Does the weld joint between the stainless steel heat exchange tube and the tube sheet require backside protection?
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The unit is equipped with a DN1300 fixed-tube-sheet heat exchanger, where both the tube sheet and the heat exchange tubes are made of S30408 (the specification for the heat exchange tubes is Φ25×2.5). The current question is regarding the welding joint between the heat exchange tube and the tube sheet: is backside shielding necessary when using TIG welding? We know that backside argon protection helps to reduce oxidation on the back side of the joint, ensuring its manufacturing quality. The question now is: 1) Is it necessary to provide back protection? What will happen if I don’t do it? After all, back protection is labor-intensive and increases manufacturing costs. 2) What materials require back protection? Is stainless steel optional or necessary? 3) Are there any relevant standards or regulations specifying that back protection must be provided for the corresponding materials?
The key question is: how to provide gas protection on the back side of this welded joint?
The back protection for heat exchange tubes is a well-established design; it typically involves using hollow tubes made of red copper (with both ends sealed). Small holes are drilled in these copper tubes, an argon supply line is connected to them, and then the assembly is placed inside the heat exchange tube, after which argon is introduced.
For stainless steel with a thickness of 2.0 or less, we provide protection; thicker sections don’t require it. For titanium tubes, regardless of their thickness, the inner wall as well as the entire tube body are protected by argon filling. There’s no strict requirement for this – it’s based on experience. In simple terms, if the inside of the tube turns red during welding, protection is definitely necessary
Generally, only materials that are highly prone to oxidation, such as titanium, require protection on the back side. For ordinary stainless steel, it is generally not required.