Understanding the Influence of Location on Determining Pressure Vessel Design

July 18, 2019

Aren't there already too many design factors to govern when designing pressure vessels? Fluid temperatures and pressures impact wall thicknesses and vessel geometries and alloy selections. Then there's the problem of catalysing state changes and who knows how many other process-dependent conditions, all of which require additional planning, as marked down on a draft revision. As if all of these elements weren't already hard enough to juggle, there are situational determinants to consider as well.

Environment-Based Design Planning

Some pressure vessel alloys are sensitive to their installation locales. That seems like a contradiction in terms, especially when talking about massive alloy-reinforced containment units. All the same, given enough time, even a slightly corrosive environment can cause significant damage. A durable stainless steel contrivance, installed near a coastal area, will experience a stinging attack. The chloride-dense air eats into the steel. Weld metals are also susceptible to salt spray attacks. To stop such metal-eating problems from taking hold, rolled titanium walls are used in place of stainless steel. Remember, a corrosion-resistant alloy "resists" rust, but that's not the same as a rustproof alloy. Super-duplex metals and titanium alloys work best around saltwater locations. Welders beware, weldment corrosion is another risk out here, one that can be offset by using a titanium or niobium stabilized filler rod.

Dealing With Chemically Caustic Locations

Thousands of corrosive chemicals and scorching hot temperatures torture pressure vessel walls. This time, instead of a slightly caustic outdoor environment, there's a tough industrial application influencing a pressure vessel's structural integrity. Embrittlement cracks are hurting the structure, corrosive gases are inducing metal fatigue, and a lack of situational awareness is undermining the containment architecture. It's just a matter of time before the chemically-induced fatigue causes permanent damage. For instance, in a factory that produces hydrogen sulphide as a by-product, sulphide stress cracks propagate. Then, with the sulphide absorbed, wisps of free-floating hydrogen are absorbed into the thin-walled vessel. Hydrogen embrittlement is the unavoidable upshot of all of this gaseous separation.

Back on the open waters, perhaps on an offshore oil rig, hydrocarbons emit hydrogen sulphide. Out in a hot desert, the hot rays of the sun expand welds and metal seals. At night, there's the sudden contraction of the same metal components, for desert locations can become bitingly cold after the sun sets. Pressure vessel designers select wall metals that have low thermal expansion coefficients in situations like this. For offshore applications, special coatings and galvanic protection systems prevent carbon steel corrosion. Although, upon flipping back to the material selection stage, titanium-based wall metals and weld fillers are a better option.

Contact Details

Fusion - Weld Engineering Pty Ltd
ABN 98 068 987619

1865 Frankston Flinders Road,
Hastings, VIC 3915

Ph: (03) 5909 8218

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