What CuZn20Al2 / CW509L Aluminum Brass Tube Is
CuZn20Al2 is a wrought aluminum brass: a copper-zinc alloy with roughly 2% aluminum added. The same material is catalogued as C68700 in the UNS system, HAL77-2 in GB/T 8890, C6870 in JIS H3300, CZ110 in BS 2871 and CuZn20Al2 in DIN 1785, while CW509L is the designation carried for wrought hollow products in the European numbering referenced by DIN EN 12168. Seamless tubes in this grade are produced to DIN 17660, and for export markets the chemistry and mechanical requirements are frequently ordered to ASTM B111 as well.
The aluminum addition is what makes the grade useful. In service the tube surface develops a thin, tightly adherent aluminum oxide film that blocks chloride attack, so resistance to seawater impingement and to dezincification is markedly better than that of plain 65/35 or 70/30 brass. Copper ions released at the wetted surface also suppress biofouling to a practical degree in once-through cooling water. Thermal conductivity stays high for a copper alloy, which is why the grade dominates seawater-cooled condensers and heat exchangers.
Chemical Composition
| Element | Composition, % |
|---|---|
| Cu, including Ag | 76.0 - 79.0 |
| Al | 1.8 - 2.5 |
| Mn | 0.02 - 0.06 |
| Fe | 0.06 max |
| Pb | 0.07 max |
| Sn | Not specified |
| Ni, including Co | Not specified |
| Zn | Remainder |
These are the DIN 17660 limits for CuZn20Al2 and they correspond to the C68700 requirements of ASTM B111. Iron and lead are the impurities that matter most: excessive iron lowers corrosion resistance and can cause localised attack, while lead is restricted because it is insoluble in the matrix and forms discrete particles. The narrow manganese window is deliberate and is normally balanced against the aluminum content to keep the oxide film stable in flowing seawater.
Mechanical and Physical Characteristics
Strength: aluminum is an effective solid-solution strengthener, so tensile and yield strength sit well above ordinary brass of comparable zinc content and approach those of some low-alloy steels. Tubes therefore tolerate higher internal pressure and mechanical load at a given wall thickness.
Seawater corrosion resistance: the dominant design property. The grade resists impingement attack, erosion corrosion and chloride pitting in brackish water, estuarine water and chloride-bearing process streams.
Thermal conductivity: high enough for efficient heat transfer, which keeps the required surface area and tube count competitive against other copper alloys.
Formability: tube can be cold drawn, bent, coiled and roller-expanded into tubesheets in the annealed temper.
Joining: soldering and brazing behave predictably, but fusion welding of aluminum brass is more demanding than plain brass because the aluminum-rich oxide film is refractory and must be removed mechanically, then protected with an appropriate shielding gas. TIG welding with matching filler is normally used where welded joints are unavoidable.
Anti-biofouling: copper ion release limits slime and shell growth inside the tube, reducing cleaning frequency in seawater service.
Typical Applications
Condenser tubes for steam turbine plant in coastal power stations and for marine engines.
Heat exchanger tubes on ships, offshore platforms and desalination trains, where seawater or brackish water is the cooling medium.
Seawater piping, valve bodies and pump connecting lines requiring both strength and chloride resistance.
Geothermal heat exchange circuits, where the fluid is aggressive and hot.
Chemical heat exchangers handling acid, alkali and salt solutions, and high-pressure hydraulic lines that need toughness plus moderate corrosion resistance.
Selection and Fabrication Guidance
Temper selection drives the whole fabrication route. Annealed tube is chosen when the tube is to be roller-expanded into a tubesheet or bent to a tight radius, because the low yield strength lets the wall deform without cracking. As-drawn temper is preferred for straight runs carrying higher pressure, where stiffness and dimensional stability matter more than formability.
Order the tube by outside diameter, wall thickness, length, standard, temper and test requirement, and state whether the tubes are intended for expansion, welding or brazing. Weld zone properties, residual carbon film inside the bore and dimensional ovality are the three areas where heat exchanger performance is most often lost, so specify them explicitly rather than relying on the default scope of the standard.
Inspection Points
Chemical verification of copper, aluminum and manganese against the ordered grade, since the aluminum content controls the corrosion performance.
Hydrostatic or pneumatic pressure test where leak tightness is critical, with eddy-current testing of the finished tube to detect wall defects.
Outer diameter, wall thickness, eccentricity and roundness, all measured at several positions along the length.
Surface condition: freedom from laps, seams, rolled-in scale, drawing marks and residual carbon; bore cleanliness is essential before assembly.
Temper verification by hardness or tensile test, and full documentation of heat number traceability.
FAQ
Q: Why is CuZn20Al2 preferred over plain brass for seawater condensers?
The aluminum addition forms a dense, adherent oxide film on the wetted surface, which suppresses impingement attack and dezincification. Plain brass of the 65/35 or 70/30 type corrodes much faster in flowing seawater and is normally restricted to fresh water and low-chloride duty.
Q: What does the CW509L designation mean?
CW509L is the code used for wrought copper-alloy hollow products in the European numbering system referenced by DIN EN 12168. The chemistry and mechanical requirements that govern the tube itself are those of the aluminum brass grade CuZn20Al2 as specified in DIN 17660 and, in ASTM terms, as C68700 in ASTM B111.
Q: Which equivalent grades can be offered instead?
The grade is interchangeable across systems: C68700 in UNS, HAL77-2 in GB/T 8890, C6870 in JIS H3300, CZ110 in BS 2871 and CuZn20Al2 in DIN 1785. Confirm the standard and temper you want to order against so that dimensional tolerances match your tubesheet practice.
Q: Can CuZn20Al2 tube be welded?
Yes, but fusion welding is considerably less forgiving than with plain brass because the refractory aluminum oxide film must be removed and excluded during the pass. TIG welding with matching filler and full gas coverage is the usual route; brazing or soldering is preferred whenever the joint design allows it.
Q: What tube temper should be ordered for roller expansion into a tubesheet?
Annealed tube. The low yield strength in the annealed condition lets the wall expand into the tube hole and groove without cracking, giving reliable contact for heat transfer. Hard-drawn tube is used for straight, high-pressure runs where expansion is not required.
Q: How is the tube protected during shipping and storage?
Tubes are supplied dry, with the bore free of drawing lubricant and carbon residue, ends protected against mechanical damage and the bundles wrapped against moisture. Copper alloys tarnish and can suffer ammonia-induced stress corrosion cracking, so keep the material away from ammonia, amine-bearing atmospheres and humid industrial air.
