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Corrosion Sl Part Three
- 3. Processes and packages are made out of many different types of materials of construction Depicted here pumps, valves and tanks to show variables that add complexity All at different corrosion potentials Raw Materials Final Products
- 13. Equipment Design
- 15. Enough distance for coating Not Desirable DESIRABLE Weld not accessible for grinding Not enough distance for coating No radius Weld accessible Radius Design Considerations
- 16. Steel P i t (anode) Alloy (cathode) Protective coating Joining Dissimilar Metals Coating holiday-undesirable
- 17. Skip weld Welding Considerations SKIP WELDS Crevice-undesirable
- 18. Special attention required Desirable Continuous weld Skip weld Welding Considerations
- 19. Flush Rough Smooth Smooth contour (as-welded or ground) for coating Undercut Rollover Porosity Welding Considerations Good Undesirable
- 20. Corrosion source Threaded parts Round corners Sharp corner Inside of vessel Desirable Flange outlets Weld Inside of vessel 2” Min. Higher Energy state
- 21. Grind smooth Undesirable Desirable Continuous fillet weld Gap Weld Inside of vessel Gap Crevice Crevice
- 22. Crevices AVOID AVOID BETTER PREFERRED Joining Details
- 40. Formulating to Avoid Corrosion Tendencies
- 49. Fiberglass Material Glass Resin NA
- 50. FRP Attack Delamination Resin dissolved
- 58. Coating Testing for Continuity Checking for pinholes in the coating that would be sites for corrosion to occur
- 59. MEIR Database
- 62. Inhibitors Cathodic protection Coatings and Linings Materials Selection and Design NACE Technical Committees NACE “International Corrosion Society” Water NACE International
Hinweis der Redaktion
- There are several options to consider when combating corrosion issues. A familiarity of the options is useful to be able to select the right course of action to avoid a particular form of corrosion. Areas in Colgate where there have been issues with corrosion are displayed for discussion. MEIR stands for Materials of Engineering Information Requests. The database is a record of department testing, materials of construction recommendations, and plant surveys. There is a methodology for materials engineering selection. This is discussed in some detail and backed up with a handout. Having a question and not having anyone to answer can be very frustrating and not only that, not addressing it could lead to a serious issue later on. It is better to consult with experts to determine the right answer and direction. A large number of consulting contacts are included in the handout. The “specialist” recommendations for Colgate to avoid issues due to corrosion.
- Operating Conditions- Precise definition of the chemical environment, including the presence of trace compounds is vital. Conditions to be defined include, temperature, pressures, flow rates, liquids vs. gaseous phases, aqueous vs. anhydrous phases, continuous vs. intermittent operation. Abnormal or upset conditions should also be defined. Review of Design- the most important consideration are the welds. Will they have adequate corrosion resistance. Other items to consider are the welds should be free of surface defects, such as porosity, slag inclusions, incomplete penetration, or lack of fusion. Low carbon stainless steel needs to be considered. Consideration of materials of construction , first base it on reliable past experience. The list of materials to choose from is large and getting larger all the time. Exclusions examples, pressure to high for FRP, temperature to high for plastics, or environment to aggressive for carbons steel, chlorides and pH for 304 or 316 SS. Other areas to consult are literature surveys or an in-house materials expert. Evaluation of materials- the keys for this to happen are 1) Degree of uncertainty after available information has been considered, 2) The consequences of making a less than optimum selection. 3) The time available for evaluation. Follow-UP Monitoring- once built installed and commissioned the process should be monitored by the materials engineering expert to confirm the selection of materials of construction as adequate. Changeovers and shutdown times are generally good times for inspection.
- This conceptually shows that our processes are made of various types of parts with different shapes, geometries and materials of construction. When these parts are subjected to various chemistries, our products, the parts can become reactive. Why because they are at different potential energies based on their shapes, geometries and materials of construction.
- Operating conditions is the most important piece of information that you can convey to a corrosion/materials engineer. With all of the information given a corrosion engineer can give the process engineer the forecast on what sort of corrosion issues you need to avoid.
- The more complex a process is from a component point of view the more critical it is to make sure it is designed properly and out of the correct materials of construction.
- The most valuable information for a engineer is similar case histories. Corrosion is very difficult to predict exactly and it is always best to look at other real life data first.
- It cannot be overstated.. Corrosion testing is very important when you do not have data to base a materials of construction decision on. As we have seen, 316L SS is often times not the right answer.
- There are so many different types of corrosion tests that it is best to consult someone with experience in corrosion testing. You can very easily be mislead by a corrosion test if it is not conducted in the right way to simulate the real life conditions.
- Welded U-bends are an excellent way to study stress corrosion cracking possibilities. In addition data on pitting and crevice corrosion is obtained at the same time. Crevice corrosion where the teflon bushings touch the metal.
- There is a lot of corrosion information on 304 SS as it is the most common engineering material out there. This shows the effect again of salt and pH on it.
- The design of a structure is frequently as important as the choice of materials of construction. Design should consider mechanical and strength requirements together with an allowance for corrosion. In all cases, the mechanical design of a component should be based on the materials of construction. This is important to recognize , since materials of construction used for corrosion resistance vary widely in their mechanical characteristics.
- The most general rule for design is avoid heterogeneity. Dissimilar metals, vapor spaces, uneven heat and stress distributions, and other differences between points in the system lead to corrosion damage. Hence, in design, attempt to make all conditions as uniform as possible throughout the system.
- Self explanatory.
- Sometimes a design requires different metals and a coating to protect them from corrosion. In that case make sure you have coating that is thick enough to avoid pinholes where the environment could prematurely fail the anode of the two metals.
- Skip welding leads to crevice corrosion and should be avoided.
- Self explanatory
- This slides shows the issue of not using ground welds. Rough surfaces lead to corrosion.
- This slides points out that sharp corners and threaded parts lead to corrosion issues. Threaded parts are crevices and sharp corners are at higher stress.
- The point here is that seamless tube can have defects. Secondly that welded tube heat exchangers should be leak testes at a higher pressure than the working pressure.
- This is a general slide and that is should be mentioned that velocity of fluids can various effect on engineering materials. There are cases where increased velocity can slow down corrosion processes.
- The first refers to heat treatment of steels. There are several different types of heat treatment depending on the alloy and the results you are trying to achieve. The basic idea is to relieve locked in stresses from fabrication and to homogenize the chemistry in welds for example. Mechanical refers to forces used to dimple the surface to relieve surface stresses.
- By knowing the expected general corrosion rate and the anticipated plant life, the designer can calculate the extra wall thickness required for corrosion resistance of the process equipment he is designing.
- It is necessary for reliable plant operation that process equipment be inspected on a regular basis in an effort to anticipate failures and prevent unscheduled shutdowns. Some plant operations schedule an annual shutdown or turnaround at which time it is convenient to inspect suspect equipment.
- As shown in the beginning of the course, we have had failures of 316 SS. We need to be more prudent in the future, to examine our processes and equipment for corrosion issues.
- Elevated temperatures above 140 F , stress corrosion cracking is a threat. Strong acid such as sulfuric, and hydrochloric. Strong bases such as NaOH. Salt causes pitting corrosion. Abrasives cause erosion. High flow rates cause erosion.
- Tanks, Piping, Mixers, Heat Exchangers, Valves- Looking for general, pitting, or stress corrosion cracking Moving Parts- Looking for wear Crevices- Sites for crevice corrosion to occur. A good example would be tank pads. Heterogeneity- Look for galvanic corrosion issues Pressure and Vacuum leave equipment more sensitive to corrosion issues .
- Water piping because it could be a source of contamination. Steam and Utility piping because of possible erosion corrosion and the importance of it to the running of the plant Underground lines because of the threat to the environment.