Regal Beloit Corporation, is a manufacturer of electric motors, electrical motion controls, power generation and power transmission components.
Unplanned outages due to mechanical failures can cost millions of dollars of lost production time to Oil and Gas companies. While it’s difficult to quantify the cost of unplanned downtime, an outage of a single day may exceed ~$6.5M, for the average U.S. refinery1. The shift from Reactive Maintenance (RM) to data-driven Proactive Maintenance (PAM) strategies can not only reduce lost revenue from unplanned outages but reduce the overall costs associated with operating and maintaining plant equipment by 60%2.
Disc and diaphragm couplings are not a “wear item” like the seals in a turbine or compressor, which can cause a decrease in equipment performance and are typically replaced on a time-based schedule. Most high-performance couplings are designed to be maintenance free, and if they are operated within their rated capacities, can outlast the equipment to which they are connected3. To maximize production, each asset, critical or not, should have an appropriate maintenance strategy that is followed, audited for effectiveness, and adjusted as necessary to ensure reliability.
Criticality is a quantitative ranking process based on operational cost, maintenance cost, throughput losses, quality, safety, and environmental implications. The graph below represents the criticality distribution of the equipment at a typical plant (Figure 1). Only 10% of the equipment at this plant is deemed critical due to the costs incurred if placed out of service. 25 percent can be defined as essential. 30 percent is important. The remaining 35% is non-essential. Each criticality level can be paired with an effective maintenance strategy to balance the cost of implementation with the required reliability levels.
Following a criticality analysis, a Failure Mode and Effects Analysis (FMEA) is conducted to determine all the potential failure types, what the failure effect is, and what can be used to mitigate or eliminate the failure mode. The FMEA is then used as the foundation in the decision-making process to determine the correct maintenance strategy for new equipment. The most common maintenance strategies are listed below.
Disc and diaphragm couplings are designed for infinite life when operated within their application design limits; however, a change in operating conditions may a couplings service life4. The following sections highlight potential failure modes which can be mitigated or eliminated through the Kop-Flex Factory Recertification service. Used couplings are reconditioned to like “Like New” condition and returned with the original factory warranty, for a significant value over buying new5.
While recertifying high-performance couplings during every turnaround would be the most conservative maintenance strategy, it may not be the most cost-effective or feasible due to scheduling logistics. Guidelines which combine Factory Recertification and condition monitoring, with the understanding and prevention of past issues, yields an effective Proactive Maintenance strategy for your critical rotating equipment6. The following sections provide a foundational understanding of the Factors which may result in the reduction of the couplings effective service life.
While misalignment is typically not measured while equipment is in service, it is helpful to be aware of a few troublesome variables which can reduce the service life of the coupling. One of the most common questions regarding coupling alignment pertains to thermal offsets while operating. If the equipment and coupling are subjected to large temperature differentials, the accuracy of the thermal growth values is extremely important.
Was a hot alignment check of the equipment performed to mitigate against the unquantified movement between shafts and confirm the supplied values? Other difficulties in the determination of alignment while in operation may be due to a shifting foundation or pipe strain. Vibration monitoring or Root Cause Analysis (RCA) of a failed coupling can greatly assist in the identification and resolution of these issues. Factory Recertification can be utilized to reset the damage accumulation the coupling may have endured and return it to its “like new” condition.
Another factor which should be considered is the operating environment of the coupling. For many offshore applications, saltwater results in a highly corrosive environment which can accelerate the oxidation of ferrous metals. In some applications, the couplings are operated at temperatures well above the design rating due to guard design and unforeseen field issues. This higher temperature can affect the service life of the coupling. If these, or other environmental factors are true, the equipment inspection frequency should be adjusted accordingly. Factory Recertification returns the couplings service factor to the original, “as designed” value.