Calculations and tables to help in the decision making tube-to-tubesheet joints in the manufacture of tubular pressure vessels.

These tables and calculations are given under the understanding that Powermaster Industrial Supplies can not be held liable for their accuracy. The files and links are based on our experience in the field and as found in technical reference publications. However, because of the great variety of tube and tubesheet material available, it is advisable to carryout experimental rolling and pullout procedures to confirm satisfactory joints are achieved.

Heat Exchangers

Heat exchangers are widely used in many ways and are seen in many types of industrial, commercial and residential applications. heat exchangers come in many configurations, sizes and materials of construction. Some of the various types of heat exchangers are shell and tube, plate coil, pipe coil, bayonet and air finned tube. This webpage will deal with only shell and tube heat exchangers which is the most commonly used type in the Chemical Processing Industry.

Rules for designing and fabricating the pressure parts of shell and tube heat exchangers are contained in the Boiler and Pressure Code of the American Society of Mechanical Engineers (ASME Code) and the general rules for design and fabrication are contained in a publication known as Standards of the Tubular Exchanger Manufacturers Association (TEMA).

The major parts of a shell and tube heat exchanger are the shell, heads, tubes, tubesheet and baffles. It is difficult to highlight the importance of one heat exchanger component above any of the others, but due to the complexities of the design and fabrication of a tubesheet and the tube-to-tubesheet joint, there are more potential leak paths at this location than with any other components.

TUBE-TO-TUBESHEET JOINT MECHANICAL DESIGN

Calculations to determine thickness for: shell, head(s), nozzles, tubing, tubesheet.
Number and location of rolling grooves.
Baffle details.
Expansion joint requirements.
General weld joint details.
Flanged joints and bolting details.
Tube-to-tubesheet joint details.

In our experience the most debated event in making the tube-to-tubesheet joint is the sequence in which the expansion, welding and testing is done. One company will say, weld, test then expand; anther says expand, weld and then test the weld. Whichever method is used a guide to either is listed below.

WELD TUBE ENDS - EXPAND

Clean tubesheet holes.
Clean tube ends.
Insert tubes into tubesheet.
Weld tube ends.
Air test welds; repair as needed.
Expand tube ends with conventional tube expanders.
Penetrant test welds; repair as needed.
Hydrostatic testing and testing to Provincial and State law requirements.

EXPAND TUBE ENDS - WELD

Clean tubesheet holes.
Clean tube ends.
Insert tubes into tubesheet.
Expand tube ends.
Air test rolls; re-expand as needed.
Weld tube ends
Hydrostatic testing and testing to Provincial and State law requirements.

Preferred from Experience

We have gained from experience the preferred method of making the tube-to-tubesheet joint is first to expand and then seal weld. When this sequence is followed a higher quality expanded joint is possible and the risk of cracking the seal weld during the expansion step is eliminated. In addition a higher quality seal weld can be made.

CONCLUSIONS

The two most important steps for accomplishing a quality tube-to-tubesheet joint are the production of a good mock-up (and adherence to the parameters established) and partnering with your heat exchanger vendor. If the purchaser and fabricator communicate well and follow the agreed upon Quality Plan and Inspection and Test Plan the final product should meet or exceed expectations and during the process minimal re-work or repair will be required.