CN110516269A

CN110516269A - A kind of optimization for submarine pipeline engineering critical evaluation refers to strain process

Info

Publication number: CN110516269A
Application number: CN201810494745.6A
Authority: CN
Inventors: 徐连勇; 赵晓鑫; 荆洪阳; 韩永典; 赵雷
Original assignee: Tianjin University
Current assignee: Tianjin University
Priority date: 2018-05-22
Filing date: 2018-05-22
Publication date: 2019-11-29
Anticipated expiration: 2038-05-22
Also published as: CN110516269B

Abstract

The present invention discloses a kind of optimization for submarine pipeline engineering critical evaluation with reference to strain process, is based on finite element analysis, introduces the f factor, has searched out fracture response J/ σ₀T and apparent strain ε_nBetween relationship.Pass through a series of derivation in conjunction with Ramberg-Osgood material constitutive relation and with reference to Strain Method failure analysis curvilinear equation, finally obtained the analytical expression with reference to strain, to optimize with reference to Strain Method, realizes more accurate engineering critical assessment.

Description

A kind of optimization for submarine pipeline engineering critical evaluation refers to strain process

Technical field

The invention belongs to field of engineering technology, particularly belong to pipe ring during sea-bottom oil-gas pipeline pipe crimping is laid with and is on active service To the engineering critical assessment technology of face crack, engineering critical assessment is carried out by implementing the technology, it can be determined that pipeline circumferential weld Whether face crack will lead to pipeline failure, to judge whether that safe military service can be continued.

Background technique

With the continuous exploitation of landing field fossil resources, the quantity of land fossil resources is fewer and fewer.Ocean fossil resources obtain The attention of people is arrived.However due to the complexity of deep-marine-environment, deep-sea exploitation has very big technical difficulty.Pipeline is as deep The main carriers of extra large oil gas transport, q&r are most important.Currently used pipe crimping laying method has J-type laying Method, S type laying method and pipe crimping laying method.Wherein pipe crimping laying method efficiency highest may be implemented to weld on the bank and offshore laying.Number Mitron section connects into thousands of meters of pipeline after welding, is then wound on large-scale winding up roller.Laying is transported to by pipe laying barge Place, the processes such as uncoiling, alignment are laid with.During pipe crimping is laid with and is on active service, the name that pipeline will receive 1-4% is answered Change and certain internal pressure.It is lacked due to inevitably generating the harmfulness such as incomplete fusion, lack of penetration, crackle in welding process It falls into.Limitation of these defects due to non-destructive testing technology principle and testing staff's level, partially oriented special tiny flaw meeting Missing inspection.It is therefore desirable to carry out engineering critical assessment to pipeline.Submarine pipeline strain control is directly utilized in conventional reference Strain Method The engineering critical assessment to pipeline may be implemented in the natural boundary conditions of system.However since this method directly uses apparent strain generation For reference strain, thus it may be only available for the lesser Evaluation of Cracks of depth, it is impossible to be used in the assessment of more serious crackle.Because for More serious crackle is very big with reference to the deviation of strain and apparent strain.Directly replace carrying out with reference to strain with apparent strain Assessment is not accurate enough.There is presently no propose containing the analytic formula that accurately reference strains under pipeline internal pressure conditions.

Summary of the invention

It is an object of the invention to overcome the deficiencies of the prior art and provide a kind of for submarine pipeline engineering critical evaluation Optimization refers to strain process, strains formula by the reference derived, improves conventional reference Strain Method, to realize to seabed Accurate engineering critical assessment of the oil-gas pipeline under internal pressure conditions.

Technical purpose of the invention is achieved by following technical proposals:

A kind of optimization for submarine pipeline engineering critical evaluation refers to strain process, carries out as steps described below:

Determine the fracture toughness K of material_mat, solve the stress strength factor K of structure_I, thus according to formula K_r=K_I/K_mat Obtain K_r；According to formulaIt solves and refers to strain stress_ref, then According to reference strain stress_refWith formula D_r=ε_ref/ε₀Determine evaluation point coordinate D_r；

Meanwhile according to formulaWith formula f (D_r)=(2ED_rε₀/σ_ref)^-0.5(D_r> 1) draw failure assessment curve figure (FAC curve, i.e., the critical song for referring to Strain Method Line)；

By evaluation point (D_r,K_r) position be compared with FAC curve, if evaluation point is located above curve, structure is not Safety；If evaluation point is located at below curve, structure safety.

Above-mentioned calculating is applicable in following condition with reference to the formula of strain: it be 0.1-0.4, D/t is 10-that a/t, which is 0.1-0.4, a/c, 30, n be 10-20, n_rFor 0-0.8, ε_n> ε₀。

Above-mentioned calculating is with reference to f in strain formula, by formula J/ σ₀T=f ε_nIt is calculated, to be based on finite element business software Abaqus calculates analysis, introduces the f factor in the solution formula of reference strain, has searched out fracture response J/ σ₀T and name Strain stress_nBetween linear relationship: J/ σ₀T=f ε_n.Wherein J integral can be calculated by business software Abaqus and be solved, apparent strain ε_nFor the strain born in pipeline pipe crimping process of deployment, σ₀For yield strength, unit MPa；T is pipeline wall thickness, unit mm.

Above-mentioned calculating is checked in reference to f in strain formula by table 1- table 3 in embodiment, and 3 data of table 1- table can also be passed through Linear interpolation, which calculates, to be obtained.

It calculates and analyzes the present invention is based on finite element business software Abaqus, introduce f in the solution formula of reference strain The factor has searched out fracture response J/ σ₀T and apparent strain ε_nBetween linear relationship: J/ σ₀T=f ε_n.Wherein J integral is by quotient It is calculated and is solved with software Abaqus.Apparent strain ε_nFor the strain born in pipeline pipe crimping process of deployment.In conjunction with Ramberg- A series of derivation is passed through in Osgood material constitutive relation and reference Strain Method failure analysis curvilinear equation (i.e. formula 1-2), most The analytical expression with reference to strain has been obtained eventually, to optimize with reference to Strain Method, realizes more accurate engineering critical assessment.

Detailed description of the invention

Fig. 1 is the Failure Assessment figure (FAD) that Strain Method is referred to used in the present invention.

Fig. 2 is face crack schematic diagram in the present invention.

Fig. 3 is to assess schematic diagram with reference to Strain Method in the present invention.

Fig. 4 is in the present invention with reference to strain and apparent strain value contrast schematic diagram.

Fig. 5 is the verifying schematic diagram (1) that improvement of the invention refers to Strain Method.

Fig. 6 is the verifying schematic diagram (2) that improvement of the invention refers to Strain Method.

Specific embodiment

Technical solution of the present invention is further illustrated combined with specific embodiments below.

It as shown in Fig. 1, mainly include failure assessment curve (FAC), K with reference to the Failure Assessment figure (FAC) of Strain Method_r And D_r, FAC curvilinear equation, (according to R6 standard), respectively corresponds stretch section and plasticity section, K as shown in formula 1 and formula 2_rAnd D_r's Calculation is respectively as shown in formula 3 and formula 4.

Wherein K_rIt is immeasurable rigid for breaking factor；D_rFor the plastic instability factor, dimensionless；σ_refFor Reference Stress, unit is MPa；σ₀For yield strength, unit MPa.

(2)f(D_r)=(2ED_rε₀/σ_ref)^-0.5(D_r> 1) formula 2

Wherein E is elasticity modulus, unit MPa, ε₀For yield strain, dimensionless.

(3)K_r=K_I/K_matFormula 3

Wherein K_IFor stress intensity factor, unit isK_matFor material fracture toughness, unit is

(4)D_r=ε_ref/ε₀Formula 4

Wherein ε_refFor with reference to strain, dimensionless.

(i.e. conventional reference Strain Method) is by ε in the prior art_refDirectly use apparent strain ε_nInstead of being incited somebody to action that is, in formula 4 ε_refDirectly use apparent strain ε_nIt is not accurate enough for the assessment result obtained compared with deep torn grain instead of carrying out the calculating of Dr.The present invention It is middle to propose to carry out using formula 5 that obtained reference is strained substitution formula 4 and is calculated, such as formula 5 is used with reference to strain calculation Shown in reference to strain formula carry out assessing available more accurate assessment result.

Wherein α is material parameter, α=1；σ₀For yield strength, unit MPa；ε₀For yield strain, dimensionless；ε_nIt runs after fame Justice strain, dimensionless；T is pipeline wall thickness, unit mm；F is a parameter introducing in formulation process, dimensionless, Value is as shown in table 1-3；N is strain hardening exponent, dimensionless；J integral representation crack driving force for propagation, J_eFor the elasticity of J integral Component can be acquired by formula 8, can also be by (J integral is calculated by business software Abaqus to be solved), J is calculated_eWith J unit It is Mpamm.

1 f value of table is based on n=10, a/t=0.1-0.4, a/c=0.1-0.4, D/t=10-30, n_r=0-0.8

Such as f=0.649, corresponding n=10, a/t=0.1, a/c=0.1, D/t=10, n_r=0；F=0.435, corresponding n =10, a/t=0.1, a/c=0.4, D/t=30, n_r=0.2.

2 f value of table is based on n=15, a/t=0.1-0.4, a/c=0.1-0.4, D/t=10-30and n_r=0-0.8

Such as f=11.497, corresponding n=15, a/t=0.4, a/c=0.1, D/t=10, n_r=0；F=0.704, it is corresponding N=15, a/t=0.1, a/c=0.4, D/t=10, n_r=0.4.

3 f value of table is based on n=20, a/t=0.1-0.4, a/c=0.1-0.4, D/t=10-30and n_r=0-0.8

Such as f=1.727, corresponding n=20, a/t=0.2, a/c=0.1, D/t=10, n_r=0；F=4.599, corresponding n =20, a/t=0.4, a/c=0.4, D/t=20, n_r=0.2.

Wherein a is pipe surface crack depth, unit mm；C is half length of face crack, unit mm；D is outside pipeline Diameter, unit mm；T is pipeline wall thickness, unit mm；n_rFor the amount for characterizing pipeline internal pressure, dimensionless is determined by formula 6-7.

n_r=σ_h/σ₀Formula 6

Wherein σ_hFor the circumferential stress that pipeline is born, unit MPa, σ₀For yield strength, unit MPa is true by formula 7 It is fixed

σ_h=P (D-2t)/2t formula 7

Wherein P is that pipeline bears internal pressure size, unit MPa.

Wherein ν is Poisson's ratio, dimensionless, K_IFor stress intensity factor, unit isE is elasticity modulus, MPa。

It is calculated and is analyzed based on finite element business software Abaqus, introduced the f factor in the solution formula of reference strain, seek Have found fracture response J/ σ₀T and apparent strain ε_nBetween linear relationship: J/ σ₀T=f ε_n.Wherein J integral can be by commercial soft Part Abaqus, which is calculated, to be solved, apparent strain ε_nFor the strain born in pipeline pipe crimping process of deployment, in conjunction with Ramberg- Osgood material constitutive relation and reference Strain Method failure analysis curvilinear equation (i.e. formula 1-2), have finally obtained with reference to strain Analytical expression realize more accurate engineering critical assessment to optimize with reference to Strain Method.

When being evaluated, the fracture toughness K of material is determined_mat, solve the stress strength factor K of structure_I, thus according to Formula K_r=/K_IObtain K_r；According to formulaSolve ginseng Examine strain stress_ref, further according to reference strain stress_refWith formula D_r=ε_ref/ε₀Determine evaluation point coordinate D_r；

By evaluation point (D_r,K_r) position be compared with FAC curve, if evaluation point is located above curve, structure is not Safety；If evaluation point is located at below curve, structure safety, as shown in Fig. 3.

As shown in Fig. 4, for different pipeline configuration and crack size, the reference of proposition is strained into formula and name is answered Variate compares, with reference to only special case situation equal with apparent strain is strained, for higher a/t and lower D/t value (being equivalent to severe crack) is greater than apparent strain with reference to strain, and conventional reference Strain Method can obtain non-conservative assessment at this time；It is right In lower a/t and higher D/t (being equivalent to crackle), it is less than apparent strain with reference to strain, at this time conventional reference Strain Method It can obtain overly conservative assessment.

As depicted in figures 5 and 6, the embodiment verifying that the formula 5 proposed according to the present invention obtains, assumes fracture in figure Toughness J_ICIt is equal with crack driving force for propagation J, therefore obtained evaluation point result should be fallen on curve.Conventional method is in pipe Road Crack Parameters a/t=0.1, a/c=0.1, D/t=30, ε_nWhen=0-4% (Fig. 5), evaluation point is substantially all in FAC curve Top, and work as a/t=0.4, a/c=0.1, D/t=10, ε_nWhen=0-4% (Fig. 6), obtained evaluation point all exists substantially The lower section of FAC curve.In comparison, the evaluation point obtained according to the formula of proposition 5 all on curve, can prove this substantially Formula substantially increases the accuracy of engineering critical assessment.

Physics scale used herein, as follows:

Illustrative description has been done to the present invention above, it should explanation, the case where not departing from core of the invention Under, any simple deformation, modification or other skilled in the art can not spend the equivalent replacement of creative work equal Fall into protection scope of the present invention.

Claims

1. a kind of optimization for submarine pipeline engineering critical evaluation refers to strain process, which is characterized in that as steps described below It carries out:

Determine the fracture toughness K of material_mat, solve the stress strength factor K of structure_I, thus according to formula K_r=K_I/K_matIt obtains K_r；According to formulaIt solves and refers to strain stress_ref, then root According to reference strain stress_refWith formula D_r=ε_ref/ε₀Determine evaluation point coordinate D_r；

Meanwhile according to formulaWith formula f (D_r)= (2ED_rε₀/σ_ref)^-0.5(D_r> 1) draw the failure assessment curve figure (FAC curve, i.e. critical curve) for referring to Strain Method；

By evaluation point (D_r,K_r) position be compared with FAC curve, if evaluation point is located above curve, structure is uneasy Entirely；If evaluation point is located at below curve, structure safety；Wherein K_rIt is immeasurable rigid for breaking factor；D_rFor the plastic instability factor, Dimensionless；σ_refFor Reference Stress, unit MPa；σ₀For yield strength, unit MPa；E is elasticity modulus, unit MPa, ε₀ For yield strain, dimensionless；K_IFor stress intensity factor, unit isK_matFor material fracture toughness, unit isε_refFor with reference to strain, dimensionless；α is material parameter, α=1；σ₀For yield strength, unit MPa；ε₀It is in the wrong Clothes strain, dimensionless；ε_nFor apparent strain, dimensionless；T is pipeline wall thickness, unit mm；N is strain hardening exponent, immeasurable Guiding principle；J integral representation crack driving force for propagation, J_eFor the component of elasticity of J integral, J_eIt is Mpamm with J unit；F is by formula J/ σ₀T=f ε_nIt is calculated, dimensionless, is obtained with calculating analysis based on finite element business software Abaqus.

2. a kind of optimization for submarine pipeline engineering critical evaluation according to claim 1 refers to strain process, special Sign is, calculates the formula with reference to strain and is applicable in following condition: it be 0.1-0.4, D/t is 10-30, n that a/t, which is 0.1-0.4, a/c, For 10-20, n_rFor 0-0.8, ε_n> ε₀, a is face crack depth, unit mm；T is pipeline wall thickness, unit mm；C is that crackle half is long Degree, unit mm；D is outer diameter tube, unit mm；N is strain hardening exponent, dimensionless；n_rFor circumferential stress ratio, dimensionless；ε_nFor Apparent strain, dimensionless；ε₀For yield strain, dimensionless.

3. a kind of optimization for submarine pipeline engineering critical evaluation according to claim 1 refers to strain process, special Sign is that f is checked in by following table 1-table 3, is obtained by the linear interpolation calculation of 3 data of table 1- table.