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I am teacher in marine engineering subjects in an educational institute in Calcutta, India. A question was asked in examination concerning shell and tube heat exchangers on merits / demerits of the following methods of attaching cooler tubes to tube plates:

 rolling
 brazing
 use of packing and ferrules
 sweating ( I believe the correct term should be “swaging”)


Can any one please help me with the answers? A brief answer on each of the 4 methods will be sufficient.


Many thanks and best wishes

Ritinkar Sen

[Art Montemayor]

Ritinkar Sen:

There is one more popular method of joining a heat exchanger tube to its corresponding tubesheet that you haven’t mentioned. The methods are as follows:

1) Seal welding;
2) Mechanical rolling;
3) Brazing and sweating; and,
4) Packing, ferrules, or “O” rings.

By far the most-used method today in the processing industry is seal welding - used with carbon steel and stainless steel construction. Sometimes tubes are seal welded and then also rolled. Seal welding ensures that there will be no fluid leaks from one side of the exchanger to the other. In the past mechanical rolling was used more than it is today. Rolling gives the advantage of replacing the tube and re-using the same tube sheet. Today there are machining techniques that allow the same thing when confronted with seal welded tubes.

Brazing and sweating fall into the same category in that no electric arc welding is used; rather, an oxy-acetylene torch is used to administer a bronze weld or a lead/silver amalgam solder at relatively lower temperatures to the tube edges and seal them that way. This technique requires that the tube sheet be made of a material that will take the brazing or solder – such as copper or brass/bronze. Brazing and sweating methods require that the ultimate process temperature be below that where the bronze/lead seal does not fail. That’s why this method is used in processes close to ambient temperature or in the cryogenic zone. Lead/silver soldering is used a lot in cryogenic processes and some heat exchangers. The softer metals – like silver, lead, and copper – actually increase their tensile strength as the temperature gets colder.

Packing and ferrules are used in heat exchangers that operate at relatively very low pressures and where the possibility of leakage does not present a hazard.

When dealing with a solder, the correct term is “sweating”; swaging is a mechanical term and does not apply. I have never seen a swage applied to a tube-tube sheet joint.

I hope this helps.

Ritinkar Sen:

There is one more popular method of joining a heat exchanger tube to its corresponding tubesheet that you haven’t mentioned. The methods are as follows:

1) Seal welding;
2) Mechanical rolling;
3) Brazing and sweating; and,
4) Packing, ferrules, or “O” rings.

By far the most-used method today in the processing industry is seal welding - used with carbon steel and stainless steel construction. Sometimes tubes are seal welded and then also rolled. Seal welding ensures that there will be no fluid leaks from one side of the exchanger to the other. In the past mechanical rolling was used more than it is today. Rolling gives the advantage of replacing the tube and re-using the same tube sheet. Today there are machining techniques that allow the same thing when confronted with seal welded tubes.

Brazing and sweating fall into the same category in that no electric arc welding is used; rather, an oxy-acetylene torch is used to administer a bronze weld or a lead/silver amalgam solder at relatively lower temperatures to the tube edges and seal them that way. This technique requires that the tube sheet be made of a material that will take the brazing or solder – such as copper or brass/bronze. Brazing and sweating methods require that the ultimate process temperature be below that where the bronze/lead seal does not fail. That’s why this method is used in processes close to ambient temperature or in the cryogenic zone. Lead/silver soldering is used a lot in cryogenic processes and some heat exchangers. The softer metals – like silver, lead, and copper – actually increase their tensile strength as the temperature gets colder.

Packing and ferrules are used in heat exchangers that operate at relatively very low pressures and where the possibility of leakage does not present a hazard.

When dealing with a solder, the correct term is “sweating”; swaging is a mechanical term and does not apply. I have never seen a swage applied to a tube-tube sheet joint.

I hope this helps.

Many thanks. The information will be of great help.

Best wishes

Ritinkar Sen