Pipeline bear the effects of the pipeline transmission medium pressure and temperature, but also suffer from a variety of delivery through the heart of the impact of natural and human factors that may occur in the course of leaking or breaking all sorts of accidents. Not only due to leakage of pipeline accidents affect transport caused economic losses, but also pollute the environment. To ensure the safe operation of the pipeline and generate pipeline accident prevention should be the design, construction and operation of three aspects, including design and reasonable choice of pipe is very important. As for the pipe, the strength, toughness and weldability are three basic quality standards. It should also consider the environmental and transport medium for pipe corrosion, corrosion-resistant steel choice.
(1) Mechanical properties: The main indicator to measure the mechanical properties of the pipe have strength, yield limit, elongation, etc.
① Tensile strength: tube in a tensile test, when a sample corresponding to the maximum stress of pulling off.
② Yield strength: steel in tensile test, the specimen tensile deformation, when excluding the initial transient effect flexor, the minimum stress in the service phase.
③ Elongation: a measure of shaping steel refers to steel in the tensile test, the sample is drawn off, and the elongation percentage of the original distance of the standard gauge.
④ Bauschinger effect: metal or alloy to produce pre-loaded micro plastic deformation after unloading and then increased with the elastic limit of the load, reverse load is reduced elasticity of the elastic limit is not complete phenomenon.
(2) Fracture toughness: Pipeline rupture can be divided into fracture and brittle fracture toughness
① Ductile fracture: the gradual expansion and eventually rupture caused by tiny cracks in the conditions of excessive tensile stress and cracks exist simultaneously.
② Brittle fracture: the temperature, stress and cracks caused by the combined effect of three conditions, the fracture is often much lower than earlier in the yield stress under conditions of a sudden.
③ Fracture toughness: energy and the ability to attribute the deformation of metallic materials with crack before breaking absorption.
④ Ductile-brittle transition temperature: at a certain temperature range, fracture toughness just with the use of lower temperatures.
Reduced. When a temperature near Avenue frontage temperature, there will be a sudden drop in toughness phenomenon, the steel from breaking into brittle fracture toughness, this temperature is called steel ductile-brittle transition temperature.