Corrosion and Erosion Protection of Heat Exchanger Components On-Site with a Metal Alloy Upgrade Coatings
We protect Heat Exchanger components from aggressive erosion, corrosion, and metal wastage by upgrading the surface metal alloy in-situ, on-site, using IGS high velocity thermal spray (HVTS) coating solutions. The installation of IGS HVTS claddings as an erosion/corrosion mitigation strategy reduces the future maintenance costs, repair requirements, and downtime of heat exchangers operating with aggressive chemicals or flow parameters. Our proprietary coating technology is paired with the unmatched site experience of IGS to execute projects to strict quality standards in tight time schedules on shutdown / turnaround critical paths. We spray metal alloy coatings in the USA, Europe, Middle East, India, and other parts of the world.
Heat Exchangers in the Refinery and Petrochemical Processes
Wherever there is a requirement to transfer energy from one production stream to another (whether it is from a liquid, vapor, or gas), to raise or lower the process fluid temperature, a of heat rxchanger will be used. There are many designs of heat exchangers, and the equipment has many names in a refinery or petrochemical plant (phase change units, reboilers and condensers, waste heat recovery units, hot gas boilers, etc.). The most common types are shell and tube heat exchangers, where within the shell section, multiple tubes pass through, enabling the transfer of heat from the shell side fluids to the tube side fluids.
Dependent upon the design and operating parameters of heat recovery units and boilers, many corrosion challenges can occur. Typically, erosion/corrosion is common on the tube sheet surface. This can be due to a number of factors:
- Bimetallic (Galvanic) corrosion, the tube sheet, and tubes are made from different metals as they require different properties. This means that a bimetallic corrosion process can set up where these two metals are in contact and the right environmental conditions exist (g., anode, cathode, metallic pathway, and electrolyte). The tube alloy is typically more noble and more corrosion resistant than the alloy used for the shell or tube sheet.
- The tube sheet needs to be strong enough to hold the tube bundle (typically steel)
- The tubes need a high heat transfer efficiency to allow energy to flow from one fluid to the other (typically a copper-based alloy)
- Erosion/Corrosion at the mouth of the entrance to the tubes. In many high-temperature gas exchangers, the high velocity combined with the operating conditions leads to metal dusting corrosion on the leading edges of the tubes.
- Corrosion in dead areas of the heat exchangers or when offline. Condensation can occur when reboilers are offline or not operated in their designed temperature range, this can lead to the leaching of corrosive media from the gas flow (g., H2S or CO2 in sour gas) and aggressive corrosion on the exposed metal.
- Unanticipated operating conditions. The design conditions for a process are frequently not met in terms of the operating environment or the chemical composition, meaning that the alloy of choice for the equipment is no longer fit for purpose as the environment has changed from the original FEED. This can be due to the carryover of corrosive media (g., H2S, CO2, acids from high TAN crude, amine, etc.), process control, etc. leading to corrosion of the tube sheet, header box, end covers, and shell.
Integrity Limiting Corrosion of Heat Exchangers
When these corrosive or erosive environments occur the metal alloy of fabrication of the heat exchanger equipment will be attacked, causing metal wastage and a loss of the metal wall thickness of the unit. If left unaddressed this can lead to leaks and a loss of containment.
Once the surface of the heat exchanger shell or tube sheet has started to corrode and pitting develops metal loss increases due to the iturbulent flow in this area, creating an even more aggressive erosion/corrosion cycle. It is therefore critical to ensure that the corrosion mechanisms are mitigated through corrosion management strategies, such as a surface corrosion barrier such as a high-temperature corrosion resistant alloy applied by IGS HVTS.
Prior Corrosion Mitigation Strategies
The operating conditions in heat exchanger units are highly varied, due to their common function and use throughout the refining process. Corrosion management strategies for the internal protection of reboilers and coolers have included the use of organic coating systems, weld overlay or build-up, and complete vessel replacement. Limitations exist with respect to the long-term durability of liquid epoxy coatings in this challenging environment, with repeat premature failure of the corrosion barrier, exposing the parent metal to the corrosive environment and leading to metal wastage and loss of the pressure boundary wall thickness. This often occurs prior to inspection and discovery at the next available shutdown or turnaround. Once this type of metal wastage has occurred, mechanical repairs to the unit are necessary leading to Heat Affected Zones (HAZ), Post Weld Heat Treatment (PWHT) requirements, and new locations at high risk of corrosion (weld seams, etc.). In addition, repairs are often costly and time-consuming due to the requirements to pull out and then replace the tube bundle when working on the heat exchanger shell.
This type of discovery scope leads to challenging repair requirements, a negative impact on shutdown schedules, the heat exchanger unit and hence the process availability. Turnaround time restrictions limit the feasibility and attractiveness of mechanical repairs or section / vessel replacement.
Upgrading the internal alloy with IGS High Velocity Thermal Spray (HVTS) coating solutions
IGS HVTS coating technology allows the process owner to upgrade the internal metal alloy of a cooling column or reboiler in-situ. In other words the section most at risk of attack can be protected, for example coating the tube sheet or bottom (or top) 1/3rd of the shell with a high nobility, highly Corrosion Resistant Alloy (CRA). To creates a new corrosion-resistant coating without the creation of HAZ or the requirement for PWHT.
The IGS HVTS noble coating is non-reactive and inert to the wide-ranging operating environments in heat exchanger vessels and columns. Specific alloys can be developed, freezing the metal condition and preventing any further internal metal wastage in your equipment’s unique environment. This technology, combined with the unmatched site experience of IGS, provides the asset integrity manager with a turnkey, long-term solution to corrosion.
Ongoing Inspection and Asset Integrity Assessment
IGS standard Quality Control (QC) practices include the final inspection of the work scope and the generation of an electronic thickness record with mapped electromagnetic stand-off gauge readings on a defined reference grid across the area of the corrosion resistant metal coating with HVTS. This record, as well as selected bench marked locations, are used for later inspections to confirm, in service, that the HVTS coating has maintained its integrity, and no metal loss had occurred (IGS has developed inspection technologies for external, on-line verification of the internal cladding integrity by through vessel wall scanning).
Unlike organic coating systems, HVTS metallic claddings are robust, long-term durable solutions with high mechanical toughness, abrasion, and steam out resistance and wide service temperature and pressure ranges. Their use can substantially decrease the vessel life cycle cost and can allow plant inspection teams to extend the required inspection intervals and vessel intervention on these critical pieces of process equipment.
The installation of IGS HVTS claddings as a corrosion mitigation strategy will reduce the future maintenance costs, repair requirements, and downtime of heat exchanger pressure vessels, ensuring their availability as required for the ongoing productivity of the plant.