16. 20℃, 50-year confidence lower limit (σLCL):
A stress value used to evaluate material performance, which refers to the confidence lower limit of the predicted long-term strength of the pipe made of the material under internal water pressure at 20℃ and 50 years with a confidence level of 97.5%, in MPa.
17. Long-term hydrostatic strength (σLTHS):
Indicates the average strength predicted at temperature T and time t (the average strength refers to the confidence lower limit of the material strength when the confidence level is 50%), in MPa.
18. 20℃, 50-year long-term strength (σLTHS):
The average strength or predicted average strength of the pipe under water pressure at 20℃ for 50 years, in MPa.
19. Environmental stress cracking:
The phenomenon of accelerated stress cracking due to environmental conditions. The environmental stress cracking resistance of the material is often expressed by ESCR.
20. Degree of crosslinking:
A physical quantity indicating the degree of crosslinking. When cross-linking occurs between polymer chains, it is expressed as the average number of cross-linking units per polymer molecule. It is also called cross-linking point density and cross-linking index. It is usually expressed by gel content.
21. Ductile failure:
Destruction accompanied by obvious awakening deformation.
22. Brittle failure:
Destruction without obvious plastic deformation in the rupture area.
23. Penetration failure:
A form of failure in which the pressurized fluid in the pipe seeps out of the pipe wall to form visible loss but no obvious cracking occurs.
24. Hoop stress:
Stress along the circumference of the pipe caused by internal pressure in the pipe wall.
25. Burst pressure:
The maximum pressure before the pipe ruptures in the hydrostatic burst test of the pipe.
26. Failure temperature:
The highest temperature that occurs when the pipeline system exceeds the control limit.
27. Structural wall pipe:
A general term for pipes with composite wall structures composed of multiple layers of materials and pipes with special-shaped wall structures such as open ribs, closed ribs (hollow), etc.
28. Special-shaped wall pipe:
A general term for pipes with smooth inner wall and spiral, annular or ribbed outer wall.
29. Double-wall corrugated pipe:
The inner wall is smooth and flat, the outer wall is trapezoidal or arc-shaped corrugated ribs, and the inner and outer wall corrugations are hollow special-shaped pipes.
