Session: 14-01-01: General Topics on Risk, Safety, and Reliability I

Paper Number: 148745

148745 - Investigation of Cracks in the Feed Pipe of Reactor in the Coal-to-Oil Hydrogenation Unit 

Pipeline transportation is one of the five major transportation industries, alongside railways, highways, water transportation, and aviation. Pressure pipelines, as special pressure equipment, are increasingly used in industries such as petroleum, petrochemicals, chemicals, electricity, urban gas, and heating engineering. They often operate in harsh environments with high temperatures, high pressures, and corrosive media. In recent years, with the development of industrial production towards large-scale and clustered operations, the number of pressure pipelines has increased sharply, and their operating parameters have become higher. The conditions of the pipelines and their surrounding environments have become increasingly complex, with various risk factors constantly intertwining and accumulating. Once a pressure pipeline failure occurs, it will have catastrophic consequences, especially when the pipeline medium is toxic, flammable, or explosive. The impact range may reach several hundred meters, leading to casualties and significant economic losses.

This paper takes the crack defects found in the feed pipeline of a hydrogenation reactor in the refining industry as an example. Through methods such as macroscopic inspection, composition analysis, hardness testing, metallographic examination, and EDS, the failure mode and mechanism were thoroughly investigated. Macroscopically, there are approximately 12 cracks, with lengths ranging from 10 to 20 mm, propagating from the outer surface inward, but not penetrating the pipe wall. Analytical results show that the material composition, hardness, mechanical properties, and metallographic structure all meet standard requirements, with no signs of material degradation. Subsequently, scanning electron microscopy was used to analyze the corrosion products at the crack tips, revealing a high content of chlorine elements. It is inferred that the cracks on the parent material of the pipe are due to chloride-induced stress corrosion cracking, where the cracks initiate from pits on the external surface of the pipeline and propagate inward and axially under the stress corrosion induced by chlorides. Through a thorough investigation of the operation and inspection records of the pipeline, it was found that the pipeline was constructed in 2009 and underwent multiple major maintenance inspections in 2012, 2015, and 2019, during which no recordable defects were found. However, this is the first time that PT testing has been conducted on this elbow and the adjacent straight pipes. Therefore, it can be speculated that the initiation and propagation of the crack occurred at the interface of the insulation aluminum sleeve or at the location of the damaged aluminum sleeve, where water ingress is likely, leading to the concentration of chloride ions from the atmosphere and insulation material at the pits on the surface of the pipeline.

 Finally, the paper proposes corresponding suggestions for subsequent management, emphasizing the need to control the surface quality of pipelines to avoid deep pits and to inspect and repair the pipeline's insulation aluminum jacket to prevent rainwater infiltration and regularly anti-corrosion paint even for stainless steel.

Presenting Author: Xufeng Li Guangdong Institute of Special Equipment Inspection and Research

Presenting Author Biography: Special equipment inspection, safety assessment

Authors:

Xufeng Li Guangdong Institute of Special Equipment Inspection and Research
Shengzi Lu Guangdong Institute of Special Equipment Inspection and Research
Weijian Luo Guangdong Institute of Special Equipment Inspection and Research