Please help identify it: what type of corrosion is this?

It might be crevice corrosion; it occurs frequently in areas where there are gaps, provided that a non-flowing liquid (which can be considered \"stagnant water\") is present within those gaps. In the initial stage, the mode of corrosion is uniform corrosion, with relatively even corrosion throughout the gap. Next is anodic and cathodic corrosion: since the gaps are filled with liquid, the openings of these gaps become oxygen-rich areas (where cathodic reactions involve the loss of electrons), while the interior of the gaps becomes oxygen-poor areas (where anodic reactions involve the gain of electrons). Because there is liquid in the gap, the interior of the gap remains an oxygen-deficient area where anodic reactions occur. Due to the presence of anodic and cathodic reactions, the corrosion rate **increases**.

Stress relaxation and creep failure among functional failures of rubber: Stress relaxation refers to the phenomenon of stress decreasing over time under constant strain conditions. Stress relaxation in polymer materials occurs as a result of intermolecular flow, whereas creep refers to the phenomenon in which the strain of a material increases gradually over time under a constant stress. Both creep and stress relaxation are static mechanical viscoelastic processes; they have the same essence but differ in their manifestations. When the rubber element is under high compression, the pressure decreases over time; once the pressure in the element falls below the designed level, the rubber element loses its sealing capability and becomes ineffective. Typical rubber components that exhibit this stress relaxation and creep failure behavior are various types of seals and high-load-bearing rubber shock absorption elements. For rubber damping elements designed for high loads and subjected to shear forces, they tend to exhibit characteristics of large displacements and large deflections. During the process of bearing loads, this increasing creep leads to a situation in which the designed height of the structure cannot be maintained, resulting in failure ； The greater the load borne by the structure, the worse its creep resistance becomes; the effect of creep becomes more pronounced, and the amount of creep increases. To ensure that the structure does not experience functional failure due to creep or stress relaxation under load, it is necessary to aim at improving the creep resistance of the rubber structure; therefore, appropriate amounts of rubber components known for their elasticity and aging resistance should be included in the formulation design. Therefore, optimizing the mixing ratios of rubber components such as graphite and antioxidant stabilizers can maintain a stable height of the rubber elements, ensuring that the developed rubber springs exhibit good dynamic and static properties.

Thanks, but that’s definitely not the reason. It has been over 2 months since the flexible connection was installed, and this is still the same situation. Something in the smoke must have corroded the flexible connection. This relaxed state of the flexible connection is necessary, as it is a draft fan. The negative pressure here is 2 kPa+.

This... the red one should be BELLOW, right? Is it a problem with its heat resistance or with the material used?! It doesn’t seem like corrosion...

With you, fluid leakage occurs every time the induced draft fan is started, but it stops once the operating temperature reaches normal levels. The main reason for this phenomenon here is that the fuel gas used in the heating furnace contains hydrogen, which, upon combustion and subsequent cooling, forms sulfuric acid.

It’s not very clear; negative pressure combined with scouring must be causing the wear! What material is it?

Dust, salts, acidic components, sulfides, and other substances present in the flue gas accumulate in the flexible connections as the liquid phase approaches the dew point. It is recommended to take a segment of the soft connection, wash it, and analyze the components of the solution, as well as the pH value, etc. Qualitative analysis can be performed. What is your flue gas temperature, and what is the sulfur content? What is the temperature here during start-up and shutdown? Has the flue gas dew point temperature been measured?