Q:What principles should be followed in selecting the thickness of the zinc layer of chemical equipment?
A:1. Basic requirements: The average thickness of hot-dip galvanizing is ≥85μm (GB/T 13912), and the thickness can be increased by 20%-50% in special environments.
2. Process selection: Vacuum zinc infiltration is preferred for high temperature or complex structures, and zinc spraying + coating composite protection is used for liquid contact equipment.
3. Verification standard: Pass salt spray test (≥96 hours) and adhesion test to ensure that the quality of the zinc layer meets the requirements of ISO 1461 or ISO 12944.
Q:Regarding the corrosion resistance requirements of chemical equipment, what are the industry standards for selecting the thickness of the zinc layer?
A:National Standard (GB/T 13912-2020)
Non-centrifugal parts with steel thickness ＞6mm: local thickness ≥70μm, average thickness ≥85μm.
Castings or centrifugally treated parts: local thickness ≥40μm, average thickness ≥50μm (applicable to threaded parts, etc.).
Highly corrosive environment (such as chemical industry zone): The zinc layer thickness needs to be increased by 20%-30% on this basis.
International standard (ISO 1461:2022)
General chemical environment: When the steel thickness is greater than 6mm, the average zinc layer thickness is ≥85μm, and the local thickness is ≥70μm 12.
Special materials (such as ultra-low reaction steel): A higher thickness requirement must be followed.
Q:How to choose the thickness of zinc layer for chemical equipment according to different corrosion environments?
A:High corrosion: industrial atmosphere, moderate salt spray, hot-dip galvanizing with slight acid and alkali vapor ≥85μm, electroplating ≥20μm.
Very high industrial: strong acid/alkali mist, high humidity, strong sulfide pollution hot-dip galvanizing ≥100μm, or vacuum zincizing 100-120μm.
Very high marine: coastal high salt spray, ship deck, offshore platform hot-dip galvanizing ≥120μm, or zinc-aluminum alloy coating.
Q:How to choose the zinc layer in special scenarios?
A:1. High temperature environment (such as reactors, pipelines)
Recommended process: vacuum zinc infiltration (zinc layer thickness 100-120μm), the zinc-iron alloy layer remains stable at 600℃, avoiding oxidation and peeling of the zinc layer at high temperature.
2. Liquid contact equipment (such as storage tanks, reactors)
Inner wall protection: zinc spraying layer thickness 100-150μm, combined with electrostatic conductive coating (total thickness ≥400μm), can resist strong acid/alkali liquid corrosion.
Bottom plate protection: zinc layer thickness must be ≥350μm, and sacrificial anode protection is required.
3. High-strength steel or complex structural parts
Recommended process: vacuum zinc infiltration (thickness 20-120μm), due to its diffusion metallurgical bonding characteristics, it can avoid the problem of hot-dip galvanizing coating peeling, while improving the surface hardness (HV400 or above).
Q:What are the alternatives for corrosion resistance in the chemical industry?
A:Galvalume:
Zinc-aluminum-silicon alloy coating (55% aluminum, 43.4% zinc, 1.6% silicon), corrosion resistance is 2-4 times that of pure zinc, especially suitable for high temperature (≤315°C) and sulfur-containing environment (such as petrochemical equipment).
Composite coating (galvanizing + spraying):
Spraying anti-corrosion coatings such as epoxy and polyurethane on the hot-dip galvanized layer can significantly extend the service life (such as offshore platform equipment).
Regular maintenance:
Check the integrity of the coating and use zinc-based repair paint (such as cold-dip galvanizing paint) to repair local damage in time.