Plastic limit load analysis for pressure pipe with incomplete welding defects based on the extended Net Section Collapse Criteria

With von Mises yield criterion,the loading range of Net Section Collapse(NSC) Criteria is extended from combined tension and bending loadings to combined bending,torsion and internal pressure loadings.A new theoretical analyzing method of plastic limit load for pressure pipe with incomplete welding defects based on the extended NSC Criteria is presented and the correlative formulas are deduced,the influences of pipe curvature,circumferential length and depth of incomplete welding defects on the plastic limit load of pressure pipe are considered as well in this method.Meanwhile,according to the orthogonal experimental design method,the plastic limit loads are calculated by the finite element method and compared with the theoretical values.The results show that the expressions of plastic limit load of pressure pipe with incomplete welding defects under bending,torsion and internal pressure based on extended NSC criteria are reliable.The study provides an important theoretical basis for the establishment of safety assessment measure towards pressure pipe with incomplete welding defects.

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.

Extreme Pressure Equipments

Pressure equipments in the process industries and the newly developing industries usually have extreme sizes and/or are subjected to extreme operating conditions such as high pressure,blast loading,cryogenic temperature,elevated temperature,complex corrosion,and so on.In order to understand,research and develop these equipments systematically,a concept of extreme pressure equipments（EPEs） is proposed.The applications and demands of EPEs in petrochemical industry,coal chemical industry,advanced energy,military,space technology,and environment protection are introduced.Basic scientific problems in material,design,inspection, and safety related to EPEs are discussed.Then,take chemical composition,manufacturing process,service duration,and operating conditions for example,main factors which affect material properties of EPEs are analyzed.New design concepts including design based on life cycle,dynamic design and light-weight design are introduced.EPEs with higher efficiency,lower cost and safer performance are in urgent demand in national major projects including ten million ton oil refinery,one million ton ethylene,liquefied natural gas transportation,and nuclear power plant.Thus,further research should be conducted on information acquisition, multi-mechanism damage coupling model,damage inspection,life prediction,online safety monitoring,maintenance strategy,safety pre-warning system,and emergency system.

Effect of strength matching on the reliability of welded pipe with circumferential surface crack

For different strength matching, the reliability index and failure probability of welded pressure pipe with circumferential surface crack were calculated using three dimensional stochastic finite element method. This method has overcome the shortcomings of conservative results in safety assessment with deterministic fracture mechanics method. The effects of external moment and the depth of the circumferential surface crack (a) on the reliability of pressure pipe were also calculated and discussed. The calculation results indicate that the strength matching has certain effect on the reliability of the welded pressure pipe with circumferential surface crack. The failure probability of welded pressure pipe with high strength matching is lower than that with low strength matching at the same conditions. The effects of strength matching on the failure probability and reliability index increased by adding external moment (M) and the depth of the circumferential surface crack (a).

Design,Manufacture and Maintenance of Pressure Equipment Based on Accidents Survey

Most of the important units of pressure equipment have been manufactured successfully in China related to the national key construction projects,such as 10 million tons/year oil refinery,million tons/year ethylene,large coal chemical,etc.However,some of them failed to operate shortly after their putting into service.Some suffered severe damage even during the previous period of manufacture and installation.In this paper,cases of accident survey and failure analysis are given for some typical pressure vessels.It is found that many accidents are related to insufficient consideration of the design and manufacture of the equipment.These accidents occur fundamentally because of the Chinese design standards codes for pressure equipment without risk or life concepts and the support from a database for potential risk existing in their dynamic service.Most designers and manufacturers are unable to make correct design,materials selection and manufacturing process all due to a lack of engineering experience.In order to avoid the repetition of the accidents and improve the safety,reliability and economy of pressure equipment,a platform is suggested for design,manufacture and maintenance of pressure equipment in China based on accidents survey.In other words,some effective precautionary measures are taken at the design and manufacture stage,and the design methodology has to be based on service life requirement and desirable risk level.At the service stage some reasonable inspection/monitoring approaches should be utilized to control risks and ensure the equipment operating safely until its desired lifespan.Finally,the basic scheme and some key technologies are briefly given for the platform construction.The concept of risk and life based design,manufacture and maintenance proposed herein has important significance for improving and perfecting the codes and standards for design,manufacture and maintenance of Chinese pressure-bearing equipment,enhancing the life and reliability of Chinese pressure-bearing equipment and promoting the development of in-service maintenance technology that combines safety and economy.

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.

Flow field and pressure loss analysis of junction and its structure optimization of aircraft hydraulic pipe system

The flow field in junction is complicated due to the ripple property of oil flow velocity and different frequencies of two pumps in aircraft. In this study, the flow fields of T-junction and Y-junction were analyzed using shear stress transport （SST） model in ANSYS/CFX software. The simulation results identified the variation rule of velocity peak in T-junction with different frequencies and phase-differences, meanwhile, the eddy and velocity shock existed in the corner of the T-junction, and the limit working state was obtained. Although the eddy disappeared in Y-junction, the velocity shock and pressure loss were still too big. To address these faults, an arc-junction was designed. Based on the flow fields of arc-junction, the eddy in the junction corner disappeared and the maximum of velocity peak declined compared to T-and Y-junction. Additionally, 8 series of arc-junction with different radiuses were tested to get the variation rule of velocity peak. Through the computation of the pressure loss of three junctions, the arc-junction had a lowest loss value, and its pressure loss reached the minimum value when the curvature radius is 35.42 mm, meanwhile, the velocity shock has decreased in a low phase.

New model for standpipe pressure prediction while drilling using Group Method of Data Handling

The continuous evaluation of the measured Stand Pipe Pressure(SPP)against a modeled SPP value in real-time involves the automatic detection of undesirable drilling events such as drill string washouts and mud pump failures.Numerous theoretical and experimental studies have been established to calculate the friction pressure losses using different rheological models and based on an extension of pipe flow correlations to an annular geometry.However,it would not be feasible to employ these models for real-time applications since they are limited to some conditions and intervals of application and require input parameters that might not be available in real-time on each rig.In this study,The Group Method of Data Handling(GMDH)is applied to develop a trustworthy model that can predict the SPP in real-time as a function of mud flow,well depth,RPM and the Fan VG viscometer reading at 600 and 300 rpm.In order to accomplish the modeling task,3351 data points were collected from two wells from Algerian fields.Graphical and statistical assessment criteria disclosed that the model predictions are in excellent agreement with the experimental data with a coefficient of determination of 0.9666 and an average percent relative error less than 2.401%.Furthermore,another dataset(1594 data points)from well-3 was employed to validate the developed correlation for SPP.The obtained results confirmed that the proposed GMDH-SPP model can be applied in real-time to estimate the SPP with high accuracy.Besides,it was found that the proposed GMDH correlation follows the physically expected trends with respect to the employed input parameters.Lastly,the findings of this study can help for the early detection of downhole problems such as drill string washout,pump failure,and bit balling.

Limit Analysis of Defect-Free Pipe Elbow Under Internal Pressure With Mean Yield Criterion

With mean yield（MY）criterion,an analytical solution of the collapse load for a defect-free pipe elbow under internal pressure is first obtained.It is a function of ratio of thickness to radius t0/r0,strain hardening exponent n,curvature influence factor mand ultimate tensile strength.The collapse load increases with the increase of m,and it is the same as the burst pressure of straight pipe if m=1is assumed.The MY-based solution is compared with those based on Tresca,Mises and twin shear stress（TSS）yield criteria,and the comparison indicates that Tresca and twin shear stress yield criteria predict a lower bound and an upper bound to the collapse load respectively.However,the MY-based solution lies just between the TSS and Tresca solutions,and almost has the same precision with the Mises solution.