CN113486546A - Design method for realizing self-limiting of small-caliber steel catenary riser - Google Patents
Design method for realizing self-limiting of small-caliber steel catenary riser Download PDFInfo
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- CN113486546A CN113486546A CN202110621219.3A CN202110621219A CN113486546A CN 113486546 A CN113486546 A CN 113486546A CN 202110621219 A CN202110621219 A CN 202110621219A CN 113486546 A CN113486546 A CN 113486546A
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Abstract
The invention provides a design method capable of realizing self-limiting of a small-caliber steel catenary riser, which comprises the following steps of: calculating the length from the small-caliber steel catenary riser to the underwater terminal facility; establishing a digital seabed; calculating the contact parameters of the seabed and the riser; establishing a steel catenary riser analysis model; horizontally placing the steel catenary riser on a digital seabed, establishing a contact relation between a pipe body and a terminal facility and the seabed, and simulating a laying state; suspending the steel catenary riser at a virtual suspension point by using quasi-static finite element analysis, and simulating the in-place initial condition of the riser; under the design sea condition, initially translating the position of the suspension point; carrying out dynamic time domain analysis on the whole vertical pipe, and extracting a vertical pipe terminal displacement time course result; judging whether the riser terminal meets the displacement bearing requirement of the jumper pipe; design improvement; the self-limiting design of the steel catenary riser is completed, the technical requirement of the self-limiting design is met, and self-limiting under the condition that an underwater limiting structure is not required to be added on the pipe body.
Description
Technical Field
The invention belongs to the design technology of deepwater ocean engineering, and particularly relates to a design method capable of realizing self-limiting of a small-diameter steel catenary riser.
Background
A steel catenary riser belongs to the field of deepwater ocean engineering (the water depth is more than 1000 meters), and is mainly used for conveying production media between an underwater production facility and a floating platform. The SCR, driven by the motion of the floating platform, generates a certain tension load on the deepwater marine pipe connected to it and its end facilities (PLET, connectors, jumpers, etc.). If the load is too large, the end facilities are driven to move, the integrity of the connector and the jumper pipe is affected and even damaged, and the problems of leakage and the like are caused. The existing engineering processing method mainly comprises the steps of obtaining the maximum tension of the bottom of a vertical pipe through the motion analysis of the steel catenary vertical pipe in an in-place extreme condition, judging whether an end facility can displace or not through the comparison of tension load and resistance of the underwater facility, and generally adding an underwater structure on a mud-laying section of the steel catenary vertical pipe to limit the displacement of the end facility in engineering for the end facility which is likely to move. The method for processing the small-diameter steel catenary riser often causes over-conservative results, and has two main reasons: firstly, the whole process is a mechanical working condition of displacement control, and the actual condition cannot be reflected only by comparing tension load with resistance; and secondly, finite element analysis of the steel catenary riser, which is developed in the current engineering, is directly constructed in an in-place catenary shape, and subsequent analysis is developed on the basis of the in-place catenary riser finite element analysis. Due to the reasons, the conventional design method is adopted, so that extra underwater structures are added to the small-diameter steel catenary riser, and the investment cost of deepwater engineering is greatly increased.
Disclosure of Invention
The invention provides a design method for a small-diameter steel catenary riser (6 inches or less), which avoids the conservative result of the conventional design method and realizes self-limiting of the small-diameter steel catenary riser without adding an underwater limiting structure to a pipe body.
In order to realize the purpose of the invention, the following technical scheme is adopted:
s1, calculating the length from the small-caliber steel catenary riser to the underwater terminal facility by using a catenary theory based on the arrangement of the underwater terminal facility and the floating platform, wherein the calculation formula is as follows;
wherein z is the water depth of the bottom contact point of the steel catenary riser, s is the length of the steel catenary riser, x is the projection length from the suspension point to the bottom contact point, and theta is the suspension angle;
s2, constructing a three-dimensional digital seabed from the suspension position of the steel catenary riser to the underwater terminal according to the water depth investigation data;
s3, calculating the contact input parameters of the three-dimensional seabed and the riser according to the soil geological parameters, which mainly comprises the following steps:
a. the elastic stiffness of the three-dimensional seabed is calculated according to the corresponding relation between the settlement of the soil in the pipeline and the self weight of the pipe body, and the formula is as follows:
wherein z is the settling volume of the riser, QVIs the contact force between the pipe body and soil, D is the outer diameter of the vertical pipe, gamma' is the underwater unit weight of the soil, SuThe soil shear strength;
b. the axial friction coefficient of the three-dimensional seabed is calculated according to the following formula:
in the formula ofAIs the axial coefficient of friction, epsilonresIs resistance reduction coefficient, alpha is pipe soil roughness coefficient, (S)u/σ′v)NCThe ratio of the soil shear strength to the vertical effective stress,
for over compression ratio, γrateIs the load ratio.
And S4, establishing a finite element model according to the length of the whole steel catenary riser calculated in the S1 by using the three-node pipe units, wherein the terminal facility part of the steel catenary riser is simulated by using equivalent pipe units according to the underwater weight and the main size of the terminal facility part of the steel catenary riser and is used for calculating the terminal moving distance in the later period.
S5, horizontally arranging the steel catenary riser on a three-dimensional seabed, establishing a contact relation between the pipe body and a terminal facility and the three-dimensional seabed, applying laying residual tension on the end part, simulating a laying state, and partially starting the interaction of the riser and the seabed;
s6, calculating the shape of the catenary according to the step S1, suspending the steel catenary riser at a virtual suspension point by using quasi-static finite element analysis, simulating the initial situation of the riser in place, and further starting the interaction of the riser and the seabed under the action of the initial tension of the riser;
s7, according to the extreme marine environment needing to be calculated, translating the position of the suspension point according to the initial moving distance of the floating platform under the far-end working condition, and fully starting the interaction between the mud landing part of the steel catenary riser and the seabed;
s8, carrying out dynamic time domain analysis on the whole steel catenary riser according to the motion time course data of the floating platform under extreme sea conditions, and extracting the displacement time course result of the steel catenary riser terminal facility model;
and S9, judging whether the displacement result of the steel catenary riser terminal meets the design requirement, wherein the judgment standard is that the displacement of the steel catenary riser terminal is smaller than the allowable displacement load of the jumper. If the design requirement is satisfied, executing step S11, and if the design requirement is not satisfied, executing step S10;
s10: reducing the displacement of the steel catenary riser terminal based on the tension generated at the steel catenary riser terminal in the analysis, and evaluating whether the steel catenary riser system can realize self-limiting or not according to the flow of the steps S3-S9;
and S11, finishing the self-limiting design of the steel catenary riser and providing that the terminal and the pipe body of the steel catenary riser meet the technical requirements of the self-limiting design.
Further, in step S9: and (4) using the displacement result evaluation standard of the steel catenary riser terminal.
Further, the method also comprises the steps of laying and installing the steel catenary riser, performing a hydraulic test, normally operating the steel catenary riser and performing the whole service period of extreme working conditions possibly encountered in the service life, and simultaneously considering the influence of friction starting and remodeling of the seabed soil.
Further, the weight and termination of the steel catenary riser system is designed to meet the self-limiting design of the steel catenary riser system based on small pipe diameter.
Further, in step S10: the method for reducing the displacement of the steel catenary riser terminal is one or a combination of more of increasing the weight of the steel catenary riser terminal facility, increasing the height of a skirt plate of the terminal facility or increasing the weight of the steel catenary riser body system.
The invention has the beneficial effects that: judging a standard based on a displacement control result; considering the influence of friction starting and remolding of the seabed soil when the steel catenary riser is laid, installed, subjected to hydrostatic test, normally operated and possibly subjected to extreme working conditions in the service life in the whole service period; the design requirement of self-limiting is met for the small-caliber steel catenary riser system, and self-limiting of the small-caliber steel catenary riser is achieved without adding an underwater limiting structure to the pipe body. The engineering investment cost is greatly reduced while the purposes of protecting the integrity and safety of the end part facilities of the deepwater sea pipe and the underwater facilities connected with the end part facilities are achieved.
Drawings
FIG. 1 is a schematic flow chart of a design method for achieving self-limiting of a small-caliber steel catenary riser according to the present invention;
FIG. 2 is a schematic layout of a steel catenary riser and vessel arrangement for implementing a design method for self-limiting of a small pipe diameter steel catenary riser according to the present invention;
FIG. 3 is a schematic structural diagram of a digital seabed according to the design method for realizing self-limiting of a small-caliber steel catenary riser of the invention;
fig. 4 is a schematic diagram of the relationship between the displacement distance of the riser terminal and the time according to the design method for realizing the self-limiting of the small-caliber steel catenary riser.
Detailed Description
The present invention is further described with reference to the following drawings and specific examples so that those skilled in the art can better understand the present invention and can practice the present invention, but the examples are not intended to limit the present invention.
The technical scheme of the invention is explained in more detail by taking a 6-inch steel catenary riser as a case:
s1: according to the SCR shown in fig. 2, the water depth 1434 m, the suspension angle 10 degrees, according to the catenary theoretical formula,
calculating to obtain the length from the suspension point to the riser terminal and the projection length from the suspension point to the TDP;
s2: surveying the water depth along the direction of the steel catenary riser to establish a digital seabed as shown in figure 3;
s3: calculating settlement formula according to data of a plurality of soil drilling points along the route
And calculating the formula of the axial friction force of the pipe and soil
The settlement of the vertical pipe is 32.2mm, the equivalent seabed rigidity is 20313N/m/m, and the pipe-soil axial friction coefficient is 0.2;
s4: using ABAQUS or FLEXCOM as a finite element analysis tool, using a three-node pipe unit, calculating the length of the riser according to the step 1 to establish a model, wherein the outer diameter of the riser unit is 168.3mm, the wall thickness is 18.3mm, the weight of a terminal facility is 90MT, and using a pipe unit with the length of 4 meters and the outer diameter of 1 meter to perform equivalent simulation according to the principle that the underwater weight is kept consistent.
S5: establishing a contact elastic body seabed model according to the digital seabed, and inputting the friction coefficient and the rigidity calculated in the step 3;
s6: flatly placing the integral model of the stand pipe on a seabed model, establishing a contact relation, applying laying residual tension on the end part, and simulating a laying state, wherein the laying tension is 17 MT;
s7: calculating the shape of a catenary according to the step 1, respectively loading and displacing 1400m and 720m of the end part of a steel catenary riser along the water depth direction and horizontal direction in finite element analysis, and simulating the suspension of the riser at a designed suspension point and the initial in-place condition of the riser;
s8: taking the 1000-year-first sea condition as an extreme marine environment for accounting, wherein the initial moving distance of the floating platform under the far-end working condition is 70 meters, applying the displacement load on the end part of the riser model, and fully starting the interaction between the mud laying part of the steel catenary riser and the seabed;
s9: according to the motion time-course data of the floating platform under the condition of meeting sea for 1000 years, performing dynamic time-domain analysis on the whole steel catenary riser for at least 3 hours to obtain a displacement time-course result of the steel catenary riser terminal facility model, wherein the accumulated displacement is 0.945 meter as shown in fig. 4;
s10: judging whether the displacement of the riser terminal meets the displacement load requirement of the end part of the terminal jumper pipe, if so, enabling the riser system to meet the self-limiting requirement, and if not, needing to increase the weight of the riser system or the height of a terminal apron board, and redesigning according to the steps 3-9;
s11: in the case, the unit weight of the pipe body is increased by 8%, the counterweight 10MT is added at the vertical pipe terminal, and the displacement of the vertical pipe terminal is redesigned and calculated, so that the result is 0.75 m, and the design load of most of the jumper pipes can be met;
s12: the self-limiting design of the small-diameter steel catenary riser is completed, the wall thickness of the riser is required to be within a manufacturing tolerance range of-5% -20% to that of the riser (the manufacturing tolerance requirement can meet the unit weight of the riser to be + 8%), and the design weight of the riser terminal is required to be 100MT at minimum.
The above-mentioned embodiments are merely preferred embodiments for fully illustrating the present invention, and the scope of the present invention is not limited thereto. The equivalent substitution or change made by the technical personnel in the technical field on the basis of the invention is all within the protection scope of the invention. The protection scope of the invention is subject to the claims.
Claims (5)
1. A design method for realizing self-limiting of a small-caliber steel catenary riser is characterized by comprising the following steps: the method comprises the following steps:
s1, calculating the length from the small-caliber steel catenary riser to the underwater terminal facility by using a catenary theory based on the underwater terminal facility and the floating platform arrangement, wherein the calculation formula is as follows:
wherein z is the water depth of the bottom contact point of the steel catenary riser, s is the length of the steel catenary riser, x is the projection length from the suspension point to the bottom contact point, and theta is the suspension angle;
s2, constructing a digital seabed from the suspension position of the steel catenary riser to an underwater terminal according to the water depth investigation data;
s3, calculating the contact input parameters of the seabed and the riser according to the soil geological sampling parameters, wherein the calculation steps comprise:
s31: the digital seabed elastic stiffness is calculated through the corresponding relation between the settlement of the soil in the pipeline and the self weight of the pipe body, and the formula is as follows:
wherein z is the settling volume of the riser, QVIs the contact force between the pipe body and the soil, D is the outer diameter of the vertical pipe, gamma' is the underwater unit weight of the soil, SuThe soil shear strength;
s32: the digital seabed axial friction coefficient is calculated according to the following formula:
in the formula ofAIs the axial coefficient of friction, epsilonresIs resistance reduction coefficient, alpha is pipe soil roughness coefficient, (S)u/σv′)NCThe ratio of the soil shear strength to the vertical effective stress,
for over compression ratio, γrateIs the load ratio.
S4, establishing a finite element model according to the length of the whole steel catenary riser calculated in the step S1 by using a three-node pipe unit, wherein a steel catenary riser terminal facility part is simulated by using an equivalent pipe unit according to the underwater weight and the main size of the steel catenary riser terminal facility part and is used for calculating the terminal moving distance in the later stage;
s5, horizontally arranging the steel catenary riser on the digital seabed, establishing the contact relation between the pipe body and the terminal facilities and the digital seabed, applying laying residual tension on the end part, simulating the laying state after simulation, and partially starting the interaction of the riser and the seabed;
s6, calculating the shape of the catenary according to the step S1, suspending the steel catenary riser at a virtual suspension point by using quasi-static finite element analysis, simulating the initial situation of the riser in place, and further starting the interaction of the riser and the seabed under the action of the initial tension of the riser;
s7, according to the extreme marine environment needing to be calculated, translating the position of the suspension point according to the initial moving distance of the floating platform under the far-end working condition, and fully starting the interaction between the mud landing part of the steel catenary riser and the seabed;
s8, carrying out dynamic time domain analysis on the whole steel catenary riser according to the motion time course data of the floating platform under extreme sea conditions, and extracting the displacement time course result of the steel catenary riser terminal facility model;
s9, judging whether the displacement result of the steel catenary riser terminal meets the design requirement, wherein the judgment standard is that the displacement of the steel catenary riser terminal is smaller than the allowable displacement load of the jumper pipe, if the displacement result meets the design requirement, executing the step S11, and if the displacement result does not meet the design requirement, executing the step S10;
s10: reducing the displacement of the steel catenary riser terminal based on the tension generated at the steel catenary riser terminal in the analysis, and evaluating whether the steel catenary riser system can realize self-limiting or not according to the flow of the steps S3-S9;
and S11, finishing the self-limiting design of the steel catenary riser and providing that the terminal and the pipe body of the steel catenary riser meet the technical requirements of the self-limiting design.
2. The small-caliber steel catenary riser self-limiting design method of claim 1, wherein in step S9: and (4) using the displacement result evaluation standard of the steel catenary riser terminal.
3. The method of claim 1, further comprising the step of considering the effects of friction initiation and remodeling of seabed soil on the entire service cycle of the steel catenary riser during installation, hydrostatic testing, normal operation, and extreme conditions that may be encountered during life.
4. The method of small pipe diameter steel catenary riser self-limiting design of claim 1, wherein the weight and termination of the steel catenary riser system are designed to meet the design of small pipe diameter steel catenary riser system self-limiting.
5. The small-caliber steel catenary riser self-limiting design method of claim 1, wherein in step S10: the method for reducing the displacement of the steel catenary riser terminal is one or a combination of more of increasing the weight of the steel catenary riser terminal facility, increasing the height of a skirt plate of the terminal facility or increasing the weight of the steel catenary riser body system.
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