Shell and tube heat exchangers built to API 660 and TEMA are used across refining, petrochemical and natural gas processing plants for heating, cooling, condensing and reboiling process fluids.
The unit consists of a shell, tube bundle, tubesheets, baffles and channel. Tube-side fluid passes through the tubes; shell-side fluid crosses the bundle under baffle guidance. Heat transfers through the tube wall from the hotter stream to the colder one.
A note on standards: API 660 covers shell and tube heat exchangers, while API 661 applies to air-cooled heat exchangers. The two differ in heat transfer mechanism, construction and selection inputs, and are not interchangeable. Specify the equipment type before fixing the standard edition in an inquiry.
Three configurations cover most process duties, identified by the TEMA rear-head designation:
TEMA class directly affects tubesheet thickness, minimum shell thickness and nondestructive examination coverage. Class R applies to severe refinery service, Class C to general commercial service, Class B to chemical process service.
| Standard | Scope | Notes |
|---|---|---|
| API 660 | Shell and tube exchangers for petroleum, petrochemical and natural gas service | Edition per project specification (9th / 10th); adds requirements on tube-to-tubesheet joints, tubesheet calculation and inspection |
| TEMA | Construction type and minimum wall thickness | Class R / C / B |
| ASME BPVC Section VIII Div. 1 | Design by rule and fabrication | U stamp available |
| GB/T 151 | Domestic Chinese projects | Where applied alongside ASME, the contract governs precedence |
| PED 2014/68/EU | Export to the European Union | CE marking and notified body involvement required |
| NACE MR0175 / ISO 15156 | Wet H2S service | Limits material hardness and heat treatment condition |
| Parameter | Range |
|---|---|
| Shell nominal diameter | DN150 – DN2000 |
| Tube size | Ø19 × 2 mm, Ø25 × 2.5 mm |
| Tube length | 1500 – 9000 mm |
| Tube-side design pressure | Full vacuum – 10 MPa |
| Shell-side design pressure | Full vacuum – 6.4 MPa |
| Design temperature | -40 – 450 °C (carbon steel) |
| Heat transfer area, per unit | 1 – 2000 m² |
The table describes normal fabrication capability, not the fixed specification of any single model. Final values follow from the process package, the strength calculation and the pressure drop check. Range endpoints should not be quoted directly as selection values.
Shell and channel. Carbon steel to SA516 Gr.70 or Q345R. Corrosive service calls for SA240 304/316L; chloride-bearing streams for duplex S31803; seawater and aggressive media for titanium Gr.2.
Tubes. Seamless tube to SA179 / SA192, welded tube to SA249, stainless to SA213 TP316L. Tube diameter and wall thickness must satisfy heat transfer area and corrosion allowance together — neither can be fixed independently.
Tubesheets. Forgings to SA266 Gr.2 for carbon steel construction or SA182 F316L for stainless, with thickness taken as the greater of the TEMA and ASME results.
Tube-to-tubesheet joints. API 660 sets explicit requirements here. The standard practice is strength expansion plus seal welding. Thin-wall or titanium tubes are hydraulically expanded to avoid the work hardening that mechanical rolling introduces. Welding procedures are qualified to ASME Section IX.
Welding and heat treatment. Longitudinal and circumferential seams receive RT or UT as the project specifies. Carbon steel units above the specified thickness receive post-weld heat treatment.
Without every item above, heat transfer area and construction type cannot be determined uniquely. Supplying the process datasheet with the inquiry removes most of the back-and-forth.
A removable bundle allows mechanical cleaning and suits services with a clear fouling tendency. Fixed tubesheet units permit cleaning on the shell side only; tube-side fouling requires chemical cleaning. Floating head and U-tube designs need maintenance clearance reserved at the civil design stage, not after installation.
