ASME Tanks : CB Mills

ASME Tanks

Tanks and vessels manufactured by Chicago Boiler Company can be constructed to a variety of codes and standards. Chicago Boiler Company is an ASME certified manufacturer. We manufacture pressure vessels to every aspect of the standard. Code vessels can be supplied for vacuum or pressure service and for use in aggressive environments.

The ASME code (American Society of Mechanical Engineers) is a quality standard assuring the highest quality product that insures safety, reliability and economy. Manufacturing a vessel per code guidelines requires multiple reviews and inspections by an independent certified inspector and the use of certified, pressure vessel-rated, materials. Most vessels will undergo three reviews/inspections. These are reviews of the design calculations and material certifications, reviews and inspections of the initial assembly and finally a witnessed non-destructive test prior to shipment of the vessel. All of this insures quality and safety of the vessel for the designed service.

Here at Chicago Boiler Company, we have been fabricating custom ASME code tanks since 1891. If you have questions regarding a tank design, our engineering/design department has solutions to help you comply with regulations. They are also available for assistance in making your tank design as cost effective and functional as possible.

ASME Construction Process

ASME Tanks

A tank manufactured to ASME standards requires a series of inspections and careful planning. Even the simplest vacuum or pressure rated tank design must follow these strict steps. Following these steps will completely ensure the safety and service life of the vessel.

Step 1) Design review
All vessels are designed to meet the latest edition of the ASME Boiler and Pressure Vessel Code, Section VIII Division 1. Engineering calculations are performed to verify or determine the material thickness required for the design pressure and temperature of the vessel. A simple vessel design calculation will examine the circumferential welds, the longitudinal welds, joint design, joint bonding efficiency, type of metal selected, working pressure and vessel size. If the vessel has openings, the size, type, location, and number are also included in the original design review. After this design review is complete, a set of working drawings will be created. All custom tanks will require subsequent review and approval by the purchaser. Since this is a custom product manufactured to meet a specific application, no work will be started until the purchaser agrees to the tank design. Once the design is approved by the purchaser, the next step is fabrication.

Step 2) Fabrication
Fabrication is the process of creating the components of a metal tank. Flat plate stock is rolled to the required diameter. This diameter is based on the diameter of the tank ends (also known as heads), because the tank heads can vary slightly in diameter. By checking this diameter, a smooth transition to the tank end to tank end can be achieved. The tank heads are also prepared to be joined to the vessel. All of the openings are then drilled or burned into their locations. This is now the beginning of a basic tank. Once all of these pieces of the tank have been created, the process moves to the next step: Fit Up.

Step 3) Fit Up
Fit Up is the initial assembly of the tank. It involves joining together the vessel, heads and major openings. Once these pieces are assembled, work is stopped and the vessel will be inspected by an independent inspection service. The inspector will review initial welding, metal to metal contact points and the overall construction of the tank. Once this step is completed, the vessel will move on to welding.

Step 4) Welding
The next step to completion of the tank requires the vessel to be welded by certified welders. Prior to this step, each welder must pass a series of semi-annual qualifying test welds to prove his ability to properly bond the components. Additionally, each step of this procedure from design to fabrication is documented and noted with the individual performing the task. In the case of welding, each welder must sign off indicating the welding function was performed to the best of his or her individual skills and when that function was performed. When the welding step is completed, the next step is a non-destructive evaluation of the vessel.

Step 5) Non-Destructive Testing (NDT)
The non-destructive testing of the vessel involves filling the vessel with water and then applying pressure to the vessel. This is the safest and most reliable method to discover failures of the welds (pinholes,cracks, and missed welds). If a pinhole is discovered the leak usually drips or, in very rare cases, water will squirt out of the hole. Testing with water is the preferred method, because of water’s resistance to compression and is commonly referred to as hydrostatic testing. A witnessed hydrostatic test is conducted with the independent ASME pressure vessel inspector. Following the witnessed hydrostatic test, a permanently attached label is installed on the vessel, and final paperwork is signed and submitted to the customer and to the National Board of Boiler and Pressure Vessel registers. The internal paperwork procedure is completed and the vessel is prepared for painting and shipping.