External Corrosion Analysis of Gas Pipeline Based on Gray Prediction Models

X70 steel gas transmission pipeline has a large market share and a long operation time, and the problem of pipeline integrity, represented by corrosion, is now becoming increasingly prominent. Under actual working conditions, the corrosion of gas transmission pipelines is complex. In order to study the corrosion characteristics of X70 steel gas transmission pipeline under different soil environments, help pipeline integrity management and ensure operational safety, the raw gas pipeline of an LNG project was used as the object of study, and firsthand data were obtained with the help of OLYMPUS 38DL PLUS thickness gauge with the help of special hanging sheet deployment mode on site. The data were brought into a suitable gray prediction model to detect trends in condition data and to predict future corrosion levels. Finally, a sampling inspection plan with the best combination of time and cost was obtained. The results are as follows: 1. The trend in the corrosion data exhibits a typical single-peak sequence, coupled with the "S"-shaped growth characteristics of biological growth, which ultimately reveals that SRB is the main cause of pipeline corrosion; 2. Among the uncoated original state hangings, the greatest corrosion depths can be observed in 2018 and 2019, with the greatest change in corrosion depth in 2020. 3. The best Verhulst model is with cumulative corrosion depths of 249.00 μm and 250.61 μm for the next 2 years. The next step is to perform a full inspection of 50 uncoated original hanging pieces, while performing sampling inspection of 15 three-layer PE parcel pieces will improve the integrity of the pipeline.