Heat tracing

Introduction

Heat tracing used widely in Oil and Gas industry. Tracing used around pipes and/or equipment. This technique used for places with cold weather or where the product is not allowed to be cooled down. The cover picture shows heat tracing around a pump. As for equipment heat tracing can be installed around the equipment or inside them if the manufacturer knows the data beforehand.

Heat tracing used in bulk material transfer

Every day around the globe, millions of tons of materials are transferred from a place to another. There are many ways, each with its pros and cons; such as trains, trucks, and also a network of pipes with compressors for gases and pumps for liquids.

In a refinery plant, often it is required to move material (Solid, Liquid, or Gas) from a point to another and there are many methods to achieve this goal. One of the methods that used particularly for solids is liquefication. An example of this phenomenon is Urea. Urea melts at ~140°C. Thus it can be transferred with a pump instead of elevators or conveyors at normal temperatures. However, the most important part that a designer shall consider is solidification. In this article we cover heat tracing as general and then a case study for a Urea pump. One of the usages of heat tracing is solidification prevention.

Heat tracing methods

There are two main methods of heat tracing, by using material (such as hot water or steam) or by using electrical energy. Each method has its pros and cons.

Steam or hot water:

In this method heating tubes installed around or even inside the casing of the Equipment. As hot water or steam flows inside these canals, Equipment’s temperature starts to rise and reach the desired temperature. At the refinery plant, LP (low pressure) steam is available. This type of steam is produced as the exhaust of backpressure turbines or the product of a process. It is not economical to use this steam to power a condensate turbine thus LP steam is a waste. So it is logical to use this steam as heat tracing. Another pro of this method is independence from electricity. This means during emergency cases, the heat tracing does its duty and prevent solidifications in pipes or in equipment. The cons of this method are corrosion and blockage. Hot water and steam are corrosive, this results in corrosion over the years or the change of construction material, which means higher capital costs. The steam/hot water may not be clean or it can contain tiny parts of the tube. These tiny parts, during the course of time, can block tubes, especially in narrow tubes. This method usually used when it is considered beforehand.

In summary:

Pros:

1.  Economical
2. Higher availability
3. Independence of electricity

Cons:

1.  Higher corrosion rates
2. Higher initial costs
3. Blockage risk
4. Shall be considered before manufacturing

Electricity:

In this method, a heating element is attached pipe/Equipment. This method is much easier to install and can be implemented whenever and wherever it is required. There is no risk of corrosion or blockage in this method. On the other hand, Electricity costs money and there is no “waste electricity”; thus this method is more expensive than using steam. It is obvious this method fails during power cuts.

In summary:

Pros:

1. Easier to Install
2. No need to foresee in basic design
3. No risk of corrosion
4. No risk of blockage
5. Lower Pipe/equipment capital cost (However, Electrical tracing cable costs more than steam tubes)

Cons:

1. Expensive to use
2. Cannot be used during a power shortage.

As mentioned above, each method has its pros and cons. According to our experience, we usually use steam tracing since there is lots of LP steam that cannot be used in any other process.

Case study:

For urea transfer after its production, we use a centrifugal API 610 pump. As the temperature falls below 140°C, Urea solidification begins. This type of pump requires heat tracing. The manufacturer uses steam tracing around as well as inside the casing and also in mechanical seals. As shown in figure 1, the pedestal of this pump needs cooling while the pump itself needs steam tracing to avoid solidification of melted Urea.

Figure 1- Courtesy of EBARA

Reference:

• Cover Picture: Thorne and Derrick heat tracing solutions
• Figure 1: Ebara pumps

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