Titanium has features of small density, high specific strength, corrosion-resistance, high elasticity, low damp, zero magnetism and good property at high/low temperatures. It is praised as spacial metal and marine metal and is widely applied in the fields of national economy and national defense construction, such as aerospace, sea water desalination, watercraft, chemical engineering, vehicles and electric power. Seamless pipes have low rate of finished products, long production cycle and high cost, while soldered pure titanium pipes have short production process, low production cost and high production efficiency. Therefore, it is a tendency for pipe production to develop thin-wall soldered pipes. In Japan and European countries, soldered titanium pipes are gradually replacing thin-wall titanium and titanium alloy seamless pipes. They are applied in condensers in coastal power station and nuclear power station, which not only improves rate of heat exchange, but also improves lifespan of condenser units, leading to significant economic benefit.

 When titanium pipes are soldered, it should guarantee that

 (1) In soldering area, at temperature of over 250℃, metal is not contaminated by active gases and harmful impurity elements, including N, O and H, C, Fe and Mn.

 (2) Coarse grain structure could not be formed.

 (3) No large soldering residual stress and residual deformation. Therefore, during soldering process, predetermined construction sequence should be followed, and whole-process quality control should be conducted via strictly following process quality control standard. People, machine, material and method are under good control, to ensure soldering quality of titanium pipes during reasonable time limit.

Burst pressure of soldered titanium pipes is 61.76MPa. When tiny crack appears at longitudinal seam, water in pipes rushes out from soldering seam. Burst pressure of seamless titanium pipes is 68.10MPa. When large crack appears at the joint between plugs and pipes, water in pipes rushes out from the joint, and the seamless pipe itself is not damaged. Vibration of titanium pipe heat exchanger and condenser during use induced by shell pass fluid results in different fluid's vortex, buffet, elastic shock excitation and acoustic resonance. Combination of such vibration forms dramatic vibration, thus causing pipes to continually hit the baffle plate and then generating phenomena that pipes are cut and penetrated by edges of the baffle plate, and joint between pipes and pipe sheets is split to cause leakage. Therefore, soldered titanium pipes and seamless titanium pipes go through the vibration fatigue test to count fatigue times respectively under equal condition, to determine if soldered titanium pipes as replacement of seamless titanium pipes has influence on equipment’s lifespan.

 (1) Expanded joint of soldered titanium pipes: under equal pressure of expanded joint, soldered titanium pipes’ pulling-out force is 2.5-3.1MPa larger than seamless titanium pipes. After expanded connection, soldered titanium pipes are bonded with fixtures more closely and sealability of expanded connection is better.

(2) Within defining range of pressure vessels, soldered titanium pipes could bear design pressure up to 35MPa and maintain pressure for 3 minutes without leakage.

(3) Frequency of soldered titanium pipes and seamless titanium pipes is 30. 

Principles and technique of tensioning by the roller is same as seamless titanium pipes. But existence of beads requires considering addition factors, in order to determine the best and the most stable technique of tensioning by the roller. Among these factors, the most important are metallurgy quality and surface status of pipes. For example, for pipes in annealed condition instead of soldered condition, over projecting compensating beads has to be avoided for connection of pipe sheets.  It is proved that air-annealed head, with flared tube and polished loop, has better bonding strength than pipes after enlargement in condition of bright annealing or bright stress relieving annealing.

On the other hand, coarse surface of pipes or pipe sheets could improve mechanical strength, but its sealability is poor. Manufactured by precision machining or precision machining plus remorninging, titanium pipe sheets’ hole has surface smoothness of 0.75-1.5-101. At the pipe head, smoothness of polished loop reaches the same level. So combination of strength and sealability is optimal.