Introduction
Heat exchangers represent a critical system within a refinery or petrochemical plant, where heat must be exchanged between fluids within a process. They are used for thermal processing, heating, cooling, condensation, and other functions which support around-the-clock plant operations. Factors influencing their performance include equipment design, operating conditions, fluid characteristics, and the materials selected for their construction.
Choosing the most suitable heat exchanger tubes for refineries is not an exercise in value-for-money buying alone. Material characteristics, dimensional compatibility, operating environment and applicable standards all impact on the suitability of the tube.
By understanding the factors involved in selecting suitable heat exchanger tubes for refinery and petrochemical heat exchangers, procurement professionals and engineers can develop their purchasing criteria in order to specify products correctly before the buying process commences.
1. Define Operating Conditions
The first step in choosing industrial heat exchanger tubes is to define the operating conditions. Process fluids in a refinery or petrochemical plant can vary greatly, and can include higher working temperatures or pressures, as well as suspended particulates or corrosive materials.
Prior to selecting an appropriate industrial heat exchanger tube, buyers should therefore identify:
- Operating and design temperatures.
- Operating and design pressures.
- Chemical composition of the process fluid.
- Potential for corrosion or erosion.
- Required thermal performance.
- Applicable codes and product standards.
- Operating and maintenance conditions anticipated.
This information will guide tube selection, influencing the material grade, the tube dimensions, the manufacturing process and the need for inspections.
Not all material grades can perform in the same application – even within the same environment for different exchanger designs. Always select the tube on the basis of the intended application.
2. Select the Appropriate Heat Exchanger Tube Material
The heat exchanger tube material can influence mechanical properties, thermal capability, and therefore suitability for a given application. The choice of material is dependent on the overall service requirements for the selected tube, not on a single characteristic.
Carbon Steel Tubes
Carbon steel tubular products are commonly selected for a range of industrial applications including heat exchangers, where the selected grade is suitable for the mechanical and dimensional capabilities in addition to the service conditions.
When considering carbon steels, buyers should be aware that operating temperature, pressure, fluid characteristics and any applicable design requirements should be met by the selected grade, which should be fit for purpose according to the relevant product specification.
Alloy Steel Tubes
Alloy steels consist of additional elements present within the steel, which contribute to mechanical characteristics such as strength, hardenability, creep resistance and other properties according to the alloy grade.
Certain grades of alloy steel are specified for applications where high temperature service is likely. However, not all grades are fit for all service conditions – the right grade of alloy steel should therefore be determined according to the applicable engineering specification.
Other Material Considerations
Some process environments require a higher level of protection, such as resistance to specific forms of corrosion. In these cases, careful consideration should be given to actual chemical environments, temperatures, and predicted potential for attack prior to finalising the material selection. Material selection should follow from the equipment design requirements and standards which apply to the equipment being fitted.
3. Specify Heat Exchanger Tube Specifications
Clearly defined heat exchanger tube specifications assist the manufacturer in delivering the correct product, as incomplete specification can lead to delays across the quotation, production, inspection, and delivery stages.
The purchase specification should therefore include:
- Material grade, and relevant standard.
- Outside diameter and thickness.
- Required tube length.
- Tolerances.
- Heat treatment condition.
- Surface condition and finish.
- Mechanical and chemical requirements.
- Testing and inspection requirements.
- Product marking and documentation.
Such information is particularly important in specifying replacement tubes – the replacement product must be capable of integration within the existing equipment design, and the specifications should be checked to determine whether previous dimensions and requirements still apply.
4. Define Seamless Tube Construction
Seamless tubes feature no weld along the length of the tube. They are utilised in industrial applications where seamless construction is specified by the equipment design or applicable standard.
However, the construction method on its own does not dictate pressure rating, overall resistance characteristics, or performance – the material grade, dimensions, manufacturing condition and design requirements are additional factors.
When buying seamless tubes, buyers should ensure they are aware of the manufacturing route, material grade, tolerances and testing requirements relevant to the selected product.
Once supplied, the product should conform to the relevant standard and purchase specification.
5. Define Dimensional Requirements
Defining dimensional requirements is important to ensure tubes are appropriately sized for the heat exchanger application in which they will be installed. Outside diameter, thickness, length, straightness, and other characteristics can have an influence.
Rather than simply utilising nominal dimensions, buyers should identify required tolerances – particularly when specifying replacement tubes where incorrect dimensions could interfere with installation or assembly within the equipment.
The manufacturer should be able to confirm suitability and capability of manufacture of the defined dimensions, and able to state any limitations which might apply specific to the material or manufacturing route.
6. Define Inspection and Testing Needs
Inspection and testing is necessary to ascertain product conformance to the agreed specification.
According to the product and applicable standard, requirements can vary and may include:
- Dimensional inspection.
- Chemical analysis.
- Mechanical testing.
- Hydrostatic testing (if applicable).
- Ultrasonic or eddy current testing (if applicable).
- Visual and surface inspection.
- Material identification and traceability.
Not all tests apply to all tubes – the inspection programme should always be defined according to the relevant standard, product requirements, and customer specification.
Buyers should also determine what inspection reports, test results, and certificates will accompany the order.
7. Define Long-Term Operating Requirements
The purchase price of a heat exchanger tube is only one consideration – buyers should also be aware of the service environment in which it will be placed and the impact this can have on its performance. In addition, maintenance requirements, access for inspection and the impact of unplanned downtime must also be considered.
An appropriately selected tube specification can reduce the risks associated with incorrect material selection, incorrect product dimensions, or inadequate documentation.
However, even a correctly specified tube requires appropriate manufacturing, installation, operation, and maintenance. The buying decision should therefore be part of a wider equipment reliability framework.
Heat Exchanger Tubes at Sainest
Sainest Tubes manufactures carbon steel and alloy seamless tubes for a range of industrial applications. Its product range includes heat exchanger tubes as well as U-bend tubes.
Buyers looking to purchase industrial heat exchanger tubes for refineries and petrochemical plants should state the intended application, material grade, dimensions, applicable standard, and testing requirements. This information can assist in determining whether a given product is appropriate for their application.
The capabilities of the manufacturing route and suitability for a given specification should be identified for each order.
Conclusion
Choosing the right tubes for refineries and petrochemical heat exchangers is a multi-step process. By identifying the right heat exchanger tube material, and defining heat exchanger tube specifications, buyers can ensure they choose the correct heat exchanger tube product for their equipment application.