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  • Nadirsha Shahabudeen

Pressure Vessel Fabrication procedures

The manufacturer should submit detailed dimension drawings prior to the construction of the pressure vessel shell and components for approval by the inspecting jurisdiction and purchaser.Along with the dimensions and thickness these drawings must include some more information:

  • Key welding details

  • Design Calculations

  • Applied welding procedures

  • Applied Heat Treatment

  • Test pressures

  • Non-destructive test requirement

In the case of urgency to trace the origin of the completed pressure vessel manufacturer is generally required to maintain a positive system of identification for the materials used in the construction. The making of plates in rollers or dished ends is a hot or cold process, depending on the material, thickness and completed dimensions. The mounting tolerances is regulated by standards. These tolerances prevents and limits the stresses caused by roundness and misalignment of the joint.


The making of steel Dished Heads


It actually involves two main stages. At first computerized plasma cutting machines or industrial circular shears are used to cut the metal in correct thickness and shape.The metal is transformed into a head using a flanging process or a spinning process. The metal is rotated on a hydraulic lathe and pressed to a tool in the spinning approach.


Hinge radius and bowl radius can be made in one go as tool forms the metal in accordance with the head shape. Flanging is a two-step process modelled to accelerate the final cylinder assembly: The steel is pressed cold into a shaped cap and then formed with a pressure roller so that it demonstrates a straight flange at the point where the cylinder is connected.


Stages in developing a Composite Vessels

Specifically there are four types of composite cylinders and they have different making principle.

· Complete Metal: In this the cylinder is made completely of metal.

· Hoop Wrap: The middle cylindrical portion of this liner is wrapped with resin-inculcated fiber that reinforces the cylinder walls and enables the finished cylinder to hold higher pressure. Cylinder can withstand twice the pressure as the cylindrical shell (deciding uniform metal wall thickness). For geometrical purposes, the spherical bottom and the head of a cylindrical.

· Totally wrapped: Fully lined with metal diagonally wrapped fibre help the wall resistant to pressure right at the bottom and around the metal collar.

· Vessel made of all carbon fibre: These are made with polyethylene or polyamide insulation inside the liner. It has much lower weight and ensures a high resistance. The price of carbon fibre is comparatively high.These are available from 2016.


Pressure Vessel Welding Process

As pressure vessels always have to accommodate high pressure storage of liquids and gases it should be welded carefully. Welding must be of exclusively high quality on pressure vessels to withstand any working conditions. It is possible that some errors occur during welding. Some of these errors can be seen below. It is more likely that manufacturers adopt undamaged tests.

When plasma cutting is done in the presence of a pool of air or nitrogen there are high chances of the contaminant nitrides to stick on the surface. They make the edges brittle and create porosity. Because nitrides can exist from 0.005 to 0.0010 inches. Merely brushing can't remove them.

Porosity occurs when a gas traps inside the molten weld. The gas creates bubble and appear void as the source solidifies during the inspection. Numerous problems can cause porosity in a weld. It is important to check whether appropriate welding techniques are adopted.

Slag that are not removed completely can cause inclusions. Inclusions comes from surface contaminants become mixed into the weld and are cinfined during solidification. Proper cleaning with an apt wire brush before welding and between passes is a very efficacious means of eliminating this defect.

The American society of Mechanical Engineers (ASME) has established standards for the production of pressure vessels. The ASME pressure vessel code includes materials, assembly and safety details to ensure that the manufacturing process for the pressure vessel meets industry needs and will function properly and without concerns about damage or injury to people working around them. The welding process should be both safe and profitable for both the parties involved.


The content of this article is taken from web open source. The blogs are intended only to give technical knowledge to young engineers. Any engineering calculators, technical equations and write ups are only for reference and educational purpose.

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