Manufacturers of composite steel formwork: How to evaluate the corrosion rate of the formwork?

1、 Basic quantitative detection methods
Weight method
Weight loss method: measure mass loss after removing corrosion products, suitable for scenarios where corrosion products are prone to detachment
Formula:
V
=
W
0
−
W
one
S
⋅
T
V=S ⋅ TW0 − W1 (unit: g/(m ² · h))
Weight gain method: retaining the weight of corrosion products for use in dense oxide film scenarios
Depth indicator conversion
Convert quality loss into thickness loss by combining density (ρ)
Formula:
D
=
V
×
eight point seven six
ρ
D=ρ V × 8.76 (unit: mm/a)
Example: Carbon steel (ρ=7.85g/cm ³) has a mass loss of 1g/m ² · h, corresponding to an annual corrosion depth of 0.11mm4
2、 Electrochemical rapid assessment
Applicable scenarios for core parameters of the method
Polarization curve method for corrosion current density
i
c
o
r
r
i 
corr
Research on the Corrosion Mechanism of Laboratory Media
Electrochemical Impedance Spectroscopy (EIS) Charge Transfer Resistance
R
c
t
R 
ct
Coating/plating failure analysis
Linear polarization method polarization resistance
R
p
R 
p
On site rapid detection (error ± 15%)
3、 Special testing for localized corrosion
Pitting evaluation
Chemical soaking method: Soak in ferric chloride solution (50g/L FeCl ∝· 6H ₂ O) at 35 ℃ for 24 hours
Evaluation criteria: maximum pit depth/density
Critical pitting temperature (CPT): The maximum temperature at which a material can withstand pitting corrosion is determined by a potential jump
Stress Corrosion Testing
Constant load method: Apply a continuous load of 80% yield strength
Medium selection: 42% MgCl ₂ boiling solution (155 ℃)
4、 Coupling analysis of environmental parameters
Corrosion factor monitoring
Influence mechanism of parameter sensor type
For every 100ppm increase in chloride ion concentration and ion selective electrode, the corrosion rate of stainless steel increases by 35%
Electrochemical corrosion significantly intensifies when relative humidity capacitive sensor RH>60%
Accelerated Test Simulation
Cyclic corrosion test: including three-stage cycles of salt spray (5% NaCl), drying (40 ℃/30% RH), and wetting (98% RH)
High temperature and high-pressure reactor test: simulating the working conditions of oil and gas pipelines (150 ℃/10MPa H ₂ S environment)
5、 Engineering Application Standards
Data criteria
Uniform corrosion: graded according to GB/T 15957-2025 (Grade I<0.01mm/a, Grade IV>0.5mm/a)
Localized corrosion: Comparison of pitting corrosion grade maps specified in ASTM G46-2024
Report elements
Required data: initial/termination weight, exposed area, time, environmental parameters (T/RH/Cl ⁻)
Corrosion morphology description: SEM micrograph+energy dispersive spectroscopy (EDS) analysis
By combining multiple methods for verification (such as weight method+electrochemical+microscopic analysis), it can be ensured that the corrosion rate assessment error is controlled within ± 8%