staff | resumes | affiliated companies | recent projects/awards | insurance coverage | FAQs | Glossary | contact CEI
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
| sitemap |
Caustic Stress Corrosion Cracking Analysis
Summary & Discussion | Wetted Parts | Pools/Tanks Containing Alkali Metal | CEI Experience | Notes
Wetted Parts
The situation with wetted parts is that it is impossible to predict exact conditions during the reaction of residual amounts of alkalimetal with water vapor at all points in a pipe, reactor, or other component. With a SHS-processing method, local temperatures at the site of the NaK can and will exceed the lower limit of concern for caustic stress corrosion cracking (CSCC). Caustic concentration at any point will vary from anhydrous, at initial reaction with steam, to near zero when water-flushing. It is essentially impossible to predict the range of conditions that will exist at the point where a droplet of metal might be in contact with stainless steel. Factors such as the amount of metal in a location, the initial temperature of the base metal, location of high-stress areas such as welds, the dilution rate of the caustic, and the time at the temperature of concern cannot be predicted with accuracy. With NaK wetted parts, the large amount of water vapor introduced means the reaction at any one point will be rapid and hot but very short-lived. Within minutes after reaction begins on a wetted part, the reaction will be complete, the area will begin to cool, and the caustic will begin to hydrate.
By preheating the piping to 200°C, the base metal is above the temperature at which CSCC can occur, so the concern is the time at temperatures between approximately 120–180°C while the caustic concentration is between 30 and 70% by weight, in areas where the stress is above a threshold value for a sufficient time for CSCC to occur. In CEI’s experience, the correct combination of conditions would be present for only a very short time, if at all. The temperature window is likely to exist for a time period of less than one hour, which is essentially too short a time span for CSCC to occur, even at stress levels at the yield point of the metal.
CEI’s process for cleaning the alkalimetal wetted parts does not add stresses, because the process is carried out at atmospheric pressure. Localized stresses, particularly in welds, may be above the stress level required for CSCC. Even if this is the case, with general stress levels that are low, the most likely event would be a small crack and a leak, not a catastrophic failure.
CEI does not believe CSCC is a factor of concern in the cleaning of alkalimetal wetted parts.
Alkali Metal Consultants | Plant Automation | Chemical Manufacturer | Sodium Dispersions | Alkali Metals Disposal | Pollution Consultant | Etchant | Electromagnetic Pump & Flow Meters | Plant Designers | Pilot Plants | Process Engineering Consulting | Process Engineer | Project Management Engineers | Skid Mounted Pumping Systems
Creative Engineers Inc.
P.O. Box 206 | Phoenix, Maryland 21131
phone 443-807-1202 | fax 410-683-9707
info@CreativeEngineers.com