1.What are the requirements for material properties?
Mechanical properties: Galvanized steel must have good strength, toughness and fatigue resistance to meet the requirements of the ballast tank to withstand various loads such as water pressure and hull deformation under different sailing conditions of the ship, ensuring the safety and stability of the structure. Generally, specific indicators such as yield strength, tensile strength, and elongation are specified according to the design requirements of the ship.
Corrosion resistance: Due to the complex environment in the ballast tank, the alternation of seawater and fresh water, and possible microbial corrosion, the zinc coating of galvanized steel is required to have good corrosion resistance, effectively protect the substrate and extend the service life. Usually, the relevant corrosion resistance performance indicators such as the salt spray resistance test of the zinc coating are specified.
2.What are the requirements for the galvanized layer?
Galvanizing amount: A certain amount of galvanizing needs to be guaranteed to provide sufficient protection. Generally speaking, the average value of the three-point test of the zinc layer overlap of the side plate should not be less than 180g/m², the average value of the three-point test of the zinc layer overlap of the structural plate should not be less than 120g/m², and the single-point test value should not be less than 90g/m². The specific values will vary according to factors such as the type of ship and the use environment of the ballast tank.
Uniformity of galvanized layer: The galvanized layer should be as uniform as possible to avoid the situation where the local galvanized layer is too thin or too thick to ensure that the entire steel surface can be well protected. If the galvanized layer is uneven, the thin parts are prone to corrosion first, affecting the overall protection effect.
Surface quality: The surface of the galvanized layer should be flat, without obvious defects such as cracks, bubbles, scars, cracks and inclusions. At the same time, for some parts that need to be processed or painted later, the roughness of the galvanized layer surface also needs to meet the relevant requirements to facilitate better combination with subsequent coatings.
3.What are the surface preparation requirements?
Before galvanizing, the steel surface needs to be strictly pretreated to remove impurities such as oil, rust, and scale to ensure that the surface is clean, so that the galvanized layer can be firmly bonded to the substrate. Common pretreatment methods include shot blasting and sand blasting. The surface cleanliness and roughness after treatment must meet the relevant standards. In addition, after galvanizing, some subsequent surface treatments may be carried out as needed, such as passivation and oiling, to further improve its corrosion resistance and surface properties.
4.What are the requirements for dimensional accuracy?
The dimensions of galvanized steel must meet the design requirements, including the thickness, width, length, etc. of the steel plate, as well as the cross-sectional dimensions of the profiles. The dimensional deviation must be within the specified range, for example, the width deviation may be required to be +6mm, etc., to ensure that assembly and other construction operations can be carried out smoothly during the shipbuilding process and that the structural dimensions of the ballast tank meet the design standards.
5.What are the construction process requirements?
During the shipbuilding process, the cutting and welding of galvanized steel also have certain requirements. When cutting, the cut should be as smooth as possible to avoid excessive burrs and slag that affect subsequent processing. When welding, appropriate welding process parameters should be adopted to prevent excessive damage to the galvanized layer due to the influence of welding heat. At the same time, the welding quality should be ensured to avoid welding defects that affect the structural strength. For damaged galvanized layers such as welding parts, repair treatment is usually required to restore their protective properties.