Titanium and Copper-Nickel Construction

U-Tube Heat Exchangers For

Titanium and Copper-Nickel Construction
U-Tube Duty

Seawater defeats most alloys eventually. Titanium ignores it entirely. Copper-nickel handles it well within a velocity band that has to be respected in both directions.

Titanium Grade 2. Effectively immune to chloride attack including seawater, brine and hypochlorite, at any concentration and across the temperature range these exchangers see. It is thin-walled and light, so the cost per square foot is considerably less punishing than the price per pound implies.

Copper-nickel. 90/10 and 70/30 alloys have long been standard in seawater service, and they carry a genuine advantage in biofouling resistance because copper ions discourage marine growth. The constraint is velocity: too high and the protective film erodes away, too low and deposits form and cause under-deposit attack.

Velocity Is the Copper-Nickel Constraint. Copper-nickel relies on a protective surface film. Exceed the alloy's velocity limit and that film erodes faster than it reforms, producing erosion-corrosion that concentrates at tube inlets and at any local turbulence.

Run too slow and the opposite problem appears: deposits settle, and corrosion proceeds underneath them where the film cannot maintain itself. The result is a design window rather than a maximum, and it has to be checked against turndown as well as design flow.