Rotolining, or rotational lining, is a technology that allows engineers to bond thermoplastic polymer to the interior of tanks, vessels, pipes, pipe fittings, and other types of process equipment. The resulting layer of polymer adds corrosion protection and resistance to chemicals.
The rotolining process
Rotolining is applied via a rotational process. Workers place granulated powder resin inside the vessel or similar process equipment, seal all its openings, and then mount the vessel inside an oven. The oven rotates on two perpendicular axes at low rpm, giving the resin time to melt and spread uniformly over all interior surfaces of the equipment. The rotation of the oven causes the polymer to mold itself to the interior shape of the vessel. The treated equipment is slowly cooled to prevent shrinkage and warpage. Upon cooling, the polymer provides a seamless, permanently bonded liner.
Depending on the polymer used and the equipment’s service application, the thickness of a rotational lining ranges from 0.09 inches to 0.45 inches, thicker than most lining alternatives. A thick lining provides more corrosion and abrasion protection and maximizes service life of the equipment.
What is the difference between rotational lining and rotational molding?
In rotational molding, powdered resin is put into a mold, heated, and rotated on two axes to force the melted resin onto the sides of the mold. After cooling, the mold is removed, resulting in a hollow part formed out of the selected material. Rotational molding is commonly used to produce both industrial and consumer goods.
Rotational lining (or rotolining) is a similar manufacturing process. A pipe, tank, or other process vessel is supplied as the starting point, rather than a mold. The polymer is used to line the vessel and left intact.
Why use rotolining?
There are multiple benefits of rotolining solutions.
- Because the lining is monolithic and seamless, there are no weld joints to act as potential points of failure.
- The structural integrity of the equipment is maintained and even enhanced.
- Rotolining provides a seamless transition to a flange, making flanges easy to seal and reducing the risk of leaks.
- No other lining technique offers as wide a range of materials, allowing the material to be matched to its application
- Fully bonded liner can withstand vacuum and eliminate annular space for permeation to collect and condense.
- Operating temperatures are allowed through the full temperature range of the material chosen for the liner.
- Rotolining is suitable for a wide range of metallic substrates.
Limitations of rotational lining
A with any technology, there are situations in which a different solution would be better. Here are three limits of rotolining.
- Because the rotolining process requires the equipment to be mounted inside an oven, application is generally limited to straight lengths of pipe up to 20 feet long and vessels that will fit within a 12-foot sphere.
- Another limitation is that some internal structures, such as large baffles, are difficult to line.
- Unlike lining sheets, which can be installed in the field, rotolining must be added at the factory.
- Rotolining is limited to application on metal, including aluminum and carbon steel.
Polymers used in rotolining solutions
Polymer linings are selected depending on the application. Many polymers can be melt-flow processed including olefins, nylons, and fluoropolymers. A variety of these thermoplastic polymers may be selected to achieve the needed levels of chemical resistance, abrasion resistance, and corrosion resistance protection. Common materials for rotational lining solutions include:
- ETFE (Tefzel)
- PFA (Teflon)
- PVDF (Kynar)
- HDPE (high-density polyethylene)
One innovative material from RMB is HDPE blended with a biocide to deter the growth of biological films that can lead to microbially influenced corrosion when seawater is the process fluid. Over time, build up can even cause fouling of process lines, leading to costly maintenance
Proper polymer selection takes into account the compatibility of the material with the chemicals expected in the application. Other selection criteria include the material’s ability to bond with the substrate, its temperature performance, and of course, cost. The broad array of options allows engineers to tailor the lining to fit the needs of the application. Ultimately, the ideal selection of material will maximize the life of the treated equipment and reduce maintenance costs.
These materials must be formulated to enhance their ability to bond with surfaces. Teflon, for example, doesn’t want to stick to anything, so coupling agents are added to enhance adhesion. To prepare a surface for receiving a lining, the metal substrate must be clean and shot blasted to achieve a near white state. A clean and microscopically rough surface promotes mechanical bonding of the polymer to the metal.
What are the alternatives to rotolining?
When adding protection to process vessels and equipment, engineers commonly use sheet lining, powder coating, dual laminate construction, fusion-bonded epoxy (FBE), and loose linings of PTFE (polytetrafluoroethylene). Many of these have disadvantages.
Sheet liners and dual laminate liners have weld joints that create potential points of failure. Also, they have pressure limits and temperature limits lower than those of rotolined materials.
Compared to powder coating, a rotational lining is much thicker, reducing the chance of liner failure, and extending service life, especially in abrasive applications.
A rotomolded liner is tightly bonded to the substrate, in contrast to liners that are applied with adhesive. This makes rotolining useful under most vacuum services.
What’s more, powder coatings and dual laminate liners are not easy to repair, usually requiring the equipment to be removed from service.
Rotolining works well on complex interior shapes where powder coating is difficult and where a sheet liner may be difficult to install.
Fusion-bonded epoxy (FBE) is similar to rotolined polymers in that both materials bond with the metal substrate and create a seamless lining. However, FBE is limited to 0.04-inch lining thickness, and its application (similar to the application of powder coating) may be difficult inside equipment with complex geometries. FBE may be less costly, but often it provides a service life that is one-third that of rotolining, making the total cost of ownership far higher.
How Can RMB Help You?
Whether you are trying to minimize downtime because of a failed liner and need emergency services, need help to replace an asset during a future outage or are planning a new build, RMB can help. Simply reach out with your equipment type, service stream and dimensions and we’ll help you determine what solution best fits your needs.