TEMA/ASME Hairpin Heat Exchanger
The hairpin heat exchanger is a shell-and-tube type configuration consisting of a U-shaped tube bundle enclosed within a shell that includes a return bend housing at one end. The shell-side fluid enters at the front head, flows along the straight leg to the return bend, reverses direction, and exits at the front head. The tube-side fluid enters through the front tubesheet, passes through the U-tubes, and returns through the same tubesheet. This arrangement produces a single-pass countercurrent flow between tube-side and shell-side fluids.
This product is designed and manufactured in accordance with TEMA (Class C, B, or R) and ASME Section VIII Division 1 or Division 2, with applicable materials selected per ASME Section II.
Construction Types
Double Pipe Hairpin (Single Tube)
- Tube: Single seamless or welded pipe (OD 20mm to 114mm), concentric within a larger shell pipe
- Shell: Single pipe (DN50 to DN200) serving as the outer pressure boundary
- Application: Small duty areas (1 to 20 m²), high-pressure services (tube side up to 35 MPa), clean fluids on both sides
- Inspection: Full access to internal tube surface from front tubesheet; shell side can be inspected via removable return bend cover
Multitube Hairpin (Multiple Tubes in Shell)
- Tube bundle: Multiple tubes (4 to 200+) arranged in triangular or square pitch within a cylindrical shell
- Shell: DN80 to DN600, with a return bend housing at the far end
- Application: Medium to large duties (20 to 500 m²), moderate pressure (shell side up to 10 MPa, tube side up to 20 MPa)
- Tube support: Baffle plates or full support grids per TEMA RCB-4.2 (maximum unsupported tube length: for carbon steel ≤ 36* tube OD; for stainless steel ≤ 30* tube OD)
Geometric Parameters (Standard Range)
| Parameter |
Double Pipe Type |
Multitube Type |
| Shell nominal diameter (DN) |
DN50 to DN200 |
DN80 to DN600 |
| Tube OD |
20mm to 114mm |
12mm to 38mm |
| Tube wall thickness |
2.0mm to 8.0mm (seamless) |
1.5mm to 3.0mm (seamless or welded) |
| Straight leg length (per leg) |
2.0m to 10.0m |
2.0m to 12.0m |
| U-bend radius (centerline) |
R ≥ 2* tube OD (min. for cleaning) |
R ≥ 2* tube OD |
| Number of tubes per bundle |
1 |
4 to 200+ |
| TEMA shell type |
N/A (double pipe) |
Hairpin (return bend shell) |
Material Selection (Per Service Conditions)
Tube Material Options
- Carbon steel (SA-106 Gr.B / SA-210 Gr.A1 / 20#): Water, oil, non-corrosive gases; temperature -20°C to +425°C
- Stainless steel 304/304L (SA-213 TP304L): Mildly corrosive process fluids, clean steam; chloride ≤ 200ppm; temperature -196°C to +600°C (derated above 425°C per ASME II-D)
- Stainless steel 316/316L (SA-213 TP316L): Organic acids, salt solutions (chloride ≤ 200ppm for 316L); temperature -196°C to +500°C
- Titanium Gr.2 (SB-338): Seawater, brine, chloride solutions up to 20,000ppm; temperature ≤ 230°C
- Duplex 2205 (SA-789 UNS S32205): Chloride-containing hydrocarbons, seawater; chloride up to 300ppm at 80°C; temperature -40°C to +280°C
Shell Material Options
- Carbon steel (SA-516 Gr.70): Non-corrosive or mild corrosive on shell side; design temperature -20°C to +425°C
- Stainless steel 304L / 316L: Shell-side corrosive media or high-purity requirement
- Titanium (for seawater shell side, where shell-side fluid is seawater)
Gasket Materials (per temperature range)
- Non-asbestos / compressed fiber: -40°C to +250°C, pressure ≤ 4.0 MPa
- Spiral wound (SS 304/316 + graphite): -196°C to +450°C, pressure ≤ 25 MPa (double pipe flange)
- PTFE envelope gasket: -40°C to +200°C, for pharmaceutical or corrosive services where contamination is restricted
Operating Range (Non-Exaggerated)
| Parameter |
Double Pipe Type |
Multitube Type |
| Design pressure (tube side) |
Up to 35 MPa (ASME VIII-2) |
Up to 20 MPa |
| Design pressure (shell side) |
Up to 10 MPa |
Up to 10 MPa (standard); higher per special design |
| Design temperature (tube side) |
-40°C to +500°C (material dependent) |
-196°C to +500°C (material dependent) |
| Design temperature (shell side) |
-40°C to +450°C (material dependent) |
-40°C to +450°C (material dependent) |
| Minimum allowable ΔT (tube/shell inlet) |
No fixed limit (U-bundle free end) |
No fixed limit (U-bundle free end) |
| Maximum tube-side velocity (water) |
3.0 m/s (carbon steel), 4.5 m/s (titanium) |
2.5 m/s (carbon steel), 4.0 m/s (titanium) |
| Maximum shell-side velocity |
1.5 m/s (corrosive), 3.0 m/s (clean) |
1.0 m/s (corrosive), 2.5 m/s (clean) |
Flow and Thermal Design Parameters
Tube-side flow
- Single pass (all tubes share same inlet and outlet at front tubesheet)
- Tube-side mass velocity range: 300 to 2,500 kg/m²*s (for water); lower for viscous fluids
- Reynolds number target: ≥ 10,000 (turbulent) for clean service; ≥ 4,000 for viscous fluids
Shell-side flow
- Single pass (enters front head, traverses straight leg, reverses at return bend, traverses second leg, exits front head)
- Shell-side mass velocity range: 50 to 500 kg/m²*s (gas), 200 to 1,500 kg/m²*s (liquid)
- Baffle cut percentage (segmental baffles, if used): 20% to 30% of shell diameter
- Baffle spacing: Determined per TEMA RCB-4.2 - maximum unsupported tube length not to exceed 36* tube OD for carbon steel; spacing selected to maintain cross-flow velocity and prevent tube vibration. Typical spacing range: 0.2* shell ID to 0.5* shell ID.
LMTD correction factor
For true countercurrent single-pass configuration, F = 1.0 per TEMA standards (no temperature cross limitation).
Approach temperature
Minimum practical approach: 3°C to 5°C (limited by available surface area and NTU; actual achievable value depends on specified pressure drop and fluid properties, not guaranteed without process simulation).
Fabrication and Welding Parameters
Tube-to-Tubesheet Joint
- Expanded joint: Hydraulic expansion at 160-220 MPa, hold 5-8 seconds. Pull-out test requirement (per TEMA RCB-4.3): ≥ 20 MPa for carbon steel tubes; ≥ 25 MPa for stainless steel.
- Welded joint: Seal weld (fillet leg 1.5-2.0mm) plus full penetration (for toxic/high-pressure service). Weld procedure qualified per ASME Section IX.
- Combined (weld + expand): Used for cyclic temperature service (thermal cycle > 100 cycles) and high-pressure (tube side > 10 MPa).
Return Bend Housing Weld
- Shell return bend cap: Full penetration butt weld (if permanent cap) or bolted cover with spiral wound gasket (if removable).
- Internal welds: 100% visual inspection (VT) + penetrant testing (PT) on critical fillet welds (per ASME VIII-1 UW-50).
Post-Weld Heat Treatment (PWHT)
Required per ASME VIII-1 UCS-56 when:
- Carbon steel shell thickness > 38mm (P-No.1, group 1/2) for welded pressure parts
- Tube material thickness > 19mm (for stainless steel, solution anneal after welding is specified instead of PWHT)
- Service contains wet H₂S (per NACE MR0175 / ISO 15156) - PWHT at 620±10°C for 1 hour per 25mm of thickness, minimum 1 hour.
Inspection and Testing (Per Unit)
Dimensional Check
- Overall leg length tolerance: ±3mm (for straight legs) per TEMA RCB-8
- U-bend centerline radius tolerance: ±1.5mm for R ≤ 500mm; ±3mm for R > 500mm
- Baffle / support plate spacing: ±1.5mm
- Tube hole ligament (web) deviation: ≤ ±0.2mm from drawing
Non-Destructive Examination
- Tube-to-tubesheet joints: 100% liquid penetrant (PT) for seal welds (per ASME VIII-1 UW-51)
- Shell longitudinal and circumferential seams: Spot radiography (RT) per ASME VIII-1 UW-52 (or full radiography if specified)
- Return bend housing fillet welds: 100% magnetic particle (MT) for carbon steel / PT for stainless steel
- Tube internal inspection: Borescope verification of straightness and pass-through (no blocked tubes) - passed if 100% of tubes accept a gauge ball 0.5mm smaller than tube ID.
Pressure Testing
- Hydrostatic test (water): Test pressure = 1.3 * design pressure * (minimum allowable stress at test temperature / at design temperature), per ASME VIII-1 UG-99. Hold 30 minutes. Acceptance: no visible leakage and no pressure drop.
- Pneumatic test (optional, for dry or gas service): Test pressure = 1.1 * design pressure. Compressed air or nitrogen. Soap bubble check on all joints. Leakage rate not to exceed 1*10⁻⁵ Pa*m³/s per equivalent orifice method (per ASME Appendix VI).
Cleaning and Maintenance Access
Tube-side cleaning
- Mechanical cleaning: Tube wiper or brush passes through full tube length via U-bend. Minimum U-bend radius R ≥ 2* tube OD required per TEMA RCB-4.52 for brush passage. Standard brushes of OD 0.8* tube ID are recommended.
Shell-side cleaning
- Chemical cleaning only for fixed bundle hairpin (return bend cover removable but bundle not pullable). Shell-side mechanical cleaning via access ports is limited to the straight leg sections; return bend interior not accessible by mechanical scrapers.
- If shell-side fouling factor > 0.0005 m²*K/W (per TEMA table), a pull-through floating head or U-tube straight-shell exchanger is recommended instead of hairpin. For hairpin, chemical cleaning cycle frequency based on pressure drop increase: clean when shell-side ΔP exceeds design ΔP by 30% or when ΔP increase reaches 50 kPa (whichever occurs first).
Documentation Provided per Shipment
- ASME U-stamp data report (if applicable)
- Material test certificates (EN 10204 3.1 or 3.2)
- Welding procedure specification (WPS) and procedure qualification record (PQR)
- Pressure test report with chart recording
- Dimensional inspection report
- Tube bundle drawing (as-built)
- NDE report (PT/MT/RT/UT as applicable)
Design Limit Statement
The hairpin exchanger is not applicable for:
- Shell-side fluids with solids content > 5% by weight, or fibrous fouling that requires mechanical bundle extraction for cleaning - because the hairpin bundle is fixed and cannot be pulled through the return bend housing.
- Shell-side mass flow rates exceeding the equivalent of 500 kg/s through DN600 shell - due to single shell pass causing pressure drop exceeding the typical 50-80 kPa design limit (per TEMA allowable pressure drop guideline).
- Very high shell-side vacuum service (< 1 kPa absolute) - the return bend housing may require additional stiffening rings per ASME VIII-1 UG-29 to prevent collapse under external pressure; consult design.
Sizing Input Required for Quotation
To provide a preliminary thermal and mechanical design, submit the following process data:
- Tube-side fluid name and composition (if mixture)
- Shell-side fluid name and composition
- Tube-side inlet / outlet temperatures
- Shell-side inlet / outlet temperatures
- Tube-side allowable pressure drop
- Shell-side allowable pressure drop
- Tube-side operating pressure
- Shell-side operating pressure
- Maximum available footprint (straight leg length, headroom)
- Fouling factors (tube side and shell side), if known; otherwise standard TEMA values will be applied
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