Preventing Inlet Erosion in Shell & Tube Heat Exchangers
In July 2011, after several years of experiencing dwindling operation efficiency and increasing retubing costs, a major ethylene production facility in the US tasked HydroPro with finding a solution to their tube inlet erosion problems on their Transfer Line Exchangers (TLEs).
Traditionally, the plant would pull the units offline in 4-6 month cycles in order to clean and make repairs. Most often a handful of tubes would be plugged due to severe inlet erosion and then the units would be put back into service until too many tubes were plugged or it had to be retubed. With six sets of TLEs, plus a back-up set, the plant was retubing 1-2 TLEs per year. Each set consisted of two shell and tube heat exchangers.
HydroPro posed a potential solution to combat the issue; sacrificial sleeves would be installed at the inlet to protect the parent tubes from erosion. Following the same 4-6 month cleaning and inspection cycle, the sleeves would be inspected along with the rest of the unit and be replaced as needed. This allowed any necessary changes to be made to the design and/or placement of the ferrules. Sleeves (or ferrules) are typically a thin walled tube, that will be inserted into the parent tube and hydro-formed into place. The idea would be that these ferrules would be expanded into place using HydroPro’s SleevePro expansion system, which hydro-forms the sleeve into full contact throughout the length of the sleeve, and a mechanical roller to “blend” roll the ends of the sleeve and close off any gap at the tube end.
The sacrificial sleeve OD was selected using actual measured tube IDs from the in-service unit. The wall thickness and material were determined by the end-user’s metallurgists and a heavy wall, 1-5/8” x 0.120” AW SA249-304H material, roughly 6” in length with an entry flare was selected thanks to its compatibility with the unit’s SA209-T1A parent tubes and process gas. Ensuring the client’s engineering team assisted with the material selection was imperative in preventing potential issues caused by galvanic corrosion or dissimilar metal separation during unit operation.
While a 0.120” wall thickness is considerably higher than most ferrule applications, the inlet erosion experienced by TLEs can be severe. It was also determined that the “problem area” consisted of approximately 36 tubes in the center of the exchangers where the high temperature gas entered the exchanger like a cyclone and rapidly eroded the tubesheet face and tubes, so this would be where the sacrificial ferrules would be installed.
Lastly, to test the feasibility of the process and determine any associated loss of efficiency from installing a heavy-wall ferrule, the initial installation would be performed on only a single set of exchangers (two shell and tube heat exchangers per TLE), and its next inspection would determine whether any changes needed to be made to the preventative maintenance plan.
Within a few days of finalizing an action plan, the first set of seventy-two sleeves were installed. After a month in operation, when asked which unit had been sleeved, the engineer said he couldn’t tell and would have to look at the documentation to confirm which set the ferrules had been installed in. He had found that there was no discernable loss in efficiency when using the heavy-wall sleeves and was looking forward to seeing what sort of protection they’d offered from their erosion problem during the unit’s next inspection.
Fast forward four months to the first scheduled inspection; the client was so pleased with the outcome that they ordered all of their TLEs to have the sacrificial sleeves installed in the same manner. This work would be completed over the course of the next two years as the units were pulled down for cleaning on their regular maintenance cycle, or as the units returned from a previously scheduled retube.
The most interesting thing, however, is the fact that HydroPro wasn’t asked to remove and replace any sleeves until February of 2013. The plant didn’t require swapping of sleeves due to erosion for more than 18 months on the first set of units, and with no discernable loss of efficiency. In fact, over the course of the 4 years where this project was closely monitored and handled directly by HydroPro, the 7th set of TLEs (the back-up set) hadn’t been put into service a single time and not one of the units had to be retubed. A big change from the average of having one to two TLEs offline for retubing each year.
HydroPro’s solution offered the plant an opportunity to reduce costs associated with plugging and retubing, and increase overall efficiency by keeping tubes in service for two to three times longer than before. The ferrules proved to be a viable solution for preventing erosion of the parent tube material and was added to the plant’s standard inventory for preventative maintenance moving forward.
For more information of HydroPro's sleeving solutions, visit www.hpro.com/sleevepro. To learn more about HydroPro's solutions for extending exchanger life or to discuss your specific requirements, they can be reached at firstname.lastname@example.org or (573) 732-3318.