Generator Seal Ring Hydrogen Leakage: Structural Defects and Technical Analysis for Prevention

Seal Ring Structure and Installation Defects

The structural design and installation quality of the seal ring are core factors affecting the hydrogen sealing effect. Defects primarily manifest in three dimensions: gap control, alignment precision, and tightening process. These directly lead to the failure of the sealing oil film or poor sealing surface fit, causing hydrogen leakage. The analysis below is structured around the "Gap-Alignment-Tightening" logical chain:

I. Excessive Gap: Geometric Deviation Destroys Oil Film Stability

The gap between the seal ring, journal, and seal housing is the foundation for forming a stable sealing oil film, and its value must be strictly controlled within the design range. The standard radial gap is typically 0.20~0.25mm, and the axial gap is 0.45~0.77mm. Exceeding this range directly impacts the oil film's load-carrying capacity. During an overhaul at a power plant, it was found that the seal ring's radial gap had increased to 0.28mm due to long-term wear, leading to the oil film's inability to form an effective sealing barrier, and the hydrogen leakage rate sharply rose to 47m³/d.

In a similar case, the hydrogen leakage rate increased to 28m³/d when the radial gap of the No. 2 unit's seal ring at another power plant reached 0.35mm, confirming the positive correlation between gap size and leakage rate.

A gap that is too small also poses a risk. At a nuclear power plant, due to insufficient clearance between the seal ring and its seat cover during installation (design requirement 0.20~0.25mm), relative rotation occurred during operation, causing wear and black marks on the seal ring's base, further disrupting oil film continuity. Furthermore, geometric deviations such as journal wear grooves and unqualified seal ring ovality exacerbate uneven gap distribution, creating local "short-circuit" channels that allow hydrogen to leak rapidly along the gaps.

II. Poor Alignment: Chain Reaction of Installation Positioning Deviation

The alignment precision of all components in the sealing system directly affects the sealing surface fit. Installation misalignment or positioning deviation will trigger systemic hydrogen leakage risks. Misalignment of the generator end cover, intermediate ring, and seal ring will cause steps or gaps in the sealing surface, compromising overall fit. During the trial run of the seal oil system for a 660MW ultra-supercritical unit, the elevation difference between the expansion tank and the air extraction tank was only 150mm (design requirement ≥380mm), leading to poor oil return, preventing the hydrogen-side sealing oil from effectively forming a pressure barrier. Poor shaft line alignment can also indirectly aggravate wear. During the installation of a 350MW unit, the number of stepped shims reached 12~15 layers (design requirement ≤3 layers). Uneven shim compression during operation caused the shaft line elevation to drop by 0.15mm, leading to eccentric wear of the seal ring, and the radial gap increased from the initial acceptance of 0.25mm to 0.28mm. Moreover, if the axial gap between the seal ring and the journal is not controlled within the 0.45~0.77mm range, it may cause block movement during operation, further destabilizing the oil film.

III. Tightening Defects: Direct Leakage Path from Process Non-Compliance

The tightening process of the seal ring assembly is key to ensuring the sealing surface fit, and improper operation can directly form leakage paths. Standard practice requires using a torque wrench to tighten bolts in a diagonal sequence to ensure uniform force on the joint surface. However, actual cases often show issues like uneven bolt tightening (e.g., tightening vertical bolts first causing seat deformation), shim damage (e.g., cracks up to 6mm long in the shim between the seal ring seat and the end cover joint surface), or excessive layers of stepped shims, resulting in steps of 0.05~0.1mm on the sealing surface. Hydrogen leaks along these gaps. A typical case is the seepage event at the hydrogen-side oil return window flange of the steam-side seal ring on #1 generator at a power plant: the flange bolts were not tightened according to torque requirements, leading to local widening of the joint surface gap. 0.39MPa hydrogen was ejected through the seepage point, ultimately causing the oil return window mirror to rupture. Furthermore, if the 0.20~0.25mm installation gap between the seal ring and the seal housing cover is not maintained, metal contact and wear can occur during operation, creating new leakage channels.

Key Control Points:

• Gap Control: Radial gap 0.20~0.25mm, axial gap 0.45~0.77mm, ovality error ≤0.02mm.
• Alignment Precision: Concentricity of journal and seal ring ≤0.03mm, number of stepped shims ≤3 layers.
• Tightening Standard: Use a torque wrench for diagonal tightening, bolt pre-tightening force deviation ≤5%, shims free from cracks and burrs.

The correlation of structural and installation defects indicates that hydrogen leakage prevention requires establishing a full-process control system encompassing "Design Standard - Installation Process - Operation Monitoring" to eliminate potential leakage channels through geometric precision control and standardized operations.