Oxidation induction time pipes

Figure 2. Oxidation induction time (OIT not the log-scale) for samples taken at a certain depth (0.9-1.0 mm from the inner wall from PB pipes pressure-tested at 90 C with internal chlorinated water (0.5, 1.0 and 1.5 ppm Cl) as a function of the exposure time. The line is a linear fit of the data. The insert figure shows the results of extrapolation to 01T= 1 min based on OIT data from exposures shorter than tfnax- From Lundback et al.(12) and with permission from Elsevier, UK.

Oxidative induction time (OIT) provides an index useful in comparing the relative resistance to oxidation of a variety of hydrocarbon materials. The OIT procedure was first developed in 1975 by Gilroy and coworkers at Bell Laboratory as a test procedure to screen polyethylene insulation used in telephone wire and cable for its oxidation resistance. The method first became available as a Western Electric Specification and later as ASTM Test Method for Copper-Induced Oxidative Induction Time of Polyolefins. Polyolefin manufacturers quickly embraced the procedure and began to apply it to other applications including raw resins, finished pipes, wire and cable insulation, and, most recently, geosynthetic waste pit liners (ASTM D3895 2009). 

EN 728 Polyolefin pipes and fittings - determination of oxidation induction time. 

Right Influenoe of stabilizer extraction on oxidative induction times (on internal pipe surfaoe) of a PE-HD pipe as a function of exposure time in water at 80°C with 0.05% type A and B antioxidants, respectively [181]... 

DIN EN 728 [445] Plastics piping and ducting systems - Polyolefin pipes and fittings -Determination of oxidation induction time German version EN 728... 

Oxidation induction times at 200 °C fora PB pipe (63 5.6 mm) as a function of distance from the interior waii [829]... 

Figure 5.287 shows that the profiles for the viscosity index and the oxidation induction time i.e., degradation, of pipes in internal pressure creep tests is independent of internal pressure. One of two pipes exposed to 4 N/mm broke after 8,208 h, while the other one broke after 1,442 h, 3,720 h, and 13,690 h in the second case, the pipe was reinstalled and reloaded at 4 N/mm after elimination of the failure area [181]. 

Figure 5.288 shows the reduction in oxidation induction time (Oil) during a inter-nai pressure creep rupture test. The initiai OIT values are approximately proportional to the amount of antioxidant however, degradation onset can be influenced only in part by the amount of antioxidant, because stabilizer concentration on the pipe surface is decisive for failure [181]. 

Pipes of HOPE were exposed to chlorinated water at elevated temperatures. The materials were stabilised with hindered phenols and phosphites [47]. Measurement of the oxidation induction time... 

Alia- testing, the following test methods were performed on the selected tested specimens Visual examination of the specimens was performed to identify the modes of failure. Oxidation induction time (OIT) was performed in general accordance with ISO 11357-6-2002 (E) [10] at 200 °C. Specimens wo-e taken liom the inner and outer surfaces as well as liom the bulk pipe wall and Micro-attenuated total reflection Fourier Transform Infrared Spectroscopy (micro-ATR) was performed. The inner surface and the fracture surface were examined. Scaiming Eleetron Microscopy (SEM) coupled with Energy Dispersive X-ray analysis (EDX) was performed on the iimer surface and the fiacture surface. 

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