Monitoring of hydrogen embrittlement for hydrogenation processing plants

CATEGORY: HYDROGENATION
FM2008 - Evaluation, Inspection and Monitoring of Structural Integrity / 545-548
Monitoring of hydrogen embrittlement for hydrogenation processing plants
Zhengdong Wang *, Zhanya Xing, Kuilong Zhu, Fu-Zhen Xuan
zdwang@ecust.edu.cn
a MOEKey Lab. of Safety Science of Pressurized System, East China University of Science and Technology, Shanghai 200237, China
Abstract
A real time monitoring system is suggested in this paper to predict hydrogen embrittlement for the wall materials of hydrogenation reactor and pipeline in petrochemical plants. Mechanism of hydrogen embrittlement is discussed for both hydrogen-induced cracking in the reactor wall and hydrogen-induced disbonding under clad. A critical description of hydrogen induced cracking is introduced to set up a criterion for the embrittlement. An opposite derivation model is assumed to detect the hydrogen concentration in the wall according to the amount of hydrogen escaped from the outside wall with a technology of hydrogen sensor. Electrochemistry hydrogen penetration testing technique is utilized for determination of diffusion coefficient the material interested. The electrochemistry hydrogen sensor is designed for its feasibility of real- time monitoring and assessment of hydrogen embrittlement for the equipment. It is pursued by the research to make a more impersonal judgment of safety of the hydrogenation reactor with real time tracing of operation. A remote inspection system is designed based on computer network technology to monitor the plant subjected to hydrogen attack. To make sure of hydrogenation processing plant safely for a long period of operation, it is necessary to scheme precautionary maintenance plan and improve working condition to prolong its life in service.
Introduction
Hydrogenation processing technology has been applied widely in modern petrochemical industry. The hydrogenation processing plants are mostly subjected to high pressure, high temperature and environment of corrosion. The main problems for the equipment are usually the hydrogen embrittlement, hydrogen-induced cracking of the wall materials and hydrogen-induced disbonding of stainless steel weld overlay. During a long period of operation at hydrogenation processing temperatures，irreversible temper embrittlement in materials is thought to be due to precipitation of carbides in the form of films at grain boundaries.
However, the hydrogen-induced cracking may not happen at normal operation, but may occur during the process of shutdown or emergency cooling operation. Steels exposed to hydrogen environment absorb atomic hydrogen at high pressure and high temperature. When the reactor is cooling, the solubility of hydrogen in steels becomes lower and the local hydrogen concentration on matrix-inclusions interfaces or weld fusion line may build a condition for cracking to occur.
Research on hydrogen embrittlement of the materials has been carried out in the following fields in the past 2 decades [1-6]: (a) Mechanism of hydrogen-induced cracking in reactor steels and disbonding in stainless steel weld overlays; (b) Evaluation of the hydrogen embrittlement susceptibility in reactor steels; (c) Hydrogen charging technique for hydrogen-induced cracking test; (d) Finite element analysis of hydrogen diffusion and cracking process; (e) Simulation procedures for prediction of hydrogen induced embrittlement in hydrogenation pressure vessels; (f) Life extension for hydrogenation reactors with safety operation.
However, it is very difficult to make a more impersonal judgment of safety of the hydrogenation plant with real time tracing of operation. In this paper, a monitoring system is suggested to predict hydrogen embrittlement for the wall materials and an electrochemistry hydrogen sensor or probe is designed for its feasibility of real-time monitoring and assessment of hydrogen embrittlement for the equipment. 
Free Full Text Source: http://chemech.ecust.edu.cn/papers/FM2008-WangZD-1.pdf