Many of these DSS REACs have remained in service successfully, with some in service for more than 30 years. However, several incidences of cracking failures of both REACs and associated piping have occurred in industry. Some failures have resulted in major plant damage and long outage time. Some refiners have been replacing DSS REACs with Alloy 825 to avoid in-service cracking risk. Others have made risk assessments and continue to operate with DSS REACs, often with periodic in-service crack detection inspection.
Step 3 is to adjust the risk rank from step 2 based on in-service crack detection inspections and other testing. Data collected on time to failure, such as is shown in Figure 1, has shown the time to fail has been from a few hours after start-up to approximately 28 years in service. Successful long-term service does not demonstrate freedom from future cracking. However, risk rankings may be conservatively judged to be higher than actual due to uncertainty about fabrication quality and ferrite control. Multiple highly effective crack detection inspections help reduce uncertainty and can be used to lower assigned risk rankings. Conversely, evidence of in-service cracking would confirm that ferrite control was not good enough and result in an increase in assigned risk.
We are aware of at least two cases where 2205 DSS REACs failed during tightness testing with high pressure hydrogen during commissioning but before being put into service and before being exposed to sour water. Ruptures of the header boxes occurred in both cases with cracking of corner welds between top or bottom plates and tube sheets or plug sheets. Hydrogen tightness testing is done during commissioning with pressure increased to normal operating pressure over a period of several hours or days. In the two cases noted, header box ruptures occurred when the hydrogen tightness pressure exceeded 2000 psig, less than full expected operating pressure in both cases. Both header boxes had been hydrotested at pressures significantly higher than the pressure at failure. Weld defects probably contributed to both failures. Cracking initiated at a repair weld in one case.
DSS REACs that have passed the hydrogen tightness test and have been placed in service have demonstrated resistance to hydrogen environment embrittlement (HEE). HEE is, therefore, not considered when assessing cracking risk in operating REACs.
A three-step approach for assessing the risk of SSC in DSS REACs has been summarized. It requires consideration of the effectiveness of ferrite control during fabrication, operating environmental severity and in-service crack detection inspection results.
Due to the uncertainty with the performance of DSS in REACs and associated piping, existing DSS REACs are often being replaced with Alloy 825 to avoid in-service cracking risk. When alloy is needed, Alloy 825 is typically being specified for new REACs and piping rather than DSS.
Becht has been helping clients to assess the risk of cracking in their DSS REACs around the world. Dave Moore is considered an industry expert in refinery damage mechanisms, specifically as it relates to cracking in DSS REACs. In addition, the PONO Corrosion and Metallurgical experts can help your specialists with risk assessments of your DSS REACs.
A general overview of corroded sites for the grade 2202 wire after 541 days of exposure is shown in Fig. 9a in accordance with the X-ray CT in Fig. 2. The same regions scanned by X-ray CT were imaged in the scanning electron microscope (SEM), and a good correlation was obtained. SEM analyses revealed only a surface view of the corroded wire, and therefore, the volumetric information such as crack propagation towards the wire interior could not be correlated. However, information from the wire surface with nanometre spatial resolution was obtained and surface cracks not detected by X-ray CT could be imaged in the SEM. Both X-ray CT and SEM examinations revealed complementary information in assessing the extent of SCC.
The less common complications include choroidal neovascularization (CNV) formation . CNV formation after clear lens extraction was reported in all patients with preoperative macular lacquer cracks , but the presence of myopic CNV in the fellow eye was also a risk factor for the operated eye . There is no clear explanation as to why eyes undergoing RLE are more susceptible to early age-related macular degeneration (AMD) occurrence with or without CNV formation , but inflammatory mediators associated with biochemical environmental changes within the eye such as increased free radicals or growth factors can play important roles. 2b1af7f3a8