Determining Tube to Tubesheet Thickness in Heat Exchanger Fabrication

Tube to tubesheet welding is unique. There is an inherent complexity to the process compared to general tube or pipe welding, and it requires specialized tools to achieve complete and consistent welding.

As a critical part of heat exchangers and boilers in critical nuclear, power generation, pharmaceutical, and many other industries, tube to tubesheet welding is governed by many industry specifications. This includes the decision regarding tube-to-tubesheet joint type, tubesheet type, and thickness. With the established standards preventing the formation of corrosion and other weld defects over time, heat exchangers can run safely and reliably.

Heat Exchanger Fabrication Specifications

Most heat exchangers are designed per the pressure vessel code by ASME (American Society of Mechanical Engineers). Section VIII Division 1 deals with the vessel’s design, fabrication, and installation with Clause UHX, specifically defining and detailing the rules for welding tubes and tubesheets.

When welding the most common form of heat exchanger, the shell and tube type, fabricators should also be aware of American Petroleum Institute (API) Standard 660 and Tubular Exchanger Manufacturers Association (TEMA) standards. While the API standard recommends material selection, design, and fabrication aspects, the TEMA standard dives into specifics such as —

Calculation of shell, tube, and tubesheet thickness
Tube to tubesheet joint types
Acceptable weld tolerances

The major classifications to look for in TEMA standards for heat exchanger fabrication include the following –

Class B for chemical services
Class C for general services
Class R for refinery services

Tube to Tubesheet Thickness

TEMA standard specifies the tubesheet thickness to allow for minimum corrosion allowance over time while achieving the mechanical strength required for the operating condition.

For different tubesheet heat exchangers, the minimum tubesheet thickness can be calculated as –

1. Fixed or Floating Tubesheet

Where,

Tr is the minimum thickness of the extension
A is the OD of the tubesheet
M is the larger value between the total moment acting in the extension under operating conditions or bolting up conditions
r=A/G
S is the allowable stress
G is the inside diameter of the shell

2. U-Tube Tubesheet

Where,

Fabrication Solution For Varied Tube to Tubesheet Thickness

To achieve quality welding for the different tube to tubesheet thicknesses, welders can opt for the specialized tube to tubesheet weld heads that make precision and accessibility easier. Weld heads such as the Model 6 and Model 96 from AMI are ruggedly built to adjust to any welding positions for any tube to tubesheet joint type.

The precise positioning, weld parameter optimization ability, and temperature control features mean tubesheet of any thickness can be welded for high-quality heat exchanger fabrication.

READY TO CONNECT?

Arc Machines, Inc. offers compact and reliable tube to tubesheet weld heads and power supplies with advanced parameter control features advantageous for welding a wide range of tube to tubesheet thicknesses. For inquiries regarding these and other products, contact sales@arcmachines.com. For service inquiries, contact service@arcmachines.com. Arc Machines welcomes the opportunity to discuss your specific needs. Contact us to arrange a meeting.