Full Comparison & Selection Guide For Four Surface Treatment Crafts Of Grade 4.8/8.8/10.9/12.9 High-strength Bolts

Full Comparison & Selection Guide For Four Surface Treatment Crafts Of Grade 4.8/8.8/10.9/12.9 High-strength bolts

High-strength bolts obtain high tensile strength via quenching & tempering heat treatment, higher hardness brings stronger hydrogen absorption sensitivity. Wrong electroplating coating easily triggers delayed hydrogen embrittlement fracture and serious equipment safety accidents. Zhuhai Jiali Heavy Industry divides four standardized anti-corrosion solutions for different tensile grades and outdoor corrosion environments, matches coatings for dry indoor, riverside inland, coastal tidal flat and offshore extreme corrosion scenarios to avoid mass failure caused by material selection mistakes.

1. Core Parameter Comparison Table Of Four Mainstream Anti-corrosion Coatings For High-strength Bolts

Surface Treatment Craft	Hydrogen Embrittlement Risk Level	Standard Neutral Salt Spray Hours	Max Long-term Operating Temp	Applicable Bolt Tensile Grade	Relative Cost Increase
Standard Electro Galvanizing	Extremely High Risk	500h no red rust	120℃	Grade4.8/8.8 only, forbidden for 10.9/12.9	Base reference price
Zinc-Nickel Alloy Electroplating	Medium Risk, mandatory dehydrogenation baking	1500h no red rust	160℃	All grades, first choice for wind & energy storage	+35%
Dacromet Mechanical Coating	Ultra-low risk, barely no hydrogen absorption	1000h no red rust	220℃	All grades, suitable for high temp boilers & construction machinery	+60%
Mechanical Hot Galvanizing	Low risk, no strong acid pickling process	2000h no red rust	250℃	Grade8.8/10.9, offshore heavy steel structure	+110%

2. Mandatory Coating Selection Standard For Four Industrial Scenarios

1. Dry indoor workshop & general machinery (Grade4.8/8.8): 5μm standard electro galvanizing, lowest cost without high chloride corrosion risk; 2. Onshore wind power & inland energy storage containers (Grade10.9/12.9): 10μm zinc-nickel coating, hold 6h at 220℃ for dehydrogenation within 2h after plating; 3. Riverside lakeside construction machinery & high temp boiler equipment: Dacromet coating, zero hydrogen embrittlement worry, stable under long-term 180℃ working condition; 4. Coastal & offshore wind heavy flange bolts: Thickened mechanical hot galvanizing coating to resist high salt mist seawater corrosion, match grade10.9 heavy load structure.

3. Coating Processing & Storage Failure Prevention Control Key Points

1. Time limit rule for Grade10.9/12.9 plated bolts: All plated goods must enter oven within 3 hours for dehydrogenation, delayed treatment leads hydrogen deep into lattice which cannot be fully removed; 2. Dacromet matching taboo: Do not assemble with stainless steel gaskets, galvanic corrosion accelerates coating peeling; 3. Thread control for hot galvanized bolts: Re-tap threads after hot galvanizing to avoid over-thick coating causing over-torque and permanent seizure; 4. Separated finished goods storage: Store different coating bolts in independent warehouses, seal galvanized goods for moisture-proof, prevent hard scratch damage on Dacromet anti-corrosion film.

Full Comparison & Selection Guide For Four Surface Treatment Crafts Of Grade 4.8/8.8/10.9/12.9 High-strength Bolts