Which is more important, Weld Integrity, or Welded Tube Size?

A trick question? Not really, as a point is needed to be made here concerning these two topics, Weld Integrity, and Welded Tube Size.

The correct answer is, "BOTH".

• Everyone knows that we need good weld integrity so that the end product will survive and meet quality standards in its final application or fabrication requirements.
• However, some would answer the above question in the following manner: "Weld integrity is all that matters! If I have to squeeze (adjust the weld roll pressure) in on the weld box, and turn up the heat (power from the welder) to get a good weld, that is fine! And if the welded tube size is smaller than the dimensions on the set up chart that is also fine, that way the sizing section does not have as much work to do". "INCORRECT"
• We must have proper welded tube size in order to properly size/stress relieve the tube/pipe in the sizing section.
• We also must insure we have a "round" welded tube size, which is the way most weld roll tooling is designed. All too often, operators measure the OSP (Girth) with a pie/diameter tape, and if it matches close to the welded O.D. from the set up chart, they call it good. However, a pie/diameter tape does not tell you the ovality of the welded tube/pipe. This is why it is necessary to measure this with a micrometer to insure we are sending the proper sized (and shape) of welded tube/pipe to the sizing section, not a high or flat oval which can adversely affect the final sizing of the tube/pipe.
• Common sense will tell us that in order to have a successful welded tube/pipe; we must first insure we have set up the breakdown and fin sections properly, as per our previous Profit Pointer topics. (See our technical articles: "Setting Up The Breakdown Section" and "Setting Up The Fin Section".

Also, insure the strips edges are in good condition.

• There is a wide variety of types of materials (ferrous and nonferrous) produced on tube/pipe mills. With that we find a wide host of "types" of welding to match the product line mix, be it ERW (Electric Resistance Welding), HF (High Frequency—both coil and contact), TIG, MIG, LASER and PLASMA, just to name a few. It is imperative the tooling design matches the type of material and type of welding as well as the strip width for the same. Consult with your tooling supplier if you are unsure of any of these issues.

Most firms conduct at least a basic mechanical test to insure weld integrity.

Others may cut and polish a welded sample and check the weld under a microscope to insure the flow lines and bond is proper and/or add other additional tests such as a tensile pull test.

To follow are some causes and solutions for poor weld integrity.

Look for continued articles to follow on the proper set up of the sizing section here on Roll-Kraft's web site, which offers the most comprehensive, informative and interactive technical information in the industry.

Written by: Robert A. Sladky, Vice President Tube Mill Engineering