Corrosion Sl Part Three
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  • 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.

Corrosion Sl Part Three Corrosion Sl Part Three Presentation Transcript

  • Module 3 “Engineering Considerations”
    • Materials Selection and Testing
    • Equipment Design
    • Inspection for Corrosion- Process Check Points
    • Formulating to Avoid Corrosion Tendencies
    • Engineering Materials- Critical Points
    • Database Resources
    • Review
  • Materials Selection Process
    • Depends on Operating Conditions
    • Review of Process Components
    • Consideration of Materials
    • Evaluation of Materials
    • Follow-Up Monitoring
  • 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
  • Operating Conditions
    • The chemical environment should be defined precisely, including the presence of trace compounds.
    • Temperatures, pressures, flow rates, liquid vs. gas, aqueous vs. non-aqueous, continuous vs. intermittent operation, media used for heating or cooling, and product purity requirements.
    • Abnormal or upset conditions.
    • pH range and salt levels
  • Review Process Components
    • Size
    • Complexity
    • Criticality in service
    • - For example: Consider critical , unique pieces of equipment in a single train continuous process, where one component failure would shutdown the entire operation. Rotary valve- Oral Care, Soap Column-Continuous Soap making.
  • Selection of Materials of Construction
    • Pertinent past experience
    • Making a list of materials to choose from and their properties
    • Vendors ( we rely to heavily on them)
    • Literature survey
    • MEIR database
  • Testing of Materials
    • Corrosion testing is needed when:
    • There is uncertainty about the right material to use
    • Significant consequences if the wrong material of construction is used.
    • - Consequences- Product contamination or recall, liability, safety.
  • Objectives of Laboratory Corrosion Testing
    • Predict service life
    • Determine the suitability of a engineering material for a given application
    • To rank new engineering materials
  • General Corrosion Testing Guideline
    • Use a testing procedure that fits the situation, consult if necessary.
    • Observe samples carefully before and after testing
    • Take pictures before and after for comparison
    • Simulate the service environment as closely as possible
    • Effects to take into account; trace impurities, suspended solids, aeration, temperature and pH.
    • Corrosion samples can be ordered from Metal Samples in Munford, Alabama http://www.alspi.com/ms.htm
  • Corrosion Testing Example
    • U Bend testing to determine the relative stress corrosion cracking resistance of 304L, 316L and 2205 alloys
  • Lab Data pH and Chloride effects on 304 SS
    • pH 2 pitting at 0.1 % CL at 25 C, cracking at 60 C
    • pH 7 pitting at 0.1 % CL at 60 C, cracking at 80 C
    • pH 12 no pitting at B.P., cracking at 1% CL at B.P.
    • Test duration approximately 1 year
  • Handout on Material Selection
    • See section on “Materials Selection” which has an in depth discussion on this subject
    • Pages 321-325
  • Equipment Design
    • Use proper welding techniques - problems with stainless, eg., heat affected zone (HAZ); therefore use stabilized grades “L” or Titanium stabilized in Europe.
    • Select the right weld filler materials for the project
    • Use of dissimilar metals should be avoided
    • “ Mechanical” design at lower stresses
    • Underground structures need corrosion protection
    General
  • Enough distance for coating Not Desirable DESIRABLE Weld not accessible for grinding Not enough distance for coating No radius Weld accessible Radius Design Considerations
  • Steel P i t (anode) Alloy (cathode) Protective coating Joining Dissimilar Metals Coating holiday-undesirable
  • Skip weld Welding Considerations SKIP WELDS Crevice-undesirable
  • Special attention required Desirable Continuous weld Skip weld Welding Considerations
  • Flush Rough Smooth Smooth contour (as-welded or ground) for coating Undercut Rollover Porosity Welding Considerations Good Undesirable
  • Corrosion source Threaded parts Round corners Sharp corner Inside of vessel Desirable Flange outlets Weld Inside of vessel 2” Min. Higher Energy state
  • Grind smooth Undesirable Desirable Continuous fillet weld Gap Weld Inside of vessel Gap Crevice Crevice
  • Crevices AVOID AVOID BETTER PREFERRED Joining Details
  • Crevices and Drainage
    • Flanges, threaded connections, drain lines should be avoided. Invitation to pitting by oxygen concentration cells.
    • Heat exchanger crevices are highly susceptible to attack
    • Low legs in piping are to be avoided as they may retain water
  • Heat Exchanger Tubing
    • Seamless tube- What to watch out for-
    • Extrusion tears, Lap defects (stringers)
    • Welded tube- Pinholes: test at 150 % of the highest working pressure
  • Velocity Corrosion Control
    • Piping high end velocity 1.2 to 1.8 m/sec (4-6 ft/sec)
    • Tubing/heat exchangers up to 8 m/sec (25ft/sec)
    • Orifice plates, throttling valves, pump impellers – erosion resistant materials are needed
  • Stress Relief
    • Two types
      • Thermal
      • Mechanical
  • Thermal
    • Through heat treatment of stainless steel we can lower residual stresses and therefore the risk to stress corrosion cracking.
    • Typical temperatures are above 1000 F or 600 C ( Heat Treat Furnace )
    • Possible application would be welded mixer blades.
  • Mechanical
    • Consists of shot peening the surface of an item or equipment with an appropriate type of shot
    • Surface in compression is more resistant to mechanical fatigue, corrosion fatigue and environmental cracking.
    • Applications – shafts and blades etc.
  • Corrosion Allowance
    • Use for general corrosion situations, i.e.. Mainly carbon steel
    • The idea is to leave the required thickness for piping or vessels that will meet the mechanical design requirements of temperature and pressure over the estimated useful life.
    • This approach is practical for allowances of 3 to 6 mm or (0.13 to 0.25 in. )
  • Corrosion Inspection
  • Survey Plant sites for materials of construction issues
    • Why
      • To avoid possible product quality issues
      • To avoid plant process failures ..
      • Process failures lead to safety, environmental and liability issues
  • Key Operational Checkpoints
    • Elevated temperatures above 140F ( 60 C)
    • Raw Materials (acids and base)
    • Anywhere your using salt (NaCl)
    • Anywhere your using abrasives
    • High flow rates ( > 1.2 M/sec velocity)
  • Key equipment Checkpoints
    • Tanks, Piping , Mixers, Heat Exchangers, Valves
    • Moving Parts such as in Fillers
    • Crevices
    • Heterogeneity- more than one material of construction.
    • Equipment operating under pressure or vacuum
  • Other Critical Inspection Points
    • On-Site water piping
    • Steam and Utility piping
    • Underground lines or piping
  • Plant Inspection Tools
    • Visual Observation
    • Ultrasonics- Tanks- General corrosion
    • Magnetic Particle- Welds and stress corrosion
    • Depth Gauge- localized corrosion, pitting
    • X-rays – Tank and equipment replacement decisions
    • Boroscope- Optical fiber microscope for determining corrosion severity in hard to reach places such as tubes in a heat exchanger
  • See Handout on Inspection and Failure Analysis
    • Chapter 38 Inspection and Failure Analysis
    • Inspection techniques see pp. 290-292
  • Ultrasonic Thickness Testing
    • Determining the wall thickness of storage tanks tells us the margin of safety and the degree of risk from an environmental spill.
  • Close-Up Inspection
    • Of plant machinery and processing equipment is a way of determining if any corrosion is occurring.
    • This is especially important on stainless steel parts.
    • Early signs pitting or cracking could be a serious business issue.
  • Manufacturing Corrosion Exercise
    • Your given the added responsibility of making sure your plant does not incur any significant corrosion issues that could impact manufacturing downtime, EOHS, or product quality.
    • Givens:
    • Your plant uses NaCl to make Softsoap products. Your plant also makes Toothpowder using 440 stainless rotary valves, Soap/Lyes, Glycerin, Detergents Liquids and Powder.
    • Based on Module 1, Module 2, and what you learned so far in Module 3, What areas in the plant would you check for corrosion and how?
    • Hints- Use the examples given, the inspection checklist and tools, and the section handout on “Inspection and Failure Analysis.”
  • Formulating to Avoid Corrosion Tendencies
  • Salt Concentration NaCl
    • Sodium chloride is the worst possible component from a corrosion standpoint in a formula.
    • Minimizing it is important, less than 1% would help to prolong stainless steel equipment life and help minimize micro issues.
  • pH (Acidity/Alkalinity) values
    • pH extremes are bad for engineering materials.
    • Corrosion potential goes up significantly below a pH of 5.5 and above 9.
    • There are of course exceptions to this guideline, for example under erosion conditions high pHs are generally better.
  • Formula Corrosion Inhibitors
    • Sodium nitrate ( for Cl- ) pitting
    • Sodium silicate ( general corrosion)
    • Sodium sulfate ( for Cl-) pitting
    • Concentration and type to use depends on the circumstances.
    • Engineering Materials- Critical Points
  • Metal Behavior
    • Different metals corrode differently due to there metallurgy
    • - Metallurgy: Science of making metals from raw materials
    • Some effects
      • Carbon Steel (general corrosion)
      • Gray cast iron (graphitization)
      • Ductile iron (usually pitting, some graphitization)
    • Stainless steel
      • Passivity due to oxide film
      • Susceptible to corrosion in various environments
      • Need to select the proper stainless for the environment
  • Types of Stainless Steels
    • Martensitic
      • 12% – 17% Cr
      • minor other elements
      • moderate corrosion resistance in mild environments, heat treatable
    • Ferritic
      • higher Cr composition than Martensitic (12% – 30%)
      • better corrosion resistance to high temperatures
  • Stainless Steels (cont)
    • Austenitic
      • Cr: 17% – 25%
      • Ni: 9% – 10%
      • generally more corrosion resistant than martensitic (304/316)
    • Duplex alloys (2205/2507)
      • mixture of ferritic and austenitic
      • increased strength and corrosion resistance, for stress cracking environments
  • Non Metallic Issues
    • Concrete
      • Freeze thaw cycle- leads to cracking
      • Rebar corrosion
      • Attack by de-icing salts and acids
      • Hydrogen sulfide attack in sewers
    • Plastics
      • UV attack
      • Thermal stresses and cracking
      • Solvent attack Resins- FRP
  • Fiberglass Material Glass Resin NA
  • FRP Attack Delamination Resin dissolved
  • Composite (FRP) Tank Failure
    • Problem : Internal PVC liner weld failed mechanically.
    • Bleach then attacked inner FRP resin (non-compatible) glass support structure.
    • Could not see the damage to the outer liner.
    • Solution : Redesign tanks without liners.
  • FRP Impact Cracks
  • Coatings and Linings
    • Separate material from the environment
    • Provide good adhesion to the metal
    • Serve as primer for topcoats
    • Provide sacrificial protection to the metal
    • Resist abrasion, impact and soil stress
    • Hold an inhibitor at the metal surface
    • Resist water absorption
    Functions and qualities of coatings
  • Functions and Qualities of Coatings (cont)
    • Prevent contamination
    • Protect against high temperature oxidation
    • Be safe to use
    • Be environmentally acceptable
    • Provide good electrical insulation for underground structures
  • Coating Application Considerations
    • Surface preparation
    • Atmospheric conditions
    • Application techniques
    • Inspection
      • Wet and dry film thickness
      • Electrical (holiday) inspection
  • Surface Preparation-Blasting
  • Coating Testing for Continuity Checking for pinholes in the coating that would be sites for corrosion to occur
  • MEIR Database
  • MEIR’s
    • Materials of Engineering Information Requests
    • Historical information
    • Information also in hard copies and index.
    • Many chemicals are included
  • Resources
    • NACE International Corrosion Society- www.nace.org
    • ASM American Society of Metals- www.asminternational.org
    • ASTM American Society of Testing Materials- www.astm.org
    • ASME American Society of Mechanical Engineers- www.asme.org
  • Inhibitors Cathodic protection Coatings and Linings Materials Selection and Design NACE Technical Committees NACE “International Corrosion Society” Water NACE International
  • What did we learn?
    • A guideline for selecting materials of construction
    • There are different kinds of stainless alloys and the selection of the right one for the specific application is important
    • Metallic and non-metallic materials of construction have there Achilles heels.
    • Design with lowest stresses possible, eliminate corners, provide smooth welds, and finish
    • Key materials of selection points; high temperature, areas of wear, highly stress parts.
    • There is historical data on engineering materials ( MEIR’s)
    • Resources for corrosion information – such as NACE and ASM
    • A checklist for conducting Corrosion Audits.
  • — Remember —
    • Corrosion Engineering Doesn’t Cost —
    • It Pays!