Part I: Focus on the tube or pipe mill
March 22, 2006
If you're making flawed tube or pipe, don't blame the material. You need to start by examining every aspect of the mill. Only after verifying that the mill is in good working order can you turn your attention to the raw material.
In the beginning was the coil and all was well. The coil was large and heavy and not very useful, except as a big doorstop, so it was unwound, and then all was not well. Now it was a tripping hazard, and though impressive to behold, it still served no purpose. Ultimately, all things were put under man’s control, so man thought, I can make tube from the coil—after all, I have the fire-breathing dragon as a friend. Now as long as coil came from heaven all was well, but when the apple fell from the tree, things started to go wrong. Coil came from many locations, and because languages had become confused, no one understood the other. Shipments were missed, grades and gauges were inconsistent, and the coil became more like the snake that had started the problem in the first place.
Material-related problems have been around a long time. Maybe not since Adam and Eve left the Garden of Eden, but a long time nonetheless. To add to the confusion, the industry has many more types and grades of material than before, so if you make tube for a living, your life is interesting, to say the least.
To confront material problems, you must have hard information and know how to separate fact from fiction. No one will let you off easily; you may cite material problems as a reason for failure only when you can prove they exist. You can separate material problems into two groups: the ones within your control and the ones beyond your control.
To distinguish one from the other, you must first think about how a tube mill works. To prove that a material problem exists, you must know and document the capabilities of your mill and tooling. This way you will know when the material is the culprit. The basic rules that control the process are:
Now that you have followed all the rules and documented the process, the next step is to determine whether the tube is acceptable. To do this, you need to verify two of the mill’s capabilities: its ability to form the tube sufficiently to achieve a sound weld, and its ability to hold acceptable tolerances (diameter, shape, ovality, straightness). You should use destructive tests and continuous nondestructive tests (NDTs) to prove these capabilities.
Material problems can interfere with these two capabilities. Unless you manage the components within your control, you will be suspect when things go wrong. It must be clear that only one variable, material, is creating the problem.