1983-08-31 AT AT83305014T patent/ATE23461T1/en not_active IP Right Cessation
- 1983-08-31 EP EP83305014A patent/EP0104789B1/en not_active Expired
- 1983-08-31 DE DE8383305014T patent/DE3367539D1/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| BR8304591A (en) | 1984-04-03 |
| ATE23461T1 (en) | 1986-11-15 |
| JPS6018877B2 (en) | 1985-05-13 |
| KR840005678A (en) | 1984-11-16 |
| TR21779A (en) | 1985-07-08 |
| EP0104789B1 (en) | 1986-11-12 |
| DE3367539D1 (en) | 1987-01-02 |
| EP0104789A1 (en) | 1984-04-04 |
| JPS5986791A (en) | 1984-05-19 |
| IN162701B (en) | 1988-07-02 |
| PH20499A (en) | 1987-01-21 |
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