Evaluation of Slow Crack Growth Resistance for Polyethylene Pipe Butt-Fusion Welded Joint

doi:10.19491/j.issn.1001-9278.2020.09.009

Abstract

Abstract:

The strain-hardening test was adopted to evaluate the slow crack growth (SCG) resistance of polyethylene (PE) pipe butt-fusion welded joint under different welding processes. The variation rule for the SCG resistance of PE pipe butt?fusion welded joint was analyzed under different welding process parameters by establishing a welding temperature gradient between 190 and 250 °C, a welding stress gradient between 0.6 and 1.4 MPa, and an endothermic time gradient between 40 and 140 s. The effects of cold-welding and over-welding defects on the SCG resistance of PE pipe joint were investigated. The results indicated that the welding temperature, welding pressure and the endothermic time were all the important process parameters that influenced the SCG resistance of the PE pipe butt-fusion welded joints, and the optimum welding parameters could be determined as 220 °C, 1 MPa and 100 s for the PE 100 pipe (d_n110, SDR11). The selection of lower or higher welding parameters could result in the formation of cold-welding or over-welding defects in the pipe joint, thus reducing the SCG resistance.

Key words: polyethylene, pipe, strain hardening, welding process, butt-fusion, welded joint, slow crack growth

CLC Number:

TQ320.72⁺4

WANG Zhigang, YANG Bo, WANG Jingran, XU Qingyong, SHEN Yang. Evaluation of Slow Crack Growth Resistance for Polyethylene Pipe Butt-Fusion Welded Joint[J]. China Plastics, 2020, 34(9): 51-55.

Figures/Tables 10

Fig.1. Schematic diagram of polyethylene pipe slow crack growth

Fig.2. Tensile curve of strain hardening test

Fig.3. The prepared test samples

Fig.4. Strain hardening of the butt?fusion welded joints at different welding temperature

编号	焊接温度/℃	应变硬化模量/MPa	标准偏差	缺陷类型
1	190	49.64	1.257 4	冷焊
2	210	52.71	0.530 8	正常
3	220	53.77	0.363 3	正常
4	230	58.98	0.302 5	正常
5	250	40.78	1.137 5	过焊

Tab. 1. Strain hardening of the butt?fusion welded joints at different welding temperature

Fig.5. Infrared spectrum of pipe joint surface welded at 230~250 ℃

Fig.6. Strain hardening trend of the butt?fusion welded joints in different welding stress

编号	焊接压力/MPa	$应变硬化模量$ /MPa	标准偏差	缺陷类型
1	0.6	39.18	0.990 7	冷焊
2	0.8	57.50	0.660 8	冷焊
3	1.0	59.33	0.830 2	正常
4	1.2	46.08	0.690 7	过焊
5	1.4	39.03	1.059 3	过焊

编号	焊接压力/MPa	$应变硬化模量$ /MPa	标准偏差	缺陷类型
1	0.6	39.18	0.990 7	冷焊
2	0.8	57.50	0.660 8	冷焊
3	1.0	59.33	0.830 2	正常
4	1.2	46.08	0.690 7	过焊
5	1.4	39.03	1.059 3	过焊

Tab.2. Strain hardening of the butt?fusion welded joints in different welding stress

Fig.7. Strain hardening trend of the butt?fusion welded joints in different endothermic time

编号	吸热时间/s	$应变硬化模量$ /MPa	标准偏差	缺陷类型
1	40	43.32	1.253 9	冷焊
2	70	55.10	1.008 7	冷焊
3	100	58.99	0.653 2	正常
4	120	58.74	0.486 4	过焊
5	140	44.55	0.838 4	过焊

编号	吸热时间/s	$应变硬化模量$ /MPa	标准偏差	缺陷类型
1	40	43.32	1.253 9	冷焊
2	70	55.10	1.008 7	冷焊
3	100	58.99	0.653 2	正常
4	120	58.74	0.486 4	过焊
5	140	44.55	0.838 4	过焊

Tab. 3. Strain hardening of the butt?fusion welded joints in different endothermic time

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