There are multiple options available for securing a leak-free and reliable connection between the tube and tubesheet. The tube-tubesheet joint is a true metal to metal seal obtained by expanding the tubes into the tubesheet. When the mechanical forces are removed, the tubes are subject to residual compressive stress and tubesheet has residual tensile stress, with the wall reduction being the amount of plastic strain in the tubes. As the joint is subjected to repeated stress cycles/thermal cycles, the residual stress has a tendency to relax, which may lead to leakage, which can easily be remedied by employing a seal or strength weld. Ohmstede Ltd. provides the option of mechanical and/or hydraulic tube expansion, with the vast majority utilizing the mechanical expansion method.
Ohmstede Ltd. offers both tapered and/or parallel roller pin tube expansion, depending on the application or client preference. We offer both standard and customized tooling, allowing expansion of the tube into any thickness of tubesheet.
Hydraulic expansion (HydroSwage®) is the direct application of hydraulic pressure to permanently expand a tube to form a leak-proof joint between the tube and tubesheet. This methodology is ideal to seal the tubes uniformly through the entire thickness of the tubesheet. Hydroswage® accomplishes this by filling the tube inside area, within the thickness of the tubesheet, with a fluid and controlling the pressure to yield the tube material, staying below the yield of the tubesheet.
Ohmstede Ltd. offers two types of tube-tubesheet welds. We offer a one pass weld (Seal Weld) and we offer a two-pass weld (Strength Weld). These two types of welds can be utilized, with either of the expansion methods mentioned above, to achieve the following: