Combine Murphy’s law with bad timing, and you’ll get some idea of the situation faced by NOVA Chemicals, Inc., when a critical process fan went down during a sleet storm. Add in the “every cloud has a silver lining” adage and you get the story of how one very negative situation ended on an extremely positive note through SKF Service and fan expertise.Located in Monaca, Pennsylvania, NOVA Chemicals is a manufacturer of expandable polystyrene and specialty foams. A key process in the company’s 3 ½-mile-long plant is the Pentane Emissions Recovery System (PERS). Within that system, a critical piece of equipment is the PERS induced draft fan, which extracts and recovers pentane vapors from the process areas.

   Earlier fires in the fan had distorted the fan casing, a problem that NOVA Chemicals fixed temporarily by using jack bolts to hold the casing in place. The fan continued to have problems, and on a cold night, during an ice storm, the jack bolts broke and the fan went down.

   “When that fan is down, the costs mount up,” says NOVA Chemicals Reliability Team Leader John Dudo. “We have a back-up fan, but that costs us $3,000 a day in additional operating expenses to run. So, it’s an extremely expensive situation when we lose our main PERS fan.” Dudo explained that the fan was scheduled to be down for permanent repairs to the distorted casing along with its regular three-year maintenance just three months later. “When the fan went down, we had to perform emergency fan repairs, knowing we had to keep it going for just a few months,” he said. NOVA Chemicals mechanics did just that, installing new bearings and other components on their own in the worst of weather conditions.

   Although the NOVA Chemicals team’s quick fix was working well enough, high bearings temperatures and other problems continued to plague the system. Hoping to avoid a longer than necessary outage during the scheduled maintenance, and to eliminate ongoing problems once the fan was back up, Dudo acted on a suggestion made by the company’s equipment supplier, Fred Kull of Applied Industrial Technology. Kull recommended that NOVA Chemicals take advantage of SKF Service, a relatively new capability offered by SKF. The result: “Their fan is now running like a Swiss clock,” says Kull.
   
For NOVA Chemicals’ John Dudo, the “silver lining” presented by his fan troubles, was becoming aware of the broad service and technical support capabilities offered by SKF Service. “They analyzed our system, suggested a better bearing configuration, installed it, and followed up to make sure it was running properly,” he notes. “I simply didn’t know this kind of comprehensive support was available.”

SKF Service: taking productivity to a higher level
An extension of SKF’s Trouble Free Operation (TFO) program, SKF Service was developed to provide industrial facilities with a full menu of reliability-related services and products focused on enhanced productivity. The capability pulls together SKF’s extensive knowledge of bearings, seals, lubrication, maintenance products and condition monitoring.

   “Bearings are the key interface between moving parts,” says SKF account manager Steve Kelly. “They’re literally the diagnostic heart of the machine. Misalignment, unbalance, looseness and friction are all telegraphed through the bearing.” Kelly explains that while most bearing companies will recommend and supply what they feel is the right bearing for the job, SKF goes far beyond that in terms of technical expertise and support.

   “We analyze the information coming from the bearing, look at the total system, recommend the right product, provide a precision installation, and follow up on regular intervals to make sure everything is performing as expected,” he says. “We view bearing applications as a key component in helping our customers raise productivity, and lower costs.”

For NOVA Chemicals: a plan for PERS performance
“Our intention in calling Steve Kelly and SKF in was to have a failure analysis done on the bearings removed during our emergency fix,” notes John Dudo. “We just wanted to be ready to do the upcoming installation the right way and quickly.” Steve Kelly and SKF Service manager Dan Donnelly instead recommended a complete analysis of the fan application with the goal of enhancing performance and reducing the total life-cycle cost for the fan. They suggested a Mechanical Reliability Assessment (MRA) to identify key operational targets and performance indicators.

   A multidisciplinary team of SKF Service experts, including Maintenance Reliability Specialists Mark Frogley and Greg Pavlov, Fan Engineer Mark Hinckley, Account
Manager Kelly and Service Manager Donnelly, performed the assessment. The team
conducted an in-depth analysis of the fan, including bearing shaft and housing diameters; plates, pedestals and grouting; impeller vanes; lubrication specifications; bearing arrangements; and alignment and balance.
   
“We saw that the main factors affecting performance in the PERS fan were the thermal changes created by the varying hot gas temperatures,” explained Mark Hinckley. “The heat conducts down the shaft, making the shaft continually expand and contract, impacting the bearings.” NOVA Chemicals had been using spherical roller bearings, a common product for industrial fans, but one that requires that the outer ring of the bearing be able to slide axially inside the housing in response to the axial expansion of the shaft. Even with a loose-fit housing, friction between the bearing and housing can result from radial loads generating axial (thrust) force within the bearing system. This thrust force can create vibration and high temperature, and lead to reduced bearing life.

The SKF Solution: CARB Bearings and System 24
SKF Service’s team suggested replacing the spherical roller bearings with Compact Aligning Roller Bearings (CARB), a breakthrough technology recently introduced by SKF. CARB toroidal roller bearings accommodate axial displacement and angular misalignment, and have greater load capacity. “We suggested CARB bearings primarily because they float internal to themselves, “says Hinckley. “That allows for frictionless thermal expansion in the fan.” CARB is a purely radial bearing, and cannot carry any axial loads. It accommodates the axial expansion within the bearing itself, with negligible friction, at the same time as it allows misalignment. So, the typical high vibration levels, elevated temperatures, and reduced bearing lives seen in fans are avoided.

   The team also recommended the SKF System 24 automatic lubrication system. “By ensuring the fan bearings received the right quantity of lubricant at the right time, we knew we could do a better job of maximizing bearing life in this application,” says SKF Maintenance Reliability Specialist Greg Pavlov.

A precision installation
The rebuild of the PERS fan presented John Dudo with a tough situation in terms of manpower and timing. The plant runs around the clock in a sold-out condition, so the outage timeline was critical.
   “We had previously scheduled 14 days for an outage,” notes Dudo. “But due to our sold-out situation, the outage was reduced to just seven days.” Adding to that pressure was the fact that during the outage, the plant also had a shortage of manpower within the maintenance department. “The availability of SKF technical guys to do the installation for us was the solution we needed.” he says. “They completed the job and the system was turned over to operations two days ahead of schedule, reducing the timeline on the fan repair to just five days.”

   But the SKF team did more than simply install the new bearings. “The whole spirit of SKF Service is total system reliability,” says Dan Donnelly. “When a fan or other machinery is taken apart, our guys look at the whole system, search for root causes of problems and identify potential problems. They’re not just wrench turners – they actually diagnose the system and improve reliability.”
   
John Dudo was impressed by the expertise of the installation team, citing the outstanding work of SKF Reliability Maintenance Specialist Mark Frogley. “Mark and his guys did an excellent job,” he notes.
   “They checked the whole system, made sure everything was precisely aligned and balanced, and checked the clearances on the bearings after the installation.”

Resonance analyisis
SKF Service went one step further to help NOVA Chemicals bring the fan to peak performance levels by offering to analyze a resonance problem. The fan is a variable speed fan that normally runs between 400-900 rpms. The fan had two critical speeds, one at 340 rpm, the other at 760 rpm. “760 rpm is where the fan tends to sit during our process and that’s exactly where we were experiencing a lot of vibration,” explains Dudo. During the emergency quick fix, Dudo had changed the inlet/outlet expansion joint from a rigid joint to a flexible joint. He believed the problem had improved but wanted a more definitive analysis of what was happening.

   Mark Frogley suggested further testing the system through an Operating Deflection Shape (ODS) analysis of the backside of the fan casing. ODS is a technique used to provide a visual representation in the form of an animation of how measured points on a structure are moving relative to each other. The data is reported as an active movie file, which can be viewed using Microsoft Media Player. In addition to the animation, absolute magnitudes and phase are collected at each data point on the structure, quantifying the structure’s movement.

   “The ODS survey confirmed that the joint was working,” says Dudo. “It also provided additional recommendations for the supporting structure to improve the life of the fan.”

Ongoing service and support
Six months after the fan rebuild was completed, SKF was back at NOVA Chemicals, checking on the performance of the bearing configuration. “They took the bearing caps off, gave us recommendations, and provided a detailed report,” says Dudo. “The follow-up service was great.”

   “I’ve always believed that SKF had a good name and a good product,” Dudo adds.
   “But I had never considered them for this comprehensive level of service before. Overall I was very impressed.”
   
According to Dan Donnelly, this kind of reaction is typical with the new SKF Service capability. “We get called into tough situations and come out with everyone feeling completely positive about how much we can do for them and the value we’re able to create,” he says.

   For customers like NOVA Chemicals, the benefits go beyond problem resolution.
   The availability of SKF Service also provides a powerful defense against the unpredictable challenges of Murphy’s Law, bad timing and clouds without silver linings.