Study on Correlation Between Process Defect and Mechanical Properties of Polyethylene Pipe Elector⁃fusion Joints

doi:10.19491/j.issn.1001-9278.2021.09.010

Abstract

Abstract:

An ultrasonic phased array detection technology was proposed to measure the edge width （l） of Heat Affected Zone（HAZ） of polyethylene pipe elector?fusion joints under different welding time （t）. The percentage of brittle peel， composition of functional groups and crystallinity （X_c） were measured by extrusion peel， FTIR and DSC， and then the relationship between （l） and welding performance （H_c） was established to realize the non?destructive testing of the elector?fusion joint. The results indicated that the HAZ was moved to the outer wall in an exponential growth trend with an increase in welding time. The welding performance of the joint was improved first and then tended to decrease. When t=50 s， l=2.21 mm， X_c=53.03 %， thewelding performance reached a maximum value of 96.21 %. When t<40 s， l and X_c were slightly lower， and there were cold welding defects on the joint. In contrast， when t>70 s， there were dislocation and fusion on the metal wire in the melting zone of the joint appears. The over?welding defects also took place on the joints due to a high?temperature oxidation reaction. Both of two defects led to a decrease in the joint welding performance.

Key words: ultrasonic phased array detection technology, polyethylene pipe, elector?fusion joint, process defect, welding performance

CLC Number:

TQ325.1⁺2

WANG Zhigang, YANG Bo, LI Zhi, PENG Guoping, JIANG Zaijia, LI Guanbao. Study on Correlation Between Process Defect and Mechanical Properties of Polyethylene Pipe Elector⁃fusion Joints[J]. China Plastics, 2021, 35(9): 64-68.

Figures/Tables 9

Fig.1. Principle diagram of polyethylene pipe elector?fusion joins

Fig.2. The preformed elector?fusion join specimens and its phased array characteristic atlas

Fig.3. The relationship between the welding time t and the width l of the bubble characteristic line of polyethylene pipe elector?fusion joins

Fig.4. The extrusion stripping test drawing of polyethylene pipe elector?fusion joins

Fig.5. The extrusion stripping test results of polyethylene pipe elector?fusion joins after different welding time

焊接时间/s	热影响区边缘宽度l/mm	脆性剥离百分比C_c/%	焊接性能H_c/%	缺陷类型
10	0	100	0	冷焊
20	1.01	100	0	冷焊
30	1.37	22.88	77.12	冷焊
40	1.63	10.00	90.00	正常
50	2.21	3.79	96.21	正常
60	2.28	10.14	89.86	正常
70	2.45	22.95	77.05	过焊
80	2.60	30.58	69.42	过焊
90	3.02	35.86	64.14	过焊

Tab.1. The relationship between the edge width l of the HAZ and the joint welding performance Hc of the joint after different welding time

Fig.6. DSC curves of polyethylene molecules on the joint fusion surface after different welding time

Fig.7. The relationship between the crystallinity Xc and the welding time t of the polyethylene molecule on the joint fusion surface

Fig.8. The composition of polyethylene molecular functional groups on the fusion surface of the joint after different welding time

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