DIPF Curve

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Maintaining equipment is a critical part of any business, and proper lubrication is essential for keeping machinery running smoothly. Unfortunately, many businesses struggle with the necessary knowledge to measure and plan proper lubrication. One method is the DIPF curve, which you can use in many ways to get the most out of your lubrication program. In this post, we’ll discuss what the DIPF curve is and how it can help you maintain your equipment.

What is the DIPF Curve?

The DIPF curve is the most common method to calculate frictional torque on a rotating shaft. It takes into account the effects of journal bearings, misalignment, and end-float. Knowing this calculation can help you improve lubrication effectiveness and overall equipment reliability.

The DIPF Curve vs. The PF Curve

The DIPF curve is a modern version of the PF curve. The PF curve is a potential failure functional failure curve. It was initially proposed to maintenance professionals in the Reliability-Centered Maintenance report by F. Stanley Nowlan and Howard F. Heap in 1978. The United States Department of Defense sponsored the report as a guide for equipment reliability management. The original design is a model for the most recent iterations of the curve, which reliability engineers are still developing and improving in response to a growing need to keep equipment running for as long as possible at the lowest possible cost of operation.

What are the DIPF Curve Components?


One of the most critical aspects of equipment health was missing from the original PF curve versions. The design component addresses issues such as:

  • Did you choose the right motor for your application?
  • Is the motor foundation structure secure enough to handle the motor forces?
  • Will the pump have plenty of head pressure to pump the fluid up and through the rest of the system?

Simply put, if you don’t design your equipment properly, it won’t be reliable. The reliability design phase makes or breaks the success of a reliability program and should not be overlooked. For equipment to last for a long time, it is vital to get the correct specifications.


Improper installation can ruin any system. The designed reliability from step one of the DIPF curve takes hold with proper installation. For example, take the same blueprints and build an identical house on sand and on a solid foundation. Which one will break down first? Even non-builders have an understanding that a structure is more reliable when properly built to specifications on a solid foundation. The same goes for your equipment.

To maintain a healthy, reliable system, you must follow proper installation methods. Proper installation ensures that the system is built with the intended level of reliability from the beginning. Alignment procedures must be followed, including thermal growth calculations and soft foot tests. Additionally, you should eliminate pipe strain in pumping systems. Finally, a reliability team member or a maintenance professional proficient in the system must conduct acceptance testing and verify the quality of the installation.

Potential Failure

Failure will happen no matter how carefully you plan a system or how flawless the installation was. The letter “P” of the DIPF curve designates a point where you can detect equipment failure rather than where it occurs. You should use predictive maintenance between the “I” and “P” of the DIPF curve. Also, you can trend data throughout this time to identify the point of potential failure. Numerous methods, including routine vibration analysis, temperature monitoring, oil analysis, and ultrasound data analysis, can assist with the identification of potential failures.

If an asset expresses conditions of potential failure, your maintenance team should take corrective action and increase the condition monitoring for that equipment. Corrective actions could be as simple as re-lubricating the bearings with the proper amounts of lubricant utilizing ultrasound data analysis. Or, they could involve replacing a worn-out coupling spider and confirming alignment.

During this time of increased condition monitoring, you will also be able to trend the rate of failure and make repair plans. It is nearly always less expensive to do a scheduled repair while the equipment is still functioning than to wait until it fails.

Functional Failure

The equipment stops generating the intended results once it reaches the functional failure (F) point on the DIPF curve. An example of this might be a motor that trips out due to an excessive current or a pump that loses flow and head pressure. When equipment loses core functionality, operational, monitoring, and repair costs all rise, especially with unplanned downtime. The increase in repair costs can be from paying overtime labor to get an asset back online quickly, paying rush shipping on replacement parts, or maybe paying a third-party contractor to handle the repair. This often raises the repair cost by 30% to 50%.

Another point of concern with functional failure is that the equipment’s potential for safety problems, such as technician injuries, rises as it becomes more unstable. With increased monitoring, the maintenance professional is frequently near the machinery, raising the risk of injury. To safeguard maintenance personnel and reduce repair costs, you should pull equipment when it enters the potential failure (P) zone rather than the functional failure (F) zone.

Catastrophic Failure

While it doesn’t have a place in the acronym for the DIPF curve, everyone experiences a catastrophic failure at some point. Even with the best maintenance procedures in place, it may still occur because of an abnormality or unknown defect. However, you will significantly decrease the likelihood of this occurring through the use of condition-based monitoring. When equipment reaches this stage, repair prices are the highest and downtime is the longest.

This is typically the time when choosing between repair and replacement is necessary. At this point, you would have to consider:

  • The Type of Equipment
  • Replacement Availability
  • Cost to Repair versus Replace
  • Timeframe to Repair versus Replace

Predictive maintenance and condition-based monitoring can help you avoid this point on the DIPF curve while improving costs, repair times, and worker safety.

The Benefits of the DIPF Curve

Building a strong condition-based reliability program, such as a predictive maintenance program, can be accomplished with the use of the DIPF curve. While the curve shape has changed, the overall objective—to save money and continue operating—has not. Always choose a planned repair over an unforeseen one to save money. You will be prepared with healthy equipment and a plan for when things go wrong by following best practices in each area of the DIPF curve.

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