Study and Evaluation of Advanced TOFD Method for Inspection of Polyethylene Pipes but Welding

Polyethylene material has some specification that makes very difficult any kind of inspection based on ultrasonic. The acoustic impedance and sound velocity in this kind of material are near to the materials commonly used in ultrasonic wedges. Also this kind of materials are highly attenuative materials for ultrasound. To inspection of polyethylene circumferential but welds and overcome to all the problems mentioned, the especial technique of TOFD （Time of Flight Diffraction） method which employs low frequency probe and concentrate on the inspection area that longitudinal waves turn into transverse waves has been used. The purpose of inspection is determining the exact location of surface and internal welding defects. For this purpose, two separate polyethylene pipes with 10 inch in diameter, 15 mm thickness and also 25 inch diameter, 28 mm thickness, were selected. In total 40 artificial defects which involve 28 side drill holes in deferent depths and 12 surface and sub-surface notches were created. All artificially created defects were detected with very good accuracy. Unlike the conventional TOFD method which have 2 to 3 mm dead zone, by using the above method even surface notch with 0.5 mm has been detected.

Detection of internal crack growth in polyethylene pipe using guided wave ultrasonic testing

Despite the success of guided wave ultrasonic inspection for internal defect detection in steel pipes,its application on polyethylene(PE)pipe remains relatively unexplored.The growth of internal cracks in PE pipe severely affects its pressure-holding capacity,hence the early detection of internal cracks is crucial for effective pipeline maintenance strategies.This study extends the scope of guided wave-based ultrasonic testing to detect the growth of internal cracks in a natural gas distribution PE pipe.Laboratory experiments and a finite element model were planned to study the wave-crack interaction at different stages of axially oriented internal crack growth with a piezoceramic transducer-based setup arranged in a pitch-catch configuration.Mode dispersion analysis supplemented with preliminary experiments was performed to isolate the optimal inspection frequency,leading to the selection of the T(0,1)mode at 50-kHz for the investigation.A transmission index based on the energy of the T(0,1)mode was developed to trace the extent of simulated crack growth.The findings revealed an inverse linear correlation between the transmission index and the crack depth for crack growth beyond 20%crack depth.

Lateral compression and energy absorption of foamed concrete-filled polyethylene circular pipe as yielding layer for high geo-stress soft rock tunnels

Foamed concrete as energy absorption material for high geo-stress soft rock tunnels has been proven to be feasible due to its high compressibility and lightweight.However,the lengthy curing and defoaming problems caused by the cast-in-place method of large-volume foamed concrete remain unsolved.In this study,we propose a novel energy absorber composed of foamed concrete-filled polyethylene(FC-PE)pipe and analyze its deformation and energy absorption capacity via quasi-static lateral compression experiments.Results show that FC-PE pipes exhibit typical three-stage deformation characteristics,comprising the elastic stage,the plastic plateau,and the densification stage.Furthermore,the plateau stress,energy absorption,and specific energy absorption of the specimens are 0.81–1.91 MPa,164–533 J,and 1.4–3.6 J/g,respectively.As the density of the foamed concrete increases,the plateau stress and energy absorption increase significantly.Conversely,the length of the plastic plateau and energy absorption efficiency decrease.Moreover,based on the vertical slice method,progressive compression of core material,and the 6 plastic hinges deformation mechanism of the pipe wall,a theoretical calculation method for effective energy absorption is established and achieves good agreement with experimental results,which is beneficial to the optimization of the composite structure.

Study on fracture characteristic of welded high-density polyethylene pipe

Crack opening displacement(COD) was applied to characterize the fracture initiation of the tough high density polyethylene. Normal single side notched three point bend specimens and silica rubber replica techniques were used to study the characteristic COD of high density polyethylene pipe and its butt fusion joints including the weld fusion zone and heat affected zone at different temperature from -78 ℃ to 20 ℃ . Testing results show that the characteristic COD appears to depend on the structural features that are determined by welding process and the testing temperature. As the temperature is lowered, the characteristic COD of all zones studied decreases. Because the welding process significantly changes some structural feature of the material, characteristic COD of the weld fusion zone is the smallest one among those of the three zones. The results can be used for the engineering design and failure analysis of HDPE pipe.

A review of nondestructive examination technology for polyethylene pipe in nuclear power plant

Polyethylene （PE） pipe, particularly high- density polyethylene （HDPE） pipe, has been successfully utilized to transport cooling water for both non-safety- and safety-related applications in nuclear power plant （NPP）. Though ASME Code Case N755, which is the first code case related to NPP HDPE pipe, requires a thorough nondestructive examination （NDE） of HDPE joints. However, no executable regulations presently exist because of the lack of a feasible NDE technique for HDPE pipe in NPP. This work presents a review of current developments in NDE technology for both HDPE pipe in NPP with a diameter of less than 400 mm and that of a larger size. For the former category, phased array ultrasonic technique is proven effective for inspecting typical defects in HDPE pipe, and is thus used in Chinese national standards GB/T 29460 and GB/T 29461. A defect- recognition technique is developed based on pattern recognition, and a safety assessment principle is summa- rized from the database of destructive testing. On the other hand, recent research and practical studies reveal that in current ultrasonic-inspection technology, the absence of effective ultrasonic inspection for large size was lack of consideration of the viscoelasticity effect of PE on acoustic wave propagation in current ultrasonic inspection technology. Furthermore, main technical problems were analyzed in the paper to achieve an effective ultrasonic test method in accordance to the safety and efficiency requirements of related regulations and standards. Finally, the development trend and challenges of NDE test technology for HDPE in NPP are discussed.