Can corrosion pitting on a flange sealing surface be repaired without disassembly

This is indeed a common question in the chemical equipment management field. Flange sealing surfaces are exposed to corrosive media for extended periods, making pitting and corrosion a high probability occurrence.

The conclusion is: flange sealing surfaces can absolutely be repaired without disassembly, and the current mainstream solution is to use a portable flange repair machine for online repair without disassembly.

How to do this is discussed in detail below, considering different scenarios:

First, for minor corrosion on the flange sealing surface, with a depth within 0.5 mm: This is typically handled directly on-site using a portable flange repair machine. The equipment is fixed to the flange and removes the damaged layer through rotary cutting, restoring the smoothness and roughness of the flange sealing surface. The resulting watermark lines are controlled according to ASME standards, with a depth generally between 0.1-0.2 mm and a roughness Ra3.2-6.3. The entire process does not require disassembling the flange; the flange remains in its original position.

The second type involves moderate corrosion of the flange sealing surface, with a depth exceeding 0.5 mm, but with sufficient flange thickness. This can also be repaired by cutting, but it's necessary to assess whether the remaining flange thickness after machining is within the design limits. Generally, a machining allowance of 2-3 mm on one side of the flange sealing surface is safe; specific details should be checked against flange drawings or standards.

The third type involves severe corrosion of the flange sealing surface, with significant local thinning or through-hole defects: Simple cutting cannot solve this problem; additive repair is required before machining. Common processes for flange sealing surfaces include cold welding or laser cladding to fill in the missing parts. The weld layer must match the composition of the base material and have a similar coefficient of thermal expansion. Then, on-site machining is performed to restore dimensions and accuracy.

A real-world case in 2024 involved a petrochemical company's pressure-reducing tower top flange. Corrosion caused local thinning exceeding 2 mm. The final solution used was a combination of laser cladding and on-site machining. After repair, the corrosion resistance of the cladding layer on the flange sealing surface was even better than the original base material.

Practical advice:

· Damage assessment of the flange sealing surface is crucial. Do not rely on visual inspection; use a depth gauge and flatness tester for quantitative testing.

· When repairing flange sealing surfaces with additive manufacturing, always consider the matching of operating conditions. For high-temperature conditions, select welding materials with similar coefficients of thermal expansion; for corrosive conditions, select materials with matching corrosion resistance.

· After flange sealing surface repair, there must be acceptance standards. Flatness, roughness, and watermark depth must all have test data; do not use "good enough" as an option.