Pipeline Mending Corrosion Hot Melt Adhesive Bonding And Aging Properties

To ensure the safety of oil and gas transmission, underground pipeline mendings are protected by 3PE. According to the online surveies of CNPC and related reports, coating failure exists in underground pipelines, which is caused by the poor wetting of the melt on substrates,low initial bond strength and poor mobility at construction condition. Hot melt adhesive with high bonding strength and good melt fluidity is expected by selecting and compounding EVA resins, studies of the amount of tackifier and plasticizer and applying blending modification. Which is practically benefit for guaranteeing safety and controlling costs.The melting processes of different hot melt adhesives and their components are examined by differential scanning calorimetry (DSC), which shows starting melting temperatures (Ts) keep constant, but ending melting temperatures (Tf) increase, as average molecular weight of EVA increases. Viscosity of hot melt adhesive increases, but activation energy of viscous flow decreases, with average molecular weight of EVA increasing, tested by capillary rheometer. The strengths of shear failure and debond of each hot melt are measured by micro-electronic controlled testing machine, which shows Er increases but Ep decreases as average molecular weight increases. Rh and distribution of each EVA are characterized by dynamic light scattering (DLS). We calculate the Molar molecular weight range of motor coil units with better overall performances in molten state according to polymer entanglement theory. Finally, EVA900 and EVA7720 are selected as complex matrixes.Orthogonal test identifies the most sensitive factor for Eτand Eρis the amount of rosin and the most sensitive factor forηa is the amount of paraffin, through which the optimal constitution A3BC1 is fixed. Add EVA-g-MA to A3B2C1 to increase the polarity of its melt. With the amount of EVA-g-MA increasing, Eτandηa increase, but Eρincreases firstly and then decreases. The melt reveals optimal overall performances with shear failure strength(Eτ) 2.99MPa,debonding strength(Eρ)72.35N/cm and good flowing property:apparent viscosity (ηa)512.6Pa·s at the state of 90℃and pressure of 20 kg, when about 15 unit EVA-g-MA is added.Thermal oxidative aging tests suggest Eτof the melt unchanged, and TGA demonstrate the temperature of weight loss of the melt above 300℃, which indicates EVA hot melt has an excellent anti-thermal-oxidative-aging property. Corrosion tests show with etching time extending, Et of hot melt in alkaline medium reduces significantly. Experiments illustrate EVA and EVA-g-MA mixtures are susceptible to hydrolysis. In summary, we conclude that the melt ageing is a result of hydrolysis reaction, rather than caused by thermal oxidative aging.