Clad Pipe Research Articles

Local and global mechanical properties of orbital friction stir welding on API X65 PSL2 steel / Inconel 625 clad pipes

Orbital friction stir welding (FSW) is a promising approach to joining clad pipes. In this work, the influence of individual process parameters on the material flow even as, mechanical properties in orbital friction stir welded clad pipes is investigated. Due to the local heterogeneous microstructures within the weld, joints were evaluated by optical and scanning electron microscopy (SEM), microhardness, and digital image correlation (DIC). A microhardness increase was observed, with a maximum of 380 HV0.5 within the Inconel 625 and 265 HV0.5 within the X65 steel stir zones. Sound joints had an average ultimate tensile strength (UTS) exceeding up to 13% of the calculated theoretical tensile strength, which is obtained considering the minimum tensile strength of both materials. Additionally, failure occurred in the base material during the tensile testing, where the local strain in the stir zones of the X65 steel and Inconel 625 were only 3.3% and 10%, respectively. In summary, this investigation shows friction stir welded joints of API X65 steel and Inconel 625 clad pipes with high mechanical properties.

Hydrogen-induced failure analysis of bimetallic clad pipes

This study investigated the mechanical properties and fracture characteristics of an alloy 825/L360 bimetallic clad pipe after it was subjected to hydrogen charging. The results indicated that the elongation loss of the pipe increased from 12.3% to 50.0% with increasing hydrogen charging time. In addition, results obtained from hydrogen microprinting and scanning Kelvin probe force microscopy indicated that the hydrogen distribution characteristics of the aforementioned material influenced the hydrogen fracture failure mechanism of the clad pipe. Specifically, carbides and TiN initiated hydrogen cracking, and crack extension occurred through brittle cracking at grain boundaries, which was caused by the interaction of hydrogen with dislocation slip bands within the dendritic zone.

Feasibility of orbital friction stir welding on clad pipes of API X65 steel and Inconel 625

Orbital friction stir welding (FSW) has been applied to clad pipes, which is certainly of interest to the oil and gas industry. In this context, an FSW system capable of performing sound joints in one pass with full tool penetration was developed. Orbital FSW was executed in 6 mm thick API X65 PSL2 steel clad pipes with 3 mm thick Inconel 625 using a polycrystalline cubic boron nitride (pcBN) tool. The metallurgical and mechanical properties of the joints were investigated. Sound joints with axial forces of 45–50 kN, tool rotational speeds of 400–500 rpm, and a welding speed of 2 mm/s were obtained, illustrating that the developed system can perform FSW joints without volumetric defects.

Study of joint hot deformation of nickel alloy and low carbon microalloyed steel in manufacture of heavy plate clad rolled products

Clad pipes are widely used worldwide for transportation of oil and gas under conditions of exposure to aggressive media. The article investigates the issue of joint deformation of nickel alloy and steel of strength class K60 during production of rolled heavy plates on the industrial plate mill. The rheological properties of the constituent materials were determined, the mathematical model based on the finite element method was developed; it allowed to determine the dependence of deformation ratio of the layers on the total deformation of the billet. Accuracy of the results obtained using simulation is confirmed by comparison with the results of industrial rolling. The obtained relationships allow proper selection of the initial thickness of the stainless layer billet, which provides the required final thickness of the clad layer. The studies were carried out within the program of the Russian Federation of strategic academic leadership "Priority-2030" aimed at supporting the development programs of educational institutions of higher education, the scientific project PRIOR/SN/NU/22/SP5/26.

A numerical study on the correlation of ductile crack extension in Ni-based clad pipe girth welds with circumferential surface cracks and clamped SE(T) specimens

This work describes a numerical investigation on the relationships between ductile crack extension in Ni-based clad pipe girth welds and an API X80 pipeline steel with circumferential surface cracks and SE(T) specimens under fixed grip conditions. A primary objective is to gain further insight and understanding of the effects of constraint on ductile tearing behavior in piping components with dissimilar girth welds and how well crack growth resistance curves measured using single edge notched tension fracture specimens correlate with ductile fracture behavior in circumferentially surface cracked pipes. The numerical description of CTOD−R curves employs a computational cell approach incorporating the Gurson–Tvergaard (GT) constitutive model to simulate ductile crack extension in the crack configurations analyzed. The numerical analyses consider predictions of ductile crack growth in 3-D models of circumferentially cracked pipes with varying crack depth over pipe thickness ratio, a/t, from measured J-resistance curves derived from fracture resistance testing of clamped SE(T) specimens. The analyses also focus on comparing predictions of ductile crack extension using two different definitions for the CTOD.

Buckling failure mechanism of liner pipe in bimetal mechanical clad pipe under complex loading

Bimetal mechanical clad pipe is one of the main measures for anti-corrosion control adopted in oil and gas fields. The liner pipe failure is a key problem that restricting the clad pipe applications. In this paper, a calculation model of clad pipe is established, and the buckling failure of liner pipe under complex loading was investigated. Effects of forming process, working pressure, external environmental loading and structural parameters on the failure mode of liner pipe were studied. The results show that increasing the residual contact pressure in the forming process is helpful to improve the buckling resistance of the liner pipe. The residual stress between liner and outer pipes can make the clad pipes bear a larger bending loads and have a larger critical curvature. Buckling mode “8” of the liner pipe occurs under complex loading. A larger working pressure can reduce the buckling degree and fold amplitude of the liner pipe. The liner pipe is more resistant to buckling in shallow water than in deep water. With the increasing of the wall thickness for liner and outer pipes, buckling resistance of the liner pipe becomes stronger. Finally, prediction formulas for critical curvature and the maximum normalized bending moment of the clad pipe are presented. The research results can provide a theoretical basis for the design, manufacture, and safety evaluation of clad pipe.

Results of validation and cross-verification of the ROK/B design code on the problem of loss of cooling in the spent fuel pool *

The procedures of validation and cross-verification of the newly developed computational code ROK/B are described. The main problem solved using the ROK/B code is the substantiation by calculation of the coolant density in the spent fuel pool (SFP) and the temperature regime of the fuel assemblies during a protracted shutdown of the cooling systems (break in the supply of cooling water). In addition to the above, it is possible to use the ROK/B code to carry out calculation of an accident with the discharge of the coolant from the SFP with simultaneous prolonged shutdown of the cooling systems. The ROK/B code allows carrying out calculations for various types of designs of the fuel assemblies and VVER reactors, in particular, VVER-1000, VVER-1200 and VVER-440 power units with single- and two-tiered fuel assembly arrangement, with clad pipes in racks (for compacted assemblies storage) and pipes without cladding, with cased assemblies and caseless ones. During fuel reloading, a high level of the coolant is maintained, which makes it possible to do “wet” transportation of the assemblies from the reactor to the SFP. The mathematical model for heat and mass transfer calculation, including the boiling coolant model, implemented in the ROK/B code, includes: the motion equation, equations for calculating the enthalpy along the height of the fuel section of a fuel assembly with natural circulation of coolant within the channel containing the fuel assembly (lifting section) and in the inter-channel space (lowering section), the equation of mass balance between the channels of the racks with assemblies and in the inter-assembly space and the amount of evaporated (and outflowed) water, the heat balance equation for a fuel rod in a steam environment. The system of equations is supplemented by closing relations for calculating the thermal physics properties of water and steam, fuel and cladding materials, as well as the coefficients of heat transfer from the wall to the steam, hydraulic resistance and density of the steam-water mixture in the channels, and the heat released in the reaction of steam with zirconium. Validation of the computational code was carried out on the basis of the data of the ALADIN experiment performed by German specialists and the data of JSC OKB Gidropress. Cross-verification of the ROK/B code was carried out in comparison with the results of calculation using the KORSAR/GP and SOKRAT/B1 codes. Based on the results of the validation, it has been concluded that the deviation of the ROK/B results from the experimental data is not more than 2 to 10% (10% for the option with a fuel rod power of 20 W). Based on the results of cross-verification, it has been concluded that the discrepancy between the ROK/B results and the calculation results for the KORSAR/GP and SOKRAT/B1 codes is not more than 0.5% (for SOKRAT/V1) and less than 10% (for KORSAR/GP).

Theoretical Study on Thermal Hydraulic Expansion Process of Stainless Steel Lined Clad Pipe

Abstract The stainless steel lined clad pipe (SSLCP) can be widely used in different fields. Industrial SSLCP are generally manufactured by the cold hydraulic expansion (CHE) method which requires high hydraulic pressure and good sealing property. The interlayer bonding force is difficult to obtain by the CHE when there is little difference between the yield strengths of inner and outer pipes. Furthermore, the hydraulic expansion process nearly cannot be achieved when the yield strength of inner pipe is higher than that of outer pipe. The thermal hydraulic expansion (THE) method can overcome these difficulties. In this paper, the graph method was adopted to analyze the THE principles for “inner strong and outer weak (ISOW)” and “outer strong and inner weak (OSIW)” pipes. The effective hydraulic expansion criterion conditions of SSLCPs were proposed and can be used as basis of clad pipe material matching and forming process selection. Through the stress and strain analysis of inner and outer pipes during THE process, the deformation coordination conditions of elastic deformation and thermal deformation of the inner and outer pipe were established. The correlation between the residual contact pressure p*c, the hydraulic expansion pressure pi, and the effective temperature difference ΔTe were derived. The calculation formula of the maximum expansion pressure pimax and the minimum expansion pressure pimin was obtained. The maximum heating temperature of outer pipe was also derived. Furthermore, the finite element analysis (FEA) method was adopted and simulated results verify the feasibility and applicability of the theory study.

J estimation based on regression machine learning applied to circumferential surface clad pipes with V groove weld

A regression machine learning approach is applied to propose a new equation for J-integral estimation for circumferential surface clad pipelines. The training data is provided based on a large number of simulations accomplished using a parametric finite element model generator script. The analysis matrix includes several crack depth ratios a/t, crack aspect ratios c/a, pipe diameter ratios Dext/t, V-groove angle, and material strain hardening exponent, n. The clad layer thickness is considered fixed with 3 mm. A model generator based on the Python programming language is used to generate an extensive data set of models. Training and testing sets are formed for five features and one target to develop a machine learning model. This paper aims mainly to promote fracture assessments by presenting an easy-to-use regression model encompassing several geometrical and material parameters. This is for finding an initial conservative J-integral estimation for a fully plastic description of fracture behavior under considerable plastic strain to provide a numerical evaluation of the crack driving force. The validation of the proposed model is ensured by comparing the results herein with those from different approaches.

Analysis of Welding Technology about Bimetallic Clad Pipelines

Butt girth welding was a knotty problem for future application of bimetallic clad pipelines. At present, there were two kinds of problems: 1) To decide whether to use a variety of alloy welding procedure or to use corrosion resistant alloy full welding procedure; 2) After selecting the procedure, what kind of welding material should be equipped. In view of the above problems, taking 316L SS or 2205 DSS clad pipe as an example, welding process design and experimental analysis were conduted in this paper. Analysis of welding process from theory, standard and practice pointed out the control of welding hardness under different welding materials and procedure and directional suggestions of welding for bimetallic clad pipelines were provided. Futher the hardness distribution and CVN absorbed Energy test results of different welding processes showed welding quality could be guaranteed only when ENiCrMo-3 welding material was chosen for the whole weld.

J-resistance curve testing of a pressure vessel steel and a clad pipe girth weld using clamped SE(T) specimens and the normalization method

This work addresses an exploratory application of the normalization method to determine crack growth resistance curves for a typical pressure vessel steel and a clad pipe girth weld using clamped SE(T) specimens. A primary objective is to verify the effectiveness of the methodology in providing accurate descriptions of the ductile properties for the tested materials using clamped SE(T) specimens. Fracture toughness testing conducted on an A285 Gr C pressure vessel steel and a dissimilar Nickel–Chromium girth weld provides the load–displacement data from which J-resistance curves are evaluated on the basis of the normalization procedure. For the tested pressure vessel steel and clad pipe girth weld, the normalization method provides experimental measurements of ductile crack extension in terms of J−Δa curves which are in good agreement with experimentally measured crack growth responses derived from the UC procedure.

Occurrence and quantification of culturable and viable but non-culturable (VBNC) pathogens in biofilm on different pipes from a metropolitan drinking water distribution system

Waterborne pathogens have been found in biofilms grown in drinking water distribution system (DWDS). However, there is a lack of quantitative study on the culturability of pathogens in biofilms from metropolitan DWDS. In this study, we quantified culturable and viable but non-culturable (VBNC) Escherichia coli, Salmonella enterica, Pseudomonas aeruginosa and Vibrio cholerae in biofilms collected from five kinds of pipes (galvanized steel pipe, steel pipe, stainless steel clad pipe, ductile cast iron pipe and polyethylene pipe) and associated drinking water at an actual chlorinated DWDS in use from China. The results of these comprehensive analyses revealed that pipe material is a significant factor influencing the culturability of pathogen and microbial communities. Network analysis of the culturable pathogens and 16S rRNA gene inferred potential interactions between microbiome and culturability of pathogens. Although the water quality met the Chinese national standard of drinking water, however, VBNC pathogens were detected in both biofilms and water from the DWDS. This investigation suggests that stainless steel clad pipe (SSCP) was a better choice for pathogen control compared with other metal pipes. To our knowledge, this is the first study on culturable and VBNC pathogens in biofilms of different pipe materials in metropolitan DWDS.

Double-Sided Welding as an Alternative for Joining Internally Clad Pipes

AbstractHigh strength steel pipes internally clad with nickel (Ni) superalloys are components widely used in the oil and gas industry in the production of rigid risers. The joining of clad pipes is...

Strain-based fracture assessment for an interface crack in clad pipes under complicated loading conditions

In welded clad pipelines, the weld toe is a critical failure position due to the combined effects of the potential weld defects and the stress concentration induced by weld reinforcement. The fracture risk in this position has seldom been assessed. Moreover, the pipelines are often exposed to complicated loading environments during the service period. Thus, the fracture responses of the pipelines with a crack at the weld toe and subjected to tension and internal pressure are considered in this study. A reference strain fracture assessment formulation is derived for the weld toe crack in welded clad pipelines. The formulation detailed expression form is determined by the extensive parametric finite element (FE) analyses and standard least square fitting method. The accuracy of the proposed formulation is validated by conducting a comparative study in J values attained from the formulation and FE analysis. Finally, a further study on extending the application range of the estimation formulation is carried out.

浅谈镍基合金625 + X60复合管焊接注意事项

浅谈镍基合金625 + X60复合管焊接注意事项

Evaluation of the Precipitation Process of a Clad Pipe by the Thermoelectric Potential Technique

The article reports a study carried out on metallic samples extracted from a metallurgically bonded clad pipe (API 5L X65 steel-Inconel 825 alloy) subjected to a solution heat treatment at 1200 °C and a subsequent aging treatment at 650 °C for different times in order to promote microstructural changes in thermo-metallurgical bonded materials. The non-destructive thermoelectric potential (TEP) technique was used to monitor microstructure changes due to the artificial aging process. In addition, micro-hardness tests were carried out on the metallic materials and micrographs were obtained by means of an optical and scanning electron microscope (SEM). The TEP value changed with solution treatment temperature and reached a maximum value for solution treatment at 1200 °C. The changes in TEP during solution treatment were caused by changes in the solubility of the alloying elements. In the artificial aging process, the TEP value decreased with increasing aging time due to the precipitation process, but exhibited distinct characteristics for the different zones at the clad pipe samples.

A strain-controlled fracture assessment for submarine thin-walled pipes with V-groove welds and circumferential embedded cracks

Abstract In the offshore industry, oil and gas are commonly transported with thin-walled clad pipes. Reel-lay is a widely used method to install clad pipes. During the installation and service process, engineering critical assessment (ECA) is usually required to guarantee safety. Most of the ECA methods pertain to surface cracks. The DNV-RP-F108 standard indicates that an embedded crack can be transformed into a surface crack in evaluation, and the result is still conservative. However, the evaluation can be over-conservative at times, meanwhile, the effect of the weld material as well as groove shape is not considered. In this work, a more direct assessment of welded clad pipes with a circumferential embedded crack is proposed based on a modified reference strain approach. A strain-controlled boundary condition is applied, and various pipe and weld geometrical shapes are considered in the analysis matrix. Two plugins based on Python script are developed to circularly create a lot of numerical models. Hundreds of regression analyses based on the linear relationship between normalized J integral and nominal strain are implemented. An analytical solution of the peak J integral of the embedded crack is proposed, and the solution is proved to be close to FEA.

A finite element based state-space approach for vibration analysis of slender explosive clad pipe with partial contact defect

Abstract An efficient modeling method is presented in this paper for vibration analysis of explosive clad pipe with partial contact defect (PCD). The principal purpose is to study the effects of the PCD on the vibration characteristics of explosive clad pipe and to explore effective techniques for detecting the PCD. The slender explosive clad pipe is regarded as two parallel elastic beams continuously joined by a virtual Winkler/Pasternak type viscoelastic layer, and the virtual layer is capable to describe the non-uniform bonding state such as the PCD. By means of finite element method and the standard linear solid (SLS) model, a state-space model of explosive clad pipe with inhomogeneous bonding state is developed for the fields of axial displacement and transverse displacement. The model can reflect the PCD pipe system under different boundary conditions and describe damping behavior of bonding interface. Experiments and numerical examples available in the literature demonstrate the accuracy and reliability of proposed approach. Finally, numerical results are presented and show that the PCD have significant effect on the natural frequencies and forced response in high-frequency domain. A potential method for identifying the length and position of the PCD in explosive clad pipe is also discussed in this paper.

Insights into the intergranular corrosion of overlay welded joints of X65-Inconel 625 clad pipe and its relationship to damage penetration

Intergranular corrosion (IGC) behaviors of X65-Inconel 625 clad pipe welded joints of different thickness (1.5, 2.0, 2.5 mm) were investigated. Corrosion tests showed that as the position of the specimen approached to the X65 side, the resistance of IGC decreased. The increased susceptibility of the welded joint to IGC was due to the small grain size and high Fe content. Different corrosion morphologies were observed in the base metal (BM) and heat-affected zone (HAZ), while corrosion penetrated differently into the interior of material. Pitting in the BM became deeper and evolved into inter-dendritic corrosion as the corrosion immersion test progressed.

Metallurgical Aspects in the Welding of Clad Pipelines—A Global Outlook

In the present work, the metallurgical changes in the welding of clad pipelines are studied. Clad pipes consist of a complex multi-material system, with (i) the clad being stainless steel or a nickel-based superalloy, (ii) the pipe being API X60 or X65 high-strength carbon steel, and (iii) the welding wire being a nickel-based superalloy or stainless steel in the root and hot pass, with a nickel or iron buffer layer, followed by filling with carbon steel wire. Alternatively, the corrosion resistant alloy may be used only. During production of the clad pipe, at the diffusion bonding temperature, substantial material changes may occur. These are carbon diffusion from the carbon steel to the clad, followed by the formation of hard martensite at the interface on cooling. The solidification behavior and microstructure evolution in the weld metal and in the heat-affected zone are further discussed for the different material combinations. Solidification behavior was also numerically estimated to show solidification parameters and resulting solidification modes.