Performance Evaluation of Polyamide-12 Pipe Serviced in Acid Oil and Gas Environment

To study the compatibility of PA12 with oil and gas medium, the exposure test was carried out by the HTHP autoclave under the simulated medium environment of oil and gas fields. At different exposure periods (test period is 0/1/3/5/7 week(s)) in different temperatures (60 and 90 °C), the physical properties of the samples before and after the test, such as weight and tensile strength were investigated. And then the applicability of the pipes in the simulated medium environment was evaluated comprehensively by analyzing the changes of the micro-morphology and composition of the samples. Compared with the original samples, the weight of samples after test did not change significantly with the average rate of 1.1 to 2.4% at 60 °C, while 1.3 to 3.0% at 90 °C. The yield strength showed a downward trend during the exposure test. In the early stage of exposure (0–3 weeks), the temperature had little effect on the tensile properties, but with the increase of exposure time (3–7 weeks), the effect became more obvious. When the exposure time reaches 7 weeks, the corresponding yield strength at 60 °C is 27.65 MPa, while 27.29 MPa at 90 °C, which is 27.01 and 27.96% lower than the yield strength of the original sample (37.88 MPa), respectively. According to the microscopic morphology analysis, there are cracks on the surface of the specimen under the simulated working conditions. The infrared analysis shows no change in the composition of the sample after immersion compared with the original one, and no damage to the composition and structure of the sample after the exposure test. The above analyses show that the service performance of PA12 pipes is reduced due to penetration and swelling.