Exchanger Tube ID Coating

History of Small Tubular Coating Technologies

Exchanger tube coating (tube lining), as we know it, began in Europe in the mid-twentieth century, using a “flood and drain” method to coat tubes with phenolic materials. This remained the only option until the mid-1980s, when spray applications were first tried.

Using air pressure to atomize material, exchanger tubes were coated with a spray application of engineered polymers. This technique proved to be much simpler and less time-consuming than the fill/drain/rotate method prevalent at the time. With the development of this patented method, Curran International changed the industry standard for exchanger tube coatings, applying the polymer tube lining system to the full circumferential inner diameter (ID) of a small tube with a uniform, homogenous layer of material. Curran’s exchanger tube lining can be done in our Houston, Texas shop or on-site around the world. Both U-tube and straight tube exchangers can be coated with the protective lining.

Typical turnaround for a 1,000 tube ¾” OD by 20 ft long

  • 3-4 weeks in shop (under 2 weeks for expedite)
  • 1-2 weeks with dedicated crew on-site

This system was first demonstrated in the U.S. at a Florida power utility, where through wall corrosion in the piping had prematurely shortened the life of a steam condenser. The utility, together with the Electric Power Research Institute (EPRI), began to research epoxy coatings for tube IDs as an alternative to costly, time consuming alternative methods of repairing their condenser.

The study verified the efficacy of tube lining, which proved less susceptible to fouling compared to uncoated tubes. Exchanger tubes with coatings also held up under sustained heat transfer better than uncoated tubes.

The economic benefits rapidly gained traction when petrochemical refineries applied thin film coatings (thin film tube lining) to the tube id’s in its heat exchangers. Refineries with “bad actor” exchanger bundles found that thin-film polymer coating eliminated normal maintenance as a result of reduced foul attachment and corrosion deposits. This in turn improved operational efficiency and favorably impacted profit margins.

Curran International patented its spray applied exchanger tube lining system in 1996. Its many clients include the major refineries and power-gen plants around the world.

Thermal conductivity

Thin film polymer tube lining materials, applied at 10-12 mils or 250 microns, provide a foul release suited for all water services. The application technique achieves a homogenous film, and complete coverage is ensured through 100% inspection according to NACE standards.

Exchanger tube coatings (exchanger tube linings) have proven to reduce fouling and boundary layer drag. By promoting flow, backpressure is reduced and the long-term optimal performance of heat transfer equipment is sustained. Coatings are chosen according to the service temperature and conditions in which they are to be applied, as well as where – in the field or in-shop.

Application capabilities include polymerized thermosets and thermoplastics, thick film epoxy cladding, ceramic and glass filled linings, rubber and sheet linings, and inorganic “metallized” linings.

U-Tube exchanger coating

U-tube exchangers can also be coated. In fact 45% of exchangers coated at Curran’s shop are U-tubes. The only difference is that a flow coat application is used.

Used exchanger tube repair

Curran’s method for applying exchanger tube coating can also be applied to used exchanger tubes to repair them. Curran can repair your exchanger tubes, by removing all of the scale from the tube wall (including deep pits) and applying its tube lining system to cover those pits and the tube wall. What you are left with is a fully enclosed coating system that will prevent any further corrosion, and will also eliminate fouling. Click here to receive a quote to repair your exchanger tubes

Bottom line

Application of polymer coatings to the ID of pipes in heat transfer equipment can:

  • Increase heat transfer duty
  • Eliminate corrosion
  • Reduce or eliminate micro and macro fouling
  • Reduce normal maintenance and improve the “useful life” of fixed assets.

Some chemical exposures, elevated temperatures or high fluid/gas velocities can limit coatings, but great benefits can be achieved by applications within acceptable temperature parameters and exposures appropriate to the applied coating.

The many advantages of coating tubular systems include

  • Cost savings that can amount to millions of dollars per year (See paper presented by gulf coast refinery at NACE 2005)
  • Perpetual equipment life
  • Energy savings
  • Throughput efficiency gains
  • Savings in comparative cost of entirely replacing tubing with expensive steel alloy pipes.
  • Exchanger coatings can eliminate any copper discharge.

Typical application procedure

  • Exchanger tube are cleaned of all fabrication oils
  • Exchangers tubes are grit blasted to clean tubes and create a surface profile (verified with a video probe (Pits in used exchangers tubes are verified clean with video probe)
  • Exchanger tube lining process begins and multiple coats are applied to achieve the mils and a pin hole free application
  • The tube lining of each tube (100%) is spark tested to confirm a pin hole free application
  • Repairs (if necessary) are made to any portion of the exchanger tube lining that had a pin hole indication
  • Those repairs are tested again
  • The exchanger is shipped back to the client

 Thin Film Engineered Polymer Coatings

Curran 1000 T Hybrid Epoxy – Amine catalyzed, ambient cured coating system, shop or field applied, for exchanger tubes in water-side operating environments to 365F (185C); dispersion application method, 8-12 mils (200-300 microns) total DFT. May be used for “in-service” equipment and “in-situ” repair of corroded condenser tube IDs.

Phenol Epoxy – Amine catalyzed, ambient cured coating system, shop or field applied, for exchanger tubes in water-side operating environments to 250F (130C); dispersion application method, 8-12 mils (200-300 microns) total DFT. May be used for “in-service” equipment and “in-situ” repair of corroded condenser tube IDs.

Saekaphen (GmbH) – Heat catalyzed, shop applied thin film tubular coatings; offering strong resistance in either acidic or alkaline services, wide Ph, service temperatures to 300F (150C); flood and drain application method, 6-10 mils (150 to 250 microns) total DFT.

Novolac Epoxy – Shop or field applied, primary coating for U-tube exchanger bundles; wide Ph resistance for storage and transport application; suitable for water immersion to 260F (127C); flodd and drain application method, 8-14 mils (200-350 microns) total DFT. Coating may be applied to 60 mils (1500 microns) DFT, for channels and heads.

Curralon ® – PPS proprietary-blended thermoplastic, shop applied and heat cured; wide chemical resistance, wet H2S, HCL; immersion resistant in geothermal fluids, and acids to 400F (200C); requires bond coat pretreatment; contact Curran prior to specifying.