March 2021

Maintenance and Reliability

Strategies to minimize piping thermal maintenance system cost without compromising performance

Where process fluid must be maintained within a certain operating temperature window, the piping will likely require the application of a thermal maintenance system.

Forbes, B., AMETEK

Where process fluid must be maintained within a certain operating temperature window, the piping will likely require the application of a thermal maintenance system. Thermal maintenance systems can utilize a broad range of technologies—from bare tube tracing to fully jacketed pipe. However, regardless of the technology employed, engineering must be performed to design the system. The approach used for the engineering and design of the system can have a dramatic impact on the cost. This article presents four strategies for minimizing the total cost without compromising performance. The strategies are:

  1. Match the heating technology to the application
  2. Optimize the heating circuit lengths
  3. Optimize the utility infrastructure
  4. Structure the bid process to reward optimization.

In addition, three real-life examples are presented that demonstrate the actual savings that these strategies can achieve. These examples are:

  • Example A showing the benefit of Strategies 1 and 2 combined
  • Example B showing the benefit of Strategy 3
  • Example C showing the benefit of Strategy 4.

While much of this discussion centers around steam heating systems, the same principles apply to other heating fluids and cooling systems.

Strategy 1: Match the heating technology to the application

Different processes require different considerations in the design of the thermal maintenance system. The most common considerations are:

  • The purpose of the heating system: Liquids must often be maintained above a freezing point. However, for vapors, condensation within the piping is often a primary concern. In some applications, a pre-heat or recovery (melt-out) condition is the primary concern.
  • The acceptable temperature window: Some processes must simply be maintained above or below a critical threshold. Other processes have both an upper and lower bound that must be considered.
  • The available temperature differential: Some applications afford a large “temperature delta” that enables even a relatively poorly performing technology to be used successfully [e.g., maintaining a pipe above the water freezing point (0°C) using 10 barg steam (184°C)]. Other applications provide very little “temperature delta” and require a very robust heating system to ensure success [e.g., maintaining a pipe at 180°C using the same (184°C) steam].

Properly matching the heating technology to the application is key to reducing cost. An over-performing heating technology will cost more than a performance-matched technology. Conversely, applying an under-performing technology will necessitate the use of additional tracing runs and heating circuits, which will drive up the cost of the utility components. A properly matching technology will optimize both costs: (1) the heating technology itself will cost no more than what is necessary to achieve the purpose and (2) the utility infrastructure requirements will be minimized along with associated costs.

Many tracing technologies are available on the market. A true technology partner can help you select the best option without bias to any one solution. FIG. 1 is one example of a robust range of heating technologies.

FIG. 1. One example of a heating technology suite.

Technology 1a provides an eight times increase in heat transfer over tube tracing. Technology 2b provides a two times increase over Technology 1, as well as more consistent performance for critical applications. Jacketed pipe has no contact resistance; therefore, heat transfer is limited primarily by the convection coefficients of the fluids.

Strategy 2: Optimize the heating circuit lengths

Properly matching the heating technology to the application is only the first step. To keep costs as low as possible, the heating technology must be used to its fullest potential. Correctly sizing the system—in terms of the number of tracer runs per pipe length—is the most obvious aspect of this. However, it is equally important to maximize the length of heated piping between each supply and return point. Each of these heating fluid flow paths are commonly referred to as circuits (FIG. 2).

FIG. 2. Components of a steam tracing circuit.

The heating fluid loses temperature as it travels through the circuit. In the case of steam, the temperature loss is driven by pressure drop. If a circuit is too long, the heating fluid temperature towards the end will be too low to accomplish the thermal objective. One approach to avoid this issue is to conservatively limit the length of all the circuits. This approach is commonly the basis of plant tracing specification documents and is also often employed by tracing vendors to avoid the burden of additional engineering. This approach works because there are no technical concerns with having a circuit that is “too short.” However, it does require an unnecessarily high number of heating circuits, which then requires additional utility infrastructure, along with the associated costs.

A preferred approach is to establish each circuit length based on an actual calculated temperature drop. At a minimum, this calculation must be performed for each unique combination of process condition and lines size. Performing this calculation will create additional engineering cost, but that cost is more than offset by the savings achieved by using a reduced utility infrastructure. In many cases, plant tracing specifications are so conservative that using calculated circuit lengths can reduce the number of circuits fourfold.

Strategy 3: Optimize the utility infrastructure

Any heating system applied to piping requires periodic supply and return points. The location of these points is governed by piping geometry and the circuit length limitations. The resulting system will have supply and return points scattered throughout the facility. Proximate supply and return points are typically grouped together and connected to common supply/return manifolds (FIG. 3).

FIG. 3. Example piping system with circuit supply and return points.

Each manifold must be mounted at an accessible location and plumbed into the plant’s supply/return headers. The total cost of each manifold is significant, which is why it is desirable to keep the total number to only what is required. However, accomplishing this practically is a challenge. The hundreds of supply/return points and thousands of possible manifold locations form a jigsaw puzzle with millions of possible solutions.

The traditional approach is to scatter manifolds throughout the plant based on rough approximations and past experiences. The heating system supply/return points are then tied in wherever they can be. Where they cannot be tied in, last-minute manifold additions become necessary. Similarly, where manifolds or ports are not needed, the paid-for hardware sits unused.

A better approach is to match the manifolds to the circuits during placement. The goal of this approach is to minimize the number of manifolds by maximizing the number of circuits connected to each manifold. For example, the author’s company has developed a proprietary algorithmc that analyzes the supply and return points in 3D space and determines the optimum manifold locations that result in the smallest total number of manifolds.

This tool provides customers full flexibility to restrict the analysis to only acceptable manifold locations, to restrict the supply and return tubing length and to include existing manifolds in the analysis. With this tool, the resulting system design will always be the most optimal manifold placement solution.

The manifolds shown in FIG. 4 are the most common in steam heating systems. They are less common when the heating fluid is a liquid. Nevertheless, many of the same concepts of optimization can apply regardless of the specific supply and return hardware used.

FIG. 4. Example piping system with one possible manifold grouping indicated.

Strategy 4: Structure the bid process to reward optimization

The most powerful tool that can be used to control costs and optimize system design is to structure the contracts so these goals are rewarded. For example, in the case of a pipe heating system, the contract should reward the application of the three optimization strategies previously described. Two commercial mechanisms should be considered to accomplish this:

  1. Requires lump-sum bids—When a vendor is contracted to supply components at a per-unit rate, the vendor is not motivated to reduce the provided hardware quantity. Instead, vendors should be required to provide lump-sum bids that clearly define deliverables and performance guarantees. This motivates the vendor to minimize the quantities of hardware provided to maximize their profit. This approach will only be successful if the bid includes a commitment to well-defined deliverables and performance criteria. For pipe heating systems and associated hardware, consider requiring the vendor to supply the following:
  • A clear statement of thermal objective for each line (for performance accountability)
  • Calculations/thermal models justifying the quantity of tracers applied
  • Calculations/thermal models justifying the tracer circuit lengths specified
  • Detailed installation drawings for the tracing system and other supplied hardware
  • Field support for and inspection of the installation
  • A performance guarantee with defined corrective action
  • Material specification and fabrication standards for all supplied hardware.
  1. Consolidate scope to a small number of vendors—A vendor can only optimize what is within their scope. They do not necessarily have good insight into how decisions about their scope affect others. One vendor’s choice to optimize their scope may necessitate a disproportionate increase in another. A common example is tracing circuit lengths. The tracing vendor may be able to reduce their cost by using fewer tracer runs on the pipe by using very short circuit lengths. This can easily drive up the number of circuits, resulting in a disproportionate increase in the cost of the utility infrastructure. The solution is to consolidate the scope of supply to a smaller number of vendors. When one entity is responsible for the total scope, optimization decisions are made with consideration for the complete system. Like the first strategy, this approach is most successful when coupled with accountability to provide well-defined deliverables.

Cost savings

The savings achieved by these four strategies can be broadly categorized into three buckets:

  1. Savings achieved by reducing the quantity of hardware. Applying the engineered approach instead of conservative specifications will significantly reduce the number of parts required. This reduction is far more significant than any bulk buy or discount pricing effect could achieve.
  2. Savings achieved by reducing the number of last-minute purchases and project delays. The impact of this is much more difficult to quantify, but experience shows it to be significant. A project that is well planned prior to execution experiences fewer delays and surprises.
  3. Savings achieved by reducing the long-term operating costs. Long-term operating costs are primarily associated with energy utilization and parts replacement. Reducing the number of parts that comprise the heating system has a significant effect on both.

Example A: Optimizing technology selection and circuit lengths (Strategies 1 and 2)

The author’s company provided a heating system for a large, newly constructed, Canadian chemical plant. The plant design was like a previous plant that exclusively used bare tube tracing. It was initially expected that the same would be used in the new plant. The author’s company reviewed the basis of the technology selection and recommended two cost-saving changes:

  1. Use proprietary stream tracing Technology 2b instead of tube tracing on lines with more stringent thermal requirements (i.e., lines requiring many tube tracing runs)
  2. Establish circuit lengths based on calculated steam pressure drop instead of the previous plant specification.

Applying these recommendations resulted in an 89% reduction in the number of steam circuits (TABLE 1). Switching a portion of the project to proprietary Technology 2b increased the cost of the heating system but significantly reduced the number of circuits, providing an overall cost savings of 78% (TABLE 2).

The utility infrastructure includes the following components:

  • Steam supply manifolds and condensate return manifolds
  • Supply and return tubing for each circuit (tubing connecting steam supply/return manifolds to circuit supply/return points)
  • Steam trap for each circuit
  • Steam trap for each supply manifold
  • Fittings and hardware required to connect all the above components.

Note: In this example, proprietary Technology 1a tube tracing could have also been used as an intermediate technology between the tube tracing and the proprietary Technology 2b. Doing so would have resulted in additional cost savings. However, the customer chose not to pursue this option as they preferred the simplicity of using a smaller number of technologies. Additional utility infrastructure also creates additional operating expenses. These expenses take the form of additional steam consumption to support the extra heat load, and the form of additional maintenance cost to maintain the traps (TABLE 3).

The cost basis of this project’s individual items is summarized in TABLE 4. Note that this project utilized high-pressure steam, which required more expensive manifolds and steam traps. A more typical steam pressure would have resulted in lower utility infrastructure costs and lower operating costs for both options. The impact of this change on purchase cost would be relatively small, with savings shifting from 78% to roughly 76%. The impact on operating cost would be more significant, with savings shifting from $3.4 MM/yr to $2.1 MM/yr for steam cost and $454,000/yr to $175,000/yr for trap maintenance.

This and the following examples all use pre-insulated tubing to supply and return the heating fluid to the tracing. Pre-insulated tubing typically has a higher purchase cost than traditional hard pipe, but it provides significant time savings during installation.

Example B: Optimizing utility infrastructure (Strategy 3)

The author’s company provided a heating system for a major Middle Eastern refinery expansion project. The engineering, procurement and construction contractor had already placed manifolds throughout the plant before the author’s company was engaged on the project. The author’s company was asked to optimize the manifold utilization and applied its proprietary algorithmc. The expectation was that some portion of the planned manifolds would prove unnecessary and could be removed from the plan. This expectation proved to be true; optimization resulted in the removal of 15% of the manifolds and a total cost reduction of 43% (TABLE 5).

While the cost savings are significant, employing the proprietary algorithm on most projects will yield even more significant savings. Two factors affecting this project that limited the cost savings potential were:

  1. The planned manifold locations were based on a previous project for a very similar plant utilizing the same heating technology. Thus, the planned locations were actually very good approximations of what would be needed, much better than on an average project.
  2. Only manifold locations that were already planned could be used. The author’s company was engaged late in the project cycle. Planned manifolds could be eliminated, but adding manifold locations was not an option. Thus, the resulting manifold locations were not optimized to the extent that they could have been.

The cost basis of this project’s individual items is summarized in TABLE 6. 0.75-in. tubing is used for each circuit supply run and 0.5-in. tubing is used for each circuit return run.

Example C: Optimizing the bid structure (Strategy 4)

The author’s company provided a bid for another major Middle Eastern refinery expansion project. This bid included the application of all three optimization strategies:

  1. Optimization of technology by using a combination of tube tracing and proprietary Technology 1a in place of tube tracing alone.
  2. Optimization of circuit lengths via engineering calculations.
  3. Optimization of manifold quantity and placement via a proprietary algorithmc.

The lump-sum bid was being compared to another vendor’s per-unit bid. The end user chose to use the other vendor due to the lower apparent per-unit cost and the relatively late engagement with the author’s company. After the project was completed, the author’s company was provided a tabulation of the actual hardware used on the project. Unsurprisingly, although the project scope had not increased, the number of components used was considerably higher than what was initially estimated. The final cost of the as-built system far exceeded the author company’s lump-sum proposal (TABLE 7).

The per-unit pricing created a motivation for the vendor to allow the project scope to balloon. A lump-sum bid would have ensured that costs increase only in response to a legitimate expansion of scope. By using the lump-sum approach, the end user could have saved 50% on the project.

The cost basis of this project’s individual items is summarized in TABLE 8. The as-built system utilized a combination of 0.375-in., 0.5-in. and 0.75-in. tube tracing. The optimized system utilized a combination of 0.5-in. tube tracing and the proprietary Technology 1b.

Takeaways

Controlling the cost of a thermal maintenance system requires the vendors to apply an engineered approach. The key focus of this engineering approach is to:

  1. Match the heating technology to the application
  2. Optimize the heating circuit lengths
  3. Optimize the utility infrastructure.

To ensure that the vendor(s) applies this approach, the bid should be structured in such a way that optimization is rewarded. This is accomplished by:

  1. Requiring lump-sum bids with well-defined deliverables and performance criteria
  2. Consolidating the scope to a smaller number of vendors to achieve cross-discipline optimization.

To best capitalize on these strategies, look for a technology-neutral thermal maintenance system provider with strong engineering capabilities. HP

NOTES

      a Controls Southeast Inc.’s (CSI’s) TraceBoost technology
        b CSI’s ControTrace technology
        c Manifold Optimization Scheme

The Author

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