Research and development of 3PP coating steel pipes

The industrial application of an exterior three-layer anticorrosive polypropylene coating system(3PP)on large-diameter(larger than Φ600 mm)steel pipes was developed using an experimental process simulation study and the optimization of raw materials inspection,steel pipe surface pretreatments,and water cooling control on a coating application process.The coating properties meet ISO standard 21809 on buried or submerged 3PP pipelines used in the petroleum and natural gas industries.Differential scanning calorimetry and X-ray diffraction were used to analyze the crystallinities and grain sizes of polypropylene(PP)top coats with different cooling rates.Increasing the melt cooling rate reduces the crystallinity and grain size of the PP top coat and enhances its strength and toughness.

Numerical Simulation Analysis of Welded Joints in Arch Ribs of Large Span Steel Pipe Arch Bridges

In order to study the residual stress distribution law of welded joints of arch ribs of large-span steel pipe concrete arch bridges,numerical simulation of temperature,stress and strain fields based on ABAQUS for welded joints of arch-ribbed steel tubes using 7-,8-and 9-layer welds is carried out and its accuracy is demonstrated.The steel pipe welding temperature changes,residual stress distribution,different processes residual stress changes in the law,the prediction of post-weld residual stress distribution and deformation are studied in this paper.The results show that the temperature field values and test results are more consistent with the accuracy of numerical simulation of welding,the welding process is mainly in the form of heat transfer;Residual high stresses are predominantly distributed in the Fusion zone(FZ)and Heat-affected zone(HAZ),with residual stress levels tending to decrease from the center of the weld along the axial path,the maximum stress appears in the FZ and HAZ junction;The number of welding layers has an effect on the residual stress distribution,the number of welding layers increases,the residual stress tends to decrease,while the FZ and HAZ high stress area range shrinks;Increasing the number of plies will increase the amount of residual distortion.

Theoretical and experimental study of the thermal strength of anticorrosive lined steel pipes

Bimetallic lined steel pipe （LSP） is a new anti-corrosion technology. It is widely used to transport oil, gas, water and corrosive liquid chemicals. At present, the hydroforming pressure for LSP has been investigated theoretically and experimentally by most researchers. However, there are a few reports on the thermal strength of bimetallic LSP. Actually, the bimetallic LSP will be subjected to remarkable thermal load in the process of three layer polyethylene （3PE） external coating. Reverse yielding failure may occur on the inner pipe of the bimetallic LSP when it suffers from remarkable thermal load and residual contact pressure simultaneously. The aim of this paper is to study the thermal load and strength of the bimetallic LSP. A mechanical model, which can estimate the thermal strength of the bimetallic LSP, was established based on the elastic theory and the manufacture of the bimetallic LSP. Based on the model, the correlation between the thermal strength of the bimetallic LSP and residual contact pressure and wall thickness of the inner pipe was obtained. Reverse yielding experiments were performed on the LSP （NT80SS-316L） under different thermal loads. Experiment results are consistent with calculated results from the theoretical model. The experimental and simulation results may provide powerful guidance for the bimetallic LSP production and use.

Effect of Pipe Diameter on Electrochemical Behavior of Stainless Steel Type 304 Pipes in Tap Water

We investigated the effects of pipe diameter on the corrosion resistance of stainless steel type 304 pipes using electrochemical measurements. Compared to plate steel, pipes have harder physical properties and tend to be harder and showed greater permeability with decreasing inner diameter. We found that the maximum corrosion current density in the secondary active state, which is the starting point of secondary passivation, appeared in the polarization curve measurement in tap water. Similar to the Vickers hardness and the maximum current density in the secondary active state, the permeability tended to increase as the diameter decreased. This is thought to increase the amount of deformation-induced martensitic and increase corrosion susceptibility. The peak of the secondary active current density was clearly seen as the potential sweep speed was increased. In addition, potential sweep speed dependence was observed in the corrosion susceptibility evaluation of deformation-induced martensite. In comparison with acid treatment, the formation of deformation-induced martensite was considered to occur in the extreme surface layer. The maximum corrosion current density in the secondary active state is expected to be a new susceptibility evaluation method for evaluating the deformation-induced martensitic transformation.

A Dynamics Study of a Magnetic Flux Leakage(MFL) Signal and its Application to Defect Location Discrimination in Steel Pipes MFL Testing Equipment

Difference processing was used to the direct current magnetic flux leakage （DC-MFL） signal, emanating from the defects machined artificially on the internal and external surfaces of a steel pipe. Consequently, the loea-tion discriminating index 8 was provided to identify the defect whether it is on the internal surface or the external one. Three characteristics, shape, depth and orientation of the defect, were discussed through a series of experiments on the artificial defects, such as transverse notches, oblique notches and pits on the steel pipe. The approach has been verified effective to address the defect location identifying problem, albeit the limits on the accuracy assessment to those natural defects on steel pipes in service.

Ultimate Bending Capacity of Strain Hardening Steel Pipes

Based on Hencky＇s total strain theory of plasticity,ultimate bending capacity of steel pipes can be determined analytically assuming an elastic-linear strain hardening material,the simplified analytical solution is proposed as well.Good agreement is observed when ultimate bending capacities obtained from analytical solutions are compared with experimental results from full-size tests of steel pipes.Parametric study conducted as part of this paper indicates that the strain hardening effect has significant influence on the ultimate bending capacity of steel pipes.It is shown that pipe considering strain hardening yields higher bending capacity than that of pipe assumed as elastic-perfectly plastic material.Thus,the ignorance of strain hardening effect,as commonly assumed in current codes,may underestimate the ultimate bending capacity of steel pipes.The solutions proposed in this paper are applicable in the design of offshore/onshore steel pipes,supports of offshore platforms and other tubular structural steel members.

Comparative study of weld residual stress on steel pipes with different weld types

This study developed a sequential coupling finite element procedure to predict residual stresses of steel pipes with longitudinal wela／ circumferential weld and spiral weld.The results show that the residual stress in heat affected zone（HAZ）is higher than that in weld for spiral weld pipe.For the circumferential weld pipe and spiral weld pipe,the residual stress in inner surface is higher than that in outer surface.However,for the spiral weld pipe,the residual stress in inner surface is smaller than that in outer surface.The hoop residual stress of circumferential weld pipe is higher than that of longitudinal weld pipe,while the axial residual stress of circumferential weld pipe is smaller than that of longitudinal weld pipe.The hoop stresses for circumferential weld pipe and axial stress for longitudinal weld pipe have exceeded the yield strength of base metal.With the increase of helix angle,the hoop stress decreases while the axial stress increases.For the spiral pipe（α=30° to 50°）,both the hoop stress and axial stress are relatively small.The spiral pipe（helix angle ranging from 30° to 50°） is helpful to reduce stress corrosion cracking（SCC） and it is recommended to manufacture the steel pipe.

Study of relieving weld residual stresses in large pressure steel pipes of hydropower station by local explosion treatment

From comparing the test of local explosion treatment(LET)with the locaf heat treatment (LHT)in welded plates and welded steel pipes in field,LET has excellent effect of stress relief and high efficiency. Whereas the effect of stress relief for LHT with 575℃×1.5hr is poor.The mechanical properties of welded joints after LET are basically the same as those of as-welded joints.The practically measuring results on 4 large steel-pipe surfaces indicate that the welding residual tensile stresses in welds,which mostly is compression residual stress,are basically relieved.

Alloy steel pipes and furnace tubes for petrochemical industry

The equipments and pipes serving at high temperature and pressure and the presence of hydrogen in the petrochemical industry are usually made of Cr-Mo steels.Cr9Mo pipes replacing Cr5Mo are widely used in many parts of/with high-sulfur crude oil refining equipment to meet the more demanding high temperature anticorrosion and oxidation resistance requirements.The mechanical property,creep rupture property and high temperature oxidation-resistant property of domestic Cr9Mo steel are at the same level as the similar foreign products.Three years applications indicate that domestic Cr9Mo steel can fully meet the service requirements of petrochemical industries.Finally,this paper presents the material selection guidelines for the key oil refining devices processing of low sulfur/high acid crude oil.

The Characterization of Damage of the Pipes Made from Stainless Steel

The damage was noted during the usage of the pipe system which was made out of austenite steel 316L on the assembly line for the production of urea. In order to find out the cause of such damage, the samples of pipes were taken at the places where the most damage took place. Samples were taken in the form of film, sediment and/or sludge from inner and the outer surface of the pipes. As well as each pieces of pipes were further cut into 10 mm x 10 mm plates. The prepared samples were studied using X-ray diffraction, X-ray emission spectrometry, scanning electron microscope and microanalysis as well as a light microscope. The results implicate microstructural changes within the inner wall of the pipe which was caused by intercrystalline corrosion. Such corrosion in the investigated samples of sediment and/or sludge appeared due to the damage of the protective film during the aggressive phases,

The Interlayer Stress Analysis of Polyethylene-steel Composite Pipes

Polyethylene-steel Composite Pipes is widely used in conveying corrosive media occasions,but the pipe may lose effectiveness in the process of transporting hot and cold media,so the research of stress distribution and variation in polyethylene-steel composite pipes is very necessary.This article first assume that a thin adhesive layer is in between the polyethylene and steel,the adhesive layer along the axial shear stress is the major cause of the polyethylene layer and the steel pipe off sticky.Secondly,we use a method of finite element to computer simulation by ANSYS,and verify initial assumptions.Finally,based on simulation data,we analyse the adhesive layer stress distribution and the variation with different parameters to change.Through the above research,preliminarily summarize the variation and distribution of interlaminar stress,and provide technical support for future design and process improvement of polyethylenesteel pipe.

Effect of microstructure on the low temperature toughness of high strength pipeline steels

Microstructure observations and drop-weight tear test were performed to study the microstructures and mechanical properties of two kinds of industrial X70 and two kinds of industrial X80 grade pipeline steels. The effective grain size and the fraction of high angle grain boundaries in the pipeline steels were investigated by electron backscatter diffraction analysis. It is found that the low temperature toughness of the pipeline steels depends not only on the effective grain size, but also on other microstructural factors such as martensite-austenite （MA） constituents and precipitates. The morphology and size of MA constituents significantly affect the mechanical properties of the pipeline steels. Nubby MA constituents with large size have significant negative effects on the toughness, while smaller granular MA constituents have less harmful effects. Similarly, larger Ti-rich nitrides with sharp corners have a strongly negative effect on the toughness, while fine, spherical Nb-rich carbides have a less deleterious effect. The low temperature toughness of the steels is independent of the fraction of high angle grain boundaries.

Experimental and analytical investigation on friction resistance force between buried coated pressurized steel pipes and soil

This paper presents an analytical approach for estimating frictional resistance to pipe movement at soil and external pipe surface of buried coated pressurized steel pipes relative to the internal thrust force.The proposed analytical method was developed based on 36 experiments,which involved three coating types(cement mortar(CM),polyurethane type-I(PT-I),prefabricated plastic tape(PPT))on pipes’surfaces,three different soils(pea-gravel(PG),sand(S),silty-clay(SC)),and four simulated over burden depths above the pipe’s crown.Investigation showed frictional resistance decreased with increasing over burden depth above the pipe’s crown.The degree of frictional resistance at the pipe-soil interface was found to be in the order of PG>SC>S for all coating variations and overburden depths.CM coated pipe buried in all three types of soil produced significantly higher frictional resistance as compared to other coating types.Based on experimental data,the developed analytical introduced a dimensionless factor“Z”,which included effects of types of coatings,soil,and overburden depths for simplified rapid calculation.Analysis showed that the method provided a better prediction of frictional resistance forces,in comparison to previous analytical methods,which were barely close in predicting friction resistance for different coating variations,soil types,and overburden depths.Friction resistance force values reported herein could be considered conservative.

Effect of Sacrificial Anode Protection for Steel Pipe Piles at Dandong Port

The sacrificial anode protection system for the steel pipe piles of the 3rd berth of Dandong; wharf at Dandong port has operated for eight years. In this paper, the program design and the protection effect of the sacrificial anode protection system are presented. The results of various inspections show that the piles are protected very satisfactorily.

Numerical study on forming complex fitting body on end of integrated stainless steel pipe without welds

It is necessary to use the integrated stainless steel pipe having two fitting bodies without welds while train travelling at high speed. In order to form this type of integrated stainless steel pipe, the method of preforming combined finish forming process is developed. The preforming process is characterized by flaring combined upsetting for left fitting body which is like a flange, and is characterized by tube axial compressive process under die constraint for right fitting body which is like a double-wall pipe. The finite element simulations of the processes are carried out by software package DEFORM, and the results indicate that: 1) left or right fitting body can be formed by a two-step forming process without folding and under-filling defects; 2) by using two-step forming, strain and stress in left fitting body are larger than those in right fitting body, and deformation in right fitting body is more homogenous than the deformation in left fitting body; 3) two or more preforming steps may be needed for left fitting body considering the distributions of strain and stress.

Development of pipeline steel at Baosteel over the last 20 years

This study reviews the development of Baosteel＇ s pipeline steel over the last 20 years. Energy demand accelerates the development of high-grade pipeline steel as well as modem petroleum and natural gas pipeline construction. Pipeline steel is a kind of typical modem microalloyed steel produced via thermo-mechanical controlled processing. The development process of pipeline steel at Baosteel represents the course of the technological progress of pipeline steel in China. In the last two decades, Baosteel＇ s pipeline steel has been developed from a single product of hot- rolled strips to a variety of products including hot-rolled strips, heavy plates, high-frequency electric resistance welded （HFW） pipes and U-ing-O-ing-Expanding （UOE） welded pipes. Moreover, the proportion of the HFW and the UOE welded pipes has been increasing year by year. UOE longitudinal submerged arc welding （SAW） pipes have become the leading product of strategic significance in Baosteel＇ s pipeline steel family. Over the last 20 years, Baosteel＇ s pipeline steel products have shifted from ＂ferrite ＋ pearlite＂ X52 to ＂acicular ferrite＂ XT0 and X80, and Baosteel has developed hydrogen-induced cracking （HIC） resistant pipeline steel. Baosteel＇ s pipeline steel products have been applied in variety of geographical areas,including deserts, Gobi, mountains,plains as well as the ocean. And both the X100 and the X120 ultra high strength pipeline steels have been produced on a trial basis. Baosteel has accumulatively produced 6.5 Mt of pipeline steel for both domestic and overseas projects. Baosteel will continue strengthening its strategic cooperation with oil companies, and conducting research on ultra high strength pipeline steel, pipeline steel for strain-based design and submarine pipeline steel,etc. , so as to meet the need of construction in the future.

Finite Element Analysis of the Steel Reinforced Plastic Pipe

The steel reinforced plastic pipe is a kind of green environmental protection pipelines with double-sides corrosionresisting and better withstanding to medium working pressure. The structure and technical process of this pipe are described briefly in this paper, and the finite element analysis has been done for the sake of understanding the distributions of stress and displacement inside this pipe under hydrostatic pressure. The analysis results are very important for safety application of the steel reinforced plastic pipe.

The Vibration Controllability of 20~# Steel Pipe Excited by Unsteady Flow

An excited experiment system of 20# steel pipe was established with oil cylinder, 20# steel pipe, frequency converter, pump station and wave exciter generating unsteady flow artificially. The experimental results showed that the 20# steel pipe could vibrate with the excitation of unsteady flows, and the vibration was periodic, instead of a harmonic one. Particles on the front and rear positions of pipe vibrated synchronously, and the vibration intensity of the pipe＇s two ends was greater than in the middle. System pressure and wave exciter＇s frequency had much influence upon pipe＇s amplitude. Pipe＇s vibration frequency was little affected by system pressure, and its value was close to the wave exciter＇s. Therefore, the active control of pipe＇s vibration can be realized by setting system pressure and adjusting frequency converter＇s frequency.

Finite Element Analysis of Modeling Residual Stress Distribution in All-position Duplex Stainless Steel Welded Pipe

On the basis of the thermal-elastic-plastic theory, a three-dimensional finite element numerical simulation is performed on the girth welded residual stresses of the duplex stainless steel pipe with ANSYS nonlinear finite element program for the first time. Three-dimensional FEM using mobile heat source for analysis transient temperature field and welding stress field in circumferential joint of pipes is founded. Distributions of axial and hoop residual stresses of the joint are investigated. The axial and the hoop residual stresses at the weld and weld vicinity on inner surface of pipes are tensile, and they are gradually transferred into compressive with the increase of the departure from the weld. The axial residual stresses at the weld and weld vicinity on outer surface of pipes is compressive while the hoop one is tensile. The distributions of residual stresses compared positive-circle with negative-circle show distinct symmetry. These results provide theoretical knowledge for the optimization of process and the control of welding residual stresses.

Manufacture of Extra-Thin Wall Steel Pipe by LD Cluster Mill

The manufacture of extra-thin wall steel pipe by LD cluster mill through suitable tool design and process design was described in detail.The defects in steel pipe produced during rolling were analysed and some measures were taken to improve them.Five kinds of extra-thin wall steel pipes have been produced successfully,which are as follows:φ18.5mm×0.25 mm,φ15.5mm×0.25 mm,φ11.4mm×0.2mm,φ14- 24mm×0.12 mm,φ21.74mm×0.12 mm.