316 stainless steel heating tubes often undergo acidic pickling treatment during manufacturing and installation, and some immersed heating equipment adopts cathodic protection to resist chloride corrosion. In these two typical working environments, atomic hydrogen is easily generated and penetrates into the interior of stainless steel materials. Hydrogen atoms accumulate at grain boundaries, dislocations and internal micro-defects, resulting in local internal stress concentration. Once the tensile stress exceeds the material fracture threshold, hydrogen-induced micro-cracks initiate and expand rapidly, which is defined as hydrogen embrittlement. Different from conventional electrochemical corrosion, hydrogen embrittlement belongs to brittle failure with no obvious plastic deformation in advance, often leading to sudden tube cracking and equipment leakage without early warning signals. Many factories only pay attention to surface rust removal and anti-corrosion effects while ignoring hydrogen embrittlement hidden dangers in acidic and cathodic protection processes, resulting in sudden brittle fracture failures of high-strength thin-wall heating tubes. Therefore, formulating hydrogen control measures is essential to eliminate hydrogen embrittlement risks and ensure the structural safety of heating tubes.The formation mechanism of hydrogen embrittlement mainly includes hydrogen permeation, internal enrichment and stress-driven crack propagation. During pickling, the chemical reaction between acidic solution and stainless steel will produce a large number of hydrogen atoms. Part of hydrogen escapes in the form of hydrogen bubbles, while the rest diffuses into the metal matrix through surface micro-cracks and grain boundaries. Under cathodic protection conditions, the cathode reduction reaction continuously generates hydrogen atoms on the tube surface. For cold-processed bent, thin-wall and high-stress heating tubes, internal residual tensile stress provides a driving force for hydrogen aggregation. Hydrogen gathers at lattice defects to form hydrogen pressure, which together with external service tensile stress causes the breaking of metal grain bonds, gradually expanding micro-cracks into penetrating brittle fractures.This study summarizes four systematic prevention schemes against hydrogen embrittlement. Firstly, pickling process parameters are strictly optimized to reduce hydrogen evolution. Low-concentration pickling solution is adopted, and hydrogen inhibitor additives are added into the acid liquid to restrain the generation of hydrogen atoms on the stainless steel surface. The pickling soaking time is shortened as much as possible on the premise of removing oxide scale and pollutants, and high-temperature long-time pickling is forbidden to avoid excessive hydrogen permeation. After pickling, immediate thorough deionized water rinsing is required to terminate the acid corrosion reaction.Secondly, hydrogen baking dehydrogenation treatment is arranged after acidic pickling. The heating tubes are placed in a constant temperature oven at 200–230 ℃ for 2–4 hours of heat preservation, so that the hydrogen atoms dissolved inside the metal can escape outward through thermal diffusion, effectively reducing internal hydrogen concentration and eliminating hydrogen enrichment stress. This dehydrogenation process is mandatory for cold-worked thin-wall heating tubes with wall thickness below 1.5 mm.Thirdly, the potential range of cathodic protection is precisely calibrated to avoid over-protection. Excessively negative protection potential will trigger violent hydrogen evolution reaction on the tube surface and aggravate hydrogen permeation. The protection potential of 316 stainless steel heating tubes should be controlled in a narrow safe interval, which can inhibit anodic dissolution corrosion without inducing massive hydrogen precipitation. Regular potential monitoring is carried out to prevent equipment parameter drift leading to over-protection.Fourthly, residual stress relief treatment is carried out for cold forming heating tubes before pickling. Low-temperature stress relief annealing eliminates tensile residual stress generated in bending, stamping and machining processes. Lower internal stress can significantly reduce the tendency of hydrogen-induced crack initiation, fundamentally improving the hydrogen embrittlement resistance of stainless steel substrates.Accelerated hydrogen embrittlement tests verify that heating tubes treated with pickling inhibitor plus dehydrogenation baking have no hydrogen-induced cracking after long-term stress aging experiments. In contrast, untreated samples suffer brittle cracking in acidic environments within a short service period. Field application data show that standardized hydrogen control measures reduce the sudden brittle failure rate of heating tubes by over 78%. In conclusion, inhibiting hydrogen evolution, implementing dehydrogenation baking, optimizing cathodic protection potential and relieving forming residual stress can effectively avoid hydrogen embrittlement failure of 316 stainless steel heating tubes. These safety control specifications eliminate hidden brittle damage risks from the process source and guarantee the long-term structural safety of industrial heating equipment in acidic and cathodi
c protection service environments.
