There are a few things you can ask welders before you hire them to get an idea of their experience and ability levels:

• Are you licensed and certified?

• How long have you been in the welding business?

• Do you commonly do the type of welding I need?

• Do you offer any kind of warranty for your work?

• Do you charge by the hour or by the project?

• How long do you expect my welding project to take?

• What steps do you take to minimize errors in your work?

The best thing to cut metal pipe is a durable pipe cutter that is made for metal. You may want to measure the diameter of the pipes before purchasing a pipe cutter to ensure it will be able to cut your metal pipes. Opt for a heavy-duty option to cut through metal like steel or cast iron.

Welders use a variety of methods in their trade. Different types of welding are better suited for different purposes and contexts. For example, stick welding is a versatile form suitable for most metals and alloys. The most common types of welding include:

• Stick welding: $100–$1,000

• Metal Inert Gas (MIG) welding: $250 and up

• Tungsten Inert Gas (TIG) welding: $250 and up

• Gas welding: $150 and up

• Forge welding: $15–$25 per hour

Cutting rectangular ductwork requires careful measurements and the right technique. Use a measuring tape and pencil to mark the cutting lines accurately. Tin snips are excellent for straight cuts on smaller ducts. For more extensive or thicker rectangular ducts, a reciprocating saw with a metal-cutting blade is effective. 

Ensure the duct is well-supported and secure while cutting to prevent wobbling and maintain precision. After cutting, use a metal file to smooth any sharp edges, ensuring safety during installation.