Fig. 1: An example of so-called tube tracing.

Bolt-on tracing – an overview

In many process sectors, media in pipes, vessels and tanks needs to be heated in order to prevent corrosion, to maintain a stable viscosity, to prevent product degradation due to crystallization, etc. Over the years various heating options have become available, such as steam which can be passed through tubes inside the equipment or through an external jacket, the use of electrical cables, etc. This article focuses on a more recent development, namely bolt-on tracing.
 
In this author’s experience, practically any piece of equipment or process component can be economically heated with a bolt-on tracing system. Individual components like pipes, flanges, fittings, valves, and instrumentation can also be provided with bolt-on jacket.

Thanks to its ease of use, as well as the fact that the system provides the thermal performance necessary to meet project specific requirements, bolt-on tracing is being increasingly turned to in applications such as delayed coking, solvent de-asphalting, urea, caprolactam, polymers, sulphur recovery etc.

In this article we will see an overview of this bolt-on tracing system and its advantages over the conventional system.

Conventional systems

Steam tracing is usually achieved by running steam lines in direct contact with the piping or vessels to be heated. The entire assembly is then insulated to direct the heat into the process fluid. This is the traditional method; however, it has its drawbacks & concerns, such as limited heating capacity and reliability.

Figure 1 shows an example of so-called tube tracing. Here, the steam flows through ∞” pipe/ tube which is banded onto the piping which has to be traced.

An alternative is to create so-called steam jackets. As shown in Figure 2, this technique consists of an inner process line which passes through the contra of a large diameter steam line. The outer jacket pipe is welded to the back of the end flange (modified) of each jacket section. The inner pipe is welded into the modified flange.

The main drawback with steam jackets is their cost. Bolt-on tracing delivers equivalent performance with lower purchase costs.

Bolt-on tracing

This method used rectangular tubing which is fabricated to fit closely to the contours of the pipe, etc, which needs to be heated (see Figure 3).

The starting point for fabrication can be a 2” length of boiler tube which is deformed into a 2”x 1” rectangular section. One side is then shaped to match the outer diameter of the component to be heated. Bolt-on tracing components are normally designed according to ASME Section VIII.

The heating medium (steam) flows through the rectangular tubing. Heat transfer cement or mastic is used to fix it to the bare pipe. However, it can also be strapped into place. To achieve the best target temperature, more elements can be added.

Advantages of bolt-on tracing system:

When compared to jacketed piping, bolt-on tracing offers the following advantages:

  • Cross contamination free: as the bolt-on system does not require welding to the equipment to be heated, there is no chance of any cross contamination caused by corrosion or welding-failures
  • It is engineered to suit project specific requirements and product performance is guaranteed by vendor. It is based on thermal analysis
  • There is less steam consumption and no steam wastage/leaks
  • Process pipes can be butt welded and do not required flanged spools need for jacketed piping
  • All in-line components remain line-sized
  • Far fewer expansion loops are required. The stress analysis is reduced to just a single calculation
  • Easy to install and easy to modify retroactively should the process later require revisions or changes
  • Easy periodical maintenance of the steam traps

When compared with tube tracing, bolt-on tracing offers the following advantages:

  • It is engineered to suit project specific requirements and product performance is guaranteed by vendor. It is based on thermal analysis
  • Less expensive (capex) in circuitry because fewer steam traps are needed
  • Less circuitry results in fewer steam traps and in less overall maintenance cost (opex)

Hot-oil tracing

So far we have only considered bolt-on tracing which uses steam to heat the pipes, or equipment. However, hot oil can also be used to good effect. In a hot oil system, factors such as thermal requirements, heating medium routing, flowrate, and heat load must be considered to meet the thermal objective. The hot oil system benefits include the broader temperature range (-50 to 600F) and lower operating pressures compared to steam. A typical system layout includes the following: pump, heater, supply & return header, and heating circuits with applicable flow control devices.

Conclusion

Around the world, process technology licensors, EPC companies, and end users all appreciate bolt-on heating systems as a key element in solving tough heating challenges such as in the sulfur industry. Bolt-on tracing has been successfully used since at least the 1980s.

References and images

When researching this topic, the author consulted websites of some of the industry leaders in bolt-on tracing, including CSI (www.csiheat.com) and ThermEx (www.thermex.be). The author recommends reading these pages to keep updated on the latest industry trends and knowledge.
 

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