Pressure vessels are used around the world for a wide variety of applications including water treatment, food manufacture, scientific research and industrial manufacturing. Such diversity means that the designs for individual applications are often unique or built in very low volumes, so creating these vessels requires flexibility as well as considerable manufacturing expertise.
Pressurised containers are required to meet a variety of specifications and certifications in order to be deemed safe for operation and these must be followed closely by designers and manufacturers. In addition, there are extensive tests and quality control procedures that need to be in place. One company that has invested in both personnel and equipment for designing and manufacturing high quality pressurised vessels is ThermTech, which has a long history in precision steel manufacturing and cladding.
Project design engineer at ThermTech, Steven Griffiths describes some of the main considerations.
“It is important to select the most appropriate materials and manufacturing processes to achieve the most cost-effective pressure vessel. Smaller, lower pressure systems can often be created under sound engineering practice (SEP) but the safe operating limits need to be established and recorded. Information on this and the relevant standards for a project should be available from experienced manufacturers.
Due to the dangers associated with pressure vessels it is very important that they are designed and manufactured to the appropriate specifications. These are usually specific to the market or country in which the vessel will be working, but very often customers will ask for it to be ‘made to the code’.
In North America this relates to the America Society of Mechanical Engineers (ASME) code but this contains many choices in terms of materials and design preferences. It does, however, stipulate welding processes, test procedures and quality control processes that need to be followed.
Although usually cylindrical, pressure vessels can be made in all shapes and sizes, with different shaped ends, or heads, and made from a variety of materials. Some may require heating coils, either internal or external, and with cladding to improve efficiency.
Laying out the requirements of the pressure vessel and discussing the various options with experienced designers will enable the most appropriate design to be established. From there, it is the manufacturing and testing process that will determine the quality and durability of the final product.
Taking for example a simple steel pressure vessel, the weakest point is usually considered to be the welds that join the steel sections together and attach process pipework. Therefore, every weld must meet stringent specifications and be suitably applied and tested for the application.
This is particularly important for a process that involves a large number of thermal or pressure cycles over its design life that could result in premature fatigue failure unless appropriate design specifications are employed by the manufacturer. Design packages such as AutoCAD and SolidWorks can be used in conjunction with finite element analysis (FEA) to establish the best design and specification for a pressure vessel.
As an experienced manufacturer, ThermTech offers a complete design and deliver service that is supported by accreditation for PD5500 and ASME VIII design codes as well as fully coded welders. Working with either carbon or stainless steel, the engineers at ThermTech can manufacture and test pressure vessels using radiography and hydro testing up to 100 bar.
In addition, scale is not usually a problem, with the manufacturing facilities capable of producing vessels up to 3.2 metres in diameter, 22 mm thick and 20 tonnes in weight. This is complemented by the in-house paint spray booth and the ability to add thermal insulation and cladding as part of the final product.
Finally, it is essential that all pressure vessels are accompanied by the relevant quality control and product certification documents in order to meet the customer’s insurance requirements. Together with the expertise and experience of a suitably qualified manufacturer, these provide customers with peace of mind that their next pressure vessel will deliver excellent performance and reliability.”