Everyone in the process industries understands the need to eliminate wasteful approaches and embrace environmental-related initiatives. Corrosion is one area where companies can demonstrate environmental improvements by using advanced materials for insulation, coatings and related processes. At the same time, an enhanced asset management strategy also reduces lifecycle costs.
Using a variety of inspection techniques such as thermography and radiography can be helpful in detecting corrosion.
The National Insulation Association provides some eye-opening estimates on the cost of CUI in North America:
- CUI causes the majority of piping leaks at about 65%.
- Small piping is a major risk; anything less than a four-inch diameter accounts for 81% of leaks
- The direct and indirect costs of CUI are quickly approaching one trillion dollars
Better surface prep
Abrasive blasting is often the first step in surface preparation for coating or insulation. The traditional manual approach requires a high volume of blast media including garnet, glass, steel or other metallic abrasives. The media must be contained, typically with a polymer-based barrier such as vinyl, captured and recycled and/or disposed of properly.
Robotic surface preparation, which works on horizontal and vertical surfaces, offers a more environmentally friendly alternative. It uses a fully contained HEPA-ready dust collection system and up to 100% recycled abrasive media. This significantly reduces landfill impact and costs, with up to a 90% reduction in blast media waste when compared to traditional abrasives. Instead of using 30 or 40 tons of media on a typical tank project, robotic surface preparation might generate less than one ton. Plus, it eliminates the need for vinyl barriers. Better productivity, schedule opportunities and reduced safety exposure are typical benefits.
Developing a CUI strategy
Likelihood of failure due to CUI is a constant issue with carbon steel assets, and the development of a comprehensive strategy is critical. In addition, a risk in one area often corresponds to negative consequences in other areas.
Populating a risk profile would involve a team with representatives from operations, management and environmental health and safety, as well as CUI experts. Next, a company, or a team with representatives from engineering, reliability, inspection and maintenance needs to identify at-risk assets and assess their condition. Assets most at risk include:
- Those in proximity to cooling tower mist, steam vents or deluge systems
- Areas subject to process spills, flue gas or acid vapors
- Protrusions extending from an insulated/jacketed system
- Systems that have skin temperatures from 119°F to 225°F
- Areas subject to ingress of moisture, such as those with damaged insulation
- Insulation near vibrating systems, which have potential to damage it
- Areas showing visible damage
- Steam tracing lines versus electric heat tracing
- Dead legs on insulated piping systems
- Elbows/fittings at low points of vertical piping runs
- Insulation support ring or stiffener ring areas on vessels
- Cyclical operating systems, such as ambient to warm, hot, warm, ambient and idle
The goal is to evaluate the likelihood of failure and produce a risk matrix with quantitative measures. An example is shown in the figure above, which was created as part of a reliability, availability and maintainability (RAM) assessment process.
Inspection programs
A CUI inspection strategy aligns the RAM classification of an asset with appropriate inspection technologies. Using a one to five scale, with one equaling low RAM and five equaling high RAM, inspection strategy (IS) examples include:
• IS 1 – Visual observation
• IS 2 – Qualitative NDE techniques for presence of water, etc.
• IS 3 – Spot strip of insulation, NDE techniques at suspect areas only
• IS 4 – Major strip of insulation up to 50% of area, special NDE techniques
• IS 5 – Complete strip and NDE techniques
A variety of NDE (non-destructive evaluation) methodologies exist. Balancing an inspection program with the RAM level brings peace of mind by mitigating risk through a planned, rather than reactionary, approach. Over time, this type of consistent approach drives down risk, increases environmental benefits and ultimately decreases cost of ownership.
CUI for RAM
The ultimate efficiency plan comes from reducing and/or eliminating waste at the source. In the case of CUI, that means longer periods between inspection and extended service life. Before going further, let’s go back to the beginning and consider the simplistic “corrosion cell” and its four essential components: an anode, a cathode, water — or more technically, an electrolyte to act as a conducting environment for ions — and an electrical connection from electrode flow from the anode to the cathode.
Often a risk in one area corresponds to negative consequences in others as shown in this Site Risk Matrix.
With unprotected mild steel, adding water or humidity completes the corrosion circuit. Adding a liquid coating breaks the circuit by acting as a barrier that prevents the electrolyte from completing the corrosion cell. A low VOC coating is an environmentally friendly option. However, the challenge is keeping the coating intact from mechanical damage, UV damage and chemical exposures. Inevitably, conventional liquid coatings begin to fail, and corrosion begins. Corrosion typically undercuts the coating; then blisters from the iron oxide extend the damage. Environmental factors, such as salts and chemicals, can accelerate the process. As a result, coatings last five to 15 years before base material needs abrasive blasting and coating reapplication.
Innovative approaches and materials
As mentioned previously, cost savings through the use of alternative approaches and materials offers substantial benefits over the cost of ownership of assets — from a direct cost, risk, environmental and total cost of ownership perspective. A few examples include:
- Metal coatings versus liquid coatings
- Non-rigid insulation systems to avoid costly mechanical damage
- Hydrophobic insulation systems that wick or hold water
- Inspection techniques to identify issues early and often to core or critical systems
Metallizing as a barrier
To extend service life and cost of ownership, consider metallizing — typically aluminum — as a barrier coating. Metallizing provides a superior barrier coating for many exposures, as well as a galvanic-effect benefit where the coating acts as a sacrificial anode. With an additional conventional barrier coating, there is the potential for synergy as the protection gained is greater than the sum of each system as a stand-alone application.
While metallizing is not new, it remains under-utilized. Though the initial costs are higher by 20-40%, thermal spray coatings lower cost per year by up to 50%. Those savings are not just a good business decision, they demonstrate good environmental stewardship. More simply stated, by doing more with less, process industries can improve their bottom line while furthering sustainability.
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