Stress Corrosion Cracking In Acid Research Articles

The Study on Degradation of Stainless Steel Clad Plate Used for a Shift Reactor in Coal Chemical Plant

Shift reactors are widely used in the petroleum and chemical industries, and especially in the coal chemical plants. The degradation of the reactor is critical to the safe operation of coal chemical plant. In this paper, a shift reactor after 8 year service was chosen. The test block taken from the reactor cylinder with the stainless steel clad plate was used and the test samples from the test block were prepared. And then, chemical composition analysis, metallographic examination, tensile and hardness tests were performed. The scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) method were used to study the degradation and degradation mechanism of the reactor. The metallographic analysis results show that there were a large number of carbides segregated in the grain boundary and the intergranular cracks were observed for the samples in the weld zone of the stainless steel clad plate. The SEM and EDS results indicate that the corrosion medium (i.e. polythionic acid) was found in the fracture surface of the samples from the weld zone of the stainless steel clad plate. The XRD test results show that the tensile residual stress occurred for the welding of the stainless steel clad plates. It is found that the degradation mechanism of the shift reactor was due to the polythionic acid stress corrosion cracking.

Alloy for resistance to polythionic acid stress corrosion cracking for hydroprocessing applications

In certain process units, such as hydrocracking, soda ash washing (neutralization) of austenitic stainless steel is required during turnarounds to mitigate the potential for polythionic acid stress corrosion cracking (PTA SCC). Soda ash washing can be a costly and time consuming endeavor for the refiner. This paper introduces a grade of austenitic stainless steel, a proprietary version of Type 347LN, that does not sensitize with long-term exposure to elevated temperature, thus rendering it immune to PTA SCC. ASTM A262 Practice A corrosion test results will be presented for samples isothermally aged at 565°C for a duration of up to 10,000h. These data will be compared to samples of conventional Type 347, Type 321, and Type 304H similarly aged. Photomicrographs will be shown that demonstrate the lack of grain boundary sensitization, and also the lack of grain boundary ditching in the oxalic acid test. Replica analysis of a heater tube from commercial service at 460°C average tube wall temperature for 12years showing no evidence of sensitization or grain boundary precipitation will also be presented.

Cracking investigation of a pressure transmitter tapping line

This article describes the findings of an investigation on cracking of ethylene furnace pressure transmitter tapping lines made of stainless steel type 304H. A detailed failure analysis using several characterisation techniques such as visual and metallographic examinations, SEM/EDX, XRF/C&S as well as finite element analysis uncovered that the cracking was caused by polythionic acid stress corrosion cracking that took place due to presence of condensate, sulphides and oxygen in contact with sensitised material. Several corrective measures to prevent similar failures are discussed.

Failure of hydrocracker heat exchanger tubes in an oil refinery by polythionic acid-stress corrosion cracking

Heat exchanger tubes of a hydrocracker unit in an oil refinery developed cracks at the bent sections after about 48 h of operation at 400 °C following a period of downtime. The tubes were fabricated from 321 stainless steel. Detailed analysis by various electron-optical techniques and X-ray diffraction showed that the tubes were cracked by stress corrosion cracking induced by polythionic acid. Due to the presence of H 2S in the environment, the inner surface of the tubes was converted into sulfur-bearing scale during operation. This could promote the formation of polythionic acid by aqueous condensates during downtime leading to cracking in the presence of residual internal stresses.

An acoustic emission study of stress corrosion in a chopped strand mat gfrp composite

Acoustic emission ( ae) is used to detect stress corrosion damage as it occurs in an E-glass chopped strand mat-reinforced polyester resin. AE activity is observed when samples under tension, having exposed cut edges, are subjected to an environment of either sulphuric acid, which mainly corrodes the fibres, or acetone which degrades the resin. In water there is negligible ae, showing that the acid corrosion ae originates from chemical attack, rather than merely physical penetration of aqueous solution. Linear location of ae signals proves to be an efficient means of determining the onset of stress corrosion cracking in acid, while the ae amplitude distribution is also useful in this respect. In monitoring the growth of stress corrosion cracks in this material in acid it is found that the ae event rate varies with applied stress according to a power law, and there is an approximately linear relationship between the residual strength of the samples and the cumulative total of detected ae events.

安定化ステンレス鋼溶接部の長時間時効によるポリチオン酸応力腐食割れ感受性の推定

The susceptibility to polythionic acid stress corrosion cracking of stabilized austenitic stainless steel weldments was investigated as a function of their sensitization measured by EPR method. The results showed that type 321 and 347 stainless steels became susceptible to stress corrosion cracking when the sensitization index in EPR test exceeded the value of 10%.In order to prevent the stress corrosion cracking of the weldment throughout the long time service of 105 hours or more, some countermeasures such as a stabilizing heat treatment should be provided to the type 321 and 347 weldments when they are used over 480°C and 430°C, respectively.

Chemical studies of polythionic acid stress-corrosion cracking

Low temperature stress corrosion cracking of sensitized stainless steel, promoted by aqueous solutions of polythionates S xO 6 2−, and related sulfur compounds, particularly thiosulfates, has been a long known problem in the petroleum industry and more recently has cropped up in the nuclear power industry. Membrane permeation results presented here show that S 4O 6 2− and S 2O 3 2− do not function simply as sources of sulfide to promote hydrogen permeation and embrittlement. They do promote anodic dissolution, also generating an unusual adsorption-related anodic spike in voltammetric scans. The oxidation of iron sulfide scales, said to be the source of the substances in petroleum refineries, has been shown to give rise mostly to Fe 2O 3 and elemental sulfur, with low yields of both S 4O 6 2− and S 2O 3 2−.