Session: 15-01-02: General Topics on Risk, Safety, and Reliability II

Paper Number: 164591

Cause Analysis of Crack in the Circumferential Weld on the Inner Wall of Hydrogen Evaporator 

In the petrochemical industry, the safety of pressurized special equipment is critical. Due to the influence of medium, temperature, pressure, and external environment, pressurized special equipment may suffer from corrosion thinning, environmental cracking, material deterioration (e.g. creep, low-temperature brittle fracture), mechanical damage (abrasion, scouring), and other problems. These damages are usually accumulated gradually during the operation of the equipment. Therefore, regular inspection is necessary to ensure its safe operation.
The characteristics of the pressurized special equipment determine that it may lead to serious consequences in the event of a problem, high temperature, high-pressure operating environment, and the presence of flammable, toxic media once an accident occurs, may cause personal injury and economic loss is immeasurable. 
This paper takes the periodic inspection of octenal gas-phase hydrogenation evaporator in the butanol plant of a large petrochemical enterprise as a case study, and finds two cracks with lengths of 3000mm and 2800mm in the circumferential weld of its inner wall. To investigate the causes of cracks, background investigation, magnetic particle inspection, ultrasonic inspection, crack profiling, hardness testing, metallographic inspection, and residual stress detection were carried out, and treatment suggestions were given in combination with its risk level. It is hoped that the results of this research can provide a reference for the regular inspection and defect treatment of similar equipment, thus promoting the safety management level of special equipment in the petrochemical industry.
After a comprehensive analysis, the cracks are considered to be thermal cracks produced in the manufacturing process; the cracks may be caused by high residual stresses due to excessive welding current; at the same time, relevant treatment suggestions are given for the defect treatment, which provides an important reference for future similar inspections.
The following recommendations are made for the subsequent treatment of equipment defects:
•    Eliminate cracks by grinding. If the depth of the crater formed by grinding is within 2mm, it is only necessary to carry out a smooth transition around the pit to prevent stress concentration.
•    If the crater formed after grinding exceeds 2mm, it should be patch welded and stress relief heat treatment If the crater formed after grinding is more than 2mm, supplementary welding and stress relief heat treatment should be carried out; in the heat treatment process, its temperature and holding time should be checked with emphasis.
•    In the manufacturing process of the same kind of pressure equipment, the inspection of the conformity between the welding parameters and the welding operation instructions should be strengthened; the proportion of non-destructive inspection of the surface can be increased after the welding operation is completed.
 

Presenting Author: Cong Deng Guangdong Institute of Special Equipment Inspection and Research

Presenting Author Biography: Special equipment testing and safety assessment

Authors:

Cong Deng Guangdong Institute of Special Equipment Inspection and Research
Jin Guo Guangdong Institute of Special Equipment Inspection and Research
Weijian Luo Guangdong Institute of Special Equipment Inspection and Research
Xufeng Li Guangdong Institute of Special Equipment Inspection and Research
Jiayue Liu Guangdong Institute of Special Equipment Inspection and Research
Junhui Zheng Guangdong Institute of Special Equipment Inspection and Research
Wufei Yuan Guangdong Institute of Special Equipment Inspection and Research
Huasheng Hu Guangdong Institute of Special Equipment Inspection and Research