The weight loss method (defined in ASTM G1 and G31) is the most direct and reliable way to measure uniform corrosion. A metal specimen (coupon) is cleaned, weighed, and exposed to a corrosive environment for a set duration. Afterward, it is cleaned again to remove corrosion products and reweighed. The weight difference directly measures the metal wastage.

This method is considered an absolute baseline because it does not rely on electrical resistance or electrochemical assumptions, which can drift or be affected by noise.

MPY (Mils Per Year) is the industry standard in the US, especially in petroleum engineering. A "mil" is equal to 1/1000th of an inch (0.001 inch). It represents the thickness of metal lost annually.

mm/yr (Millimeters Per Year) is the international metric standard. The conversion is:
• $1 \text{ MPY} = 0.0254 \text{ mm/yr}$
• $1 \text{ mm/yr} \approx 39.37 \text{ MPY}$

An MPY of 1 indicates highly resistant performance, whereas rates exceeding 10 MPY represent aggressive corrosion requiring mitigation.

Uniform corrosion rates assume the weight loss is distributed evenly across the entire surface area. However, aggressive agents (like chlorides) cause localized attack, forming deep pits.

The Pitting Factor (PF) is the ratio of the deepest penetration depth ($d_{max}$) to the average penetration depth ($d_{avg}$) calculated from weight loss:
$$PF = \frac{d_{max}}{d_{avg}}$$

A pitting factor of 1.0 represents perfect uniform corrosion. In untreated cooling water or acidic streams, pitting factors can exceed 5 or 10, meaning a pipe wall will be punctured far earlier than uniform calculations suggest.

In pressure vessel and piping design (ASME Section VIII / B31.3), a specific sacrificial metal thickness is added to the minimum required thickness needed to contain the pressure. This is the Corrosion Allowance.

The theoretical service life is calculated by dividing the available allowance by the calculated corrosion rate:
$$Life = \frac{Allowance}{CR}$$

If the corrosion allowance is 3 mm (118 mils) and the corrosion rate is 5 MPY (0.127 mm/yr), the remaining service life is 23.6 years under uniform thinning.

Like most chemical reactions, corrosion rates increase exponentially with temperature, following an Arrhenius relationship. For typical carbon steel in open systems:
• Kinetic Acceleration: Raising temperature increases the diffusion rate of oxygen and ion mobility, doubling the corrosion rate for every 10°C rise.
• Oxygen Depletion: In open containers, dissolved oxygen solubility drops as water approaches boiling. Since oxygen is required for the cathodic reaction, the corrosion rate peaks around 80°C (176°F) and then decreases.

Fluid velocity accelerates corrosion by increasing mass transfer rates. In many metals (like aluminum, copper, and stainless steels), a protective microscopic oxide layer passivates the surface. When flow exceeds a critical shear velocity, the passive layer is mechanically stripped away.

This combined chemical and mechanical degradation is called Erosion-Corrosion. It is highly localized, commonly occurring at pipe elbows, pump impellers, and valve seats where turbulent impingement is highest.

No. This calculator is strictly for uniform weight loss testing (ASTM G31) and does not model galvanic corrosion.

Galvanic corrosion occurs when two dissimilar metals are in electrical contact within a conductive electrolyte. The anodic metal corrodes rapidly while the cathodic metal is protected. Sizing anode-to-cathode ratio is critical to avoid rapid local failures.

For carbon steels, pH governs oxide stability.
• Acidic (pH < 4): Oxide dissolves. Hydrogen evolution dominates as the cathodic reaction, causing extremely rapid, uniform metal dissolution.
• Neutral/Alkaline (pH 4 to 10): Constant rate, governed by oxygen diffusion.
• Highly Alkaline (pH > 10): Passive oxide film drops the rate close to zero.

Corrosion is electrochemical, consisting of simultaneous anodic and cathodic reactions.
• Anodic reaction (metal oxidation): $Fe \rightarrow Fe^{2+} + 2e^-$
• Cathodic reaction (oxygen reduction): $O_2 + 2H_2O + 4e^- \rightarrow 4OH^-$
The anodic rate is limited by the cathodic oxygen supply. Removing oxygen (boiler deaerators) drops corrosion rates dramatically.

Standard mitigation methods:
• Material Selection: Use stainless steels or nickel alloys instead of carbon steel.
• Barrier Coatings: Epoxies, polyurethanes, or galvanizing.
• Cathodic Protection: Sacrificial zinc/magnesium anodes or Impressed Current (ICCP).
• Chemical Inhibitors: film-forming inhibitors or oxygen scavengers.