Preventative Maintenance Best Practices – Replacing Spring Support Audits with Pipe Stress Audits

December 06 17:58 2019

Piping Technology and Products has a unique perspective on best practices in preventative maintenance. PT&P has a database built from over 1,000 audits performed in 41 countries. PT&P also has experience from over 3 Million pipe supports and expansion joints currently in service.

The design of the piping system is a major part of the engineering of an operating plant build. On average, piping constitutes 40-48% of the engineering hours in a new refinery. The challenge facing piping engineers is rotating equipment locations and process design are defined and the piping engineers must make the piping system fit within the designated space while dealing with thermal stress, proper flow, and allowable loads for all equipment. With temperatures in high energy lines often well over 1,000 degrees, this can be very challenging.

The following are some of the goals of pipe stress engineering and the placement of spring supports and expansion joints in the piping system: ensure stress at the interface to moving equipment is below maximum allowable loads, minimize turbulent flow through the piping system, and ensure the longevity of piping system components.

Operating plants tend to follow one of three strategies with their spring supports:

A. Only fix spring supports when something is wrong

  • Pros
  1. Maximize short term cash flow
  2. Potentially moves financial impact from Opex to Capex
  3. Limits overspending on preventative maintenance
  • Cons
  1. Likely leads to allowable stress being beyond max for some moving equipment
  2. Will lead to maintenance issues with moving equipment
  3. Can lead to premature failure of piping system
  4. Could lead to a plant shut down

B. Perform regular inspection and replace damaged spring supports

  • Pros
  1. Insures broken spring support are replaced prior to causing issues
  • Cons
  1. Does not ensure the proper functioning of each spring without adjusting Spring Supports which are out of position

C. Periodically return piping line to its original design specification and/or set new design standard if the design has changed.

  • Pros
  1. Ensures the system is brought back to original design minimizing strain on moving equipment Potentially moves financial impact from Opex to Capex
  2. Minimizes stress on the piping system
  • Cons
  1. Higher short term expense Will lead to maintenance issues with moving equipment
  2. The business case can be challenging due to the medium/long term nature of savings
  3. Potentially more Opex vs Capex
  4. Minimizes risk of an unplanned outage

PT&P has seen many examples of each of the strategies above. Typically, the strategy taken at an individual plant is closely related to overall operating philosophy of the organization, including finance. However, we also speak to a number of organizations who have placed an emphasis on preventative maintenance but are not sure of the best practices for the engineered pipe supports and expansion joints.

For preventative maintenance, best practice is to not just focus on the health of the piping system components, but on the health of the overall piping system. The following are some of the issues that PT&P has found that cause system level issues:

  • Spring Support Failure Impact – the failure of a spring support will impact other supports and cause them to possibly fail as they attempt to take on the additional load of the failed spring
  • Damage to Piping or Rigid Supports Changes Elevation of Spring Supports – a variety of issues can cause the piping to undergo strain, which causes deformation. This will cause a change of elevation or distance from the pipe support to the pipe and impact the load setting and connections to other equipment
  • Improper Travel Stop Management – if travel stops are not removed, the spring supports are essentially a rigid support, and the load can be redistributed among the spring supports on the same line in a way that is not consistent with the original design
  • Improper Initial Installation – one of the most common issues PT&P finds in its audits is that engineered supports are improperly installed during initial installation

By the time a plant reaches 10+ years of age, PT&P’s experience is that most plants have encountered one or more of the issues above. For this reason, it is essential to take an approach of resetting the line to the original design specification. Best practices for performing a “reset to design specification” are the following:

  • Hot and Cold Audit – required to understand the range of movement
  • View of Functioning of Springs/Expansion Joints Across Line – the view of how a spring is functioning can be highly dependent on whether there are many failed supports on the line versus just one
  • Plan for Adjustments and Replacements – the overall plan for a turnaround must be comprehensive in terms of adjustments
  • Proper Management of Travel Stops – we have found tremendous confusion on the proper timing for placement of travel stops; if this is not done correctly, in many cases it is not possible to reset the line to the original design specification
  • Repair Rigid Support Issues – a common issue we have run across is a damaged or removed pipe shoe or saddle resulting in the piping sitting on the supporting pipe rack
  • Assess Elevation Changes – changes in elevation due to changes or deformation of piping can cause a spring support to be out of position; this issue should be addressed as an issue with the line rather than the spring support
  • Identify Design Changes – PT&P sees many situations where there have been alterations to the line, such as new equipment without an update of the stress analysis; the best approach is to redo the stress analysis; however, the budget or time constraints may require a quick and dirty approach such as weighing the line
  • Adjust in Real Time as Needed – Given all of the issues above, resetting a piping line to design specification takes real-time decision making during an audit

The challenge with this approach to preventative maintenance is that it takes a much deeper level of expertise than a component level inspection. PT&P’s experience is that even the ability to operate a pipe stress modeling software program such as CAESAR is far different than a pragmatic understanding of the proper functioning of all the elements of the piping line. Many personnel and firms supporting piping system maintenance are challenged with managing a broad range of equipment at an operating plant, and this can make it difficult to have the depth in pipe stress that may be required to properly execute a system level audit and execute a plant to return the piping system to the original design specification.

The sole purpose of performing audits is to maintain the piping system and equipment to remain in the proper condition. Therefore, the system level (pipe stress audit) that considers the physical condition of the system, along with the spring supports system should be preferred. As mentioned earlier, the component level audit is an important part of the system level which if put together with other system and/or deformation assessment can give the overall picture of the system and finally a better direction for the proper maintenance.

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Company Name: Piping Technology & Products
Contact Person: Rosemary Reynolds
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Phone: 7134524846
Address:P.O. Box 34506
City: Houston
State: Texas
Country: United States