May 15, 2019
Even when a fabrication service has access to the finest manufacturing facilities, it's not possible to manufacture a high-performance pressure vessel if it's not equipped with an alloy-strengthened material backbone. Stretching that metaphor just a little further, the materials require flexibility, again, just like a backbone. To put it another way, the fluid containment alloy has to be ductile so that the vessel walls can expand and contract.
Expandable Alloy Walls
Furnished with high-tensile strength, a heat treated carbon steel delivers optimized material hardness. The microcrystalline structure should be free of impurities and not overly carbon-rich. Otherwise, by using high carbon steel, brittleness issues will ensue. Ideally, ductile low-to-medium carbon steels are better at containing high-pressure fluids. Because of this feature, thin-walled pressure vessels provide corrosion resistant, shock dampened strength, which means lower production costs all around. Then, with fluid pressures on the rise, a ductile carbon steel envelope will expand until the system stresses equalize.
Applying the Stainless Steel Advantage
Just like carbon strengthened alloys, stainless steel comes to the fabrication shop bending machines as thin-walled but high tensile strength sheets. The chromium and nickel reinforced metals in this popular alloy family are highly corrosion resistant. Whether the material threat exists because of a conventional oxidization attack or a complex chemical assault, stainless steel pressure vessels handle the onslaught. Carbon steels, on the other hand, will likely experience material fatigue when faced by such corrosive attacks. Moreover, there are scores of differently graded stainless steels, many of which are weldable and easy to machine.
Low and High-Pressure Substitutes
Aluminium can be used as a stainless steel substitute if the contained pressures aren't extremely high. Take note, however, certain aluminium-rich alloys are not easy to weld. Even if this issue is somehow overcome, there's always the possibility of a hydrogen solubility issue. This issue becomes even harder to manage if the equipment is intended for a hydrocarbons processing facility. Titanium is a more advantageous material, one that can function under the most hostile operational conditions. Of course, should the need arise, there are a number of super-alloys available. One such material is Inconel, which is an austenitic chromium-nickel metal that's built to handle great pressures and thermal extremes.
The question asked about the "Ideal Material." Well, all of the alloys covered above fit that description to some degree. Only, the super-alloys mentioned here can be prohibitively expensive. Even steel and aluminium can cause problems. For instance, one grade may be perfectly machinable but hard to weld. Really, for an ideal pressure vessel material, that alloy can only be chosen after the fluid properties and exterior environment have been assessed. Stainless steel occupies a selection sweet spot, but, should extreme conditions require it, there are the titanium alloy families and super-alloys, too.
Fusion - Weld Engineering Pty Ltd
ABN 98 068 987619
1865 Frankston Flinders Road,
Hastings, VIC 3915
Ph: (03) 5909 8218
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