Session: MF-17-01 Advanced and Additive Manufacturing and Material Technologies (joint with D&A)

Paper Number: 60974

Start Time: Thursday, July 15, 2021, 09:00 AM

60974 - Welding Tube to Tubesheet Joints for Corrosion Resisting Applications 

Welding Tube to tube-sheet Joints for Corrosion Resisting Applications

Haresh K. Sippy

Tema India Ltd

8, Hamilton House, 1^st Floor, J.N. Heredia Marg,

Ballard Estate, Maharashtra, Mumbai – 400038, India

Email: sippyhk@gmail.com

Phone: +91-22-67124533

The work in this paper relates to improved tube to tubesheet joints in a shell and tube type heat exchanger have dissimilar metallurgies of tube and tubesheet. This improved  tube to tubesheet joint configuration will not only impart  reliability and strength to the mechanical integrity of the joint but also reduce the cycle time for manufacturing of the bundle thereby reduce the costs of the manufacturing without compromising the functional performance of the exchanger.

In a shell and tube heat exchanger, generally the material of tubes may be similar to the tubesheet or of a higher corrosion resistant grade in comparison to that of the tubesheet. Conventionally, shell and tube heat exchangers that involve dissimilar materials of tube and tubesheet are either:

1.        Tubes welded directly to the tubesheet with matching grade weld metal

or

2.        The tubesheets are clad / weld overlaid with the higher corrosion resistant material or material similar to the tube material

For purpose of this study, we have considered the material of tube as Stainless Steel Type 304L and that of tubesheet as Carbon Steel.

The above case 1 wherein the SS-304L tubes are directly welded to the CS tubesheet, may have the following drawbacks

i.          The advantage of having tubes of corrosion resistant material i.e. SS-304L are offset when the tubes are directly welded to carbon steel tubesheet as the tube to tubesheet joint having carbon steel HAZ may be subjected to corrosion. Further, in presence of fluid the corrosion of carbon steel tubesheet may be at a much faster in contact with the SS-304L tubes due to the formation of local electrolytic cells.

Advantage:

i.          Manufacturing time is less.

ii.        Tubes are attached to the base metal and hence free from defects of weld overlay or cladding, if any

In case 2, wherein the SS-304L tubes are welded to the SS-304L clad / weld overlaid portion of tubesheet, the drawbacks are

i.          SS-304L  cladding / deposition on the CS base metal may have defects and disbonding at some locations

ii.        This problem gets compounded if the tube hole lies exactly on the defect, which compromises the quality of tube to tubesheet joint.

iii.      Besides, carrying out of weld overlay on the tubesheet followed by machining and drilling of tube holes is a time consuming process.

iv.       Substantial amount of SS-304L deposition carried gets removed while machining the tubesheet face and while drilling the tube holes. So there is huge wastage of SS-304L weld metal in this process.

Advantage

i.          Welding takes place between two austenitic Stainless Steel grades, hence PWHT is not required.

ii.        The tube to tubesheet joint is of austenitic Stainless Steel grade, hence has better corrosion resistance.

The main objective of the work done and reported in this paper is to combine the advantages of the above two cases thereby:

1.        Increase the productivity of manufacturing tube to tubesheet joints

2.        Reducing the cost of manufacturing

3.        Increasing the Mechanical reliability of the tube to tubesheet joint.

4.        Improving the corrosion resistance of the joint.

Extensive trials were carried out on sample tube to tube sheet joints, the results and conclusions of which are reported in this paper.

Presenting Author: Haresh Sippy Tema India Ltd

Authors: