API 570

Covers — The in-service inspection, condition monitoring, rating, repair, and alteration of metallic and FRP piping systems and their associated pressure-relieving devices. Its scope includes:

• Process piping handling hydrocarbons, toxic/flammable chemicals, and high-pressure steam.
• Identification of corrosion mechanisms, determination of corrosion rates, and calculation of remaining life using Condition Monitoring Locations (CMLs).
• Establishment of inspection intervals based on piping classification (Class 1 to 4) tied to the consequence of failure.
• Specialized inspection of high-risk areas like injection points, dead legs, soil-to-air interfaces (SAI), and corrosion under insulation (CUI).

Does NOT cover (exclusions) — the following are governed elsewhere:

• New construction (design and initial fabrication) → ASME B31.3 or the original construction code.
• Heater tubes internal to a fired heater, and boiler internals → specialized API or ASME codes.
• Pipelines regulated under transportation codes → ASME B31.4 / B31.8 and local jurisdictional pipeline rules.
• Detailed theory of damage mechanisms → API RP 571; specific step-by-step inspection practices → API RP 574.

Note on RBI: API 570 explicitly permits and encourages the use of a Risk-Based Inspection (RBI) methodology (per API RP 580/581) to establish inspection intervals, which can override the default fixed maximum intervals prescribed in the code.

API 570 sets highly structured minimum requirements for managing the integrity of in-service piping:

• Program Organization — Requires an owner/user inspection organization. Inspections must be directed by an API 570 Authorized Piping Inspector, while all design and rerating decisions require a Piping Engineer. Personnel must hold specific certifications.
• Piping Classification & Intervals — Piping is categorized into Classes (1 to 4) based on the potential consequence of a leak (e.g., toxicity, flammability). Code defines absolute maximum intervals for thickness and visual inspections based on these classes, though actual intervals are often dictated by the half-life rule (half the remaining life) or RBI.
• Condition Monitoring & CMLs — Mandates the strategic placement of Condition Monitoring Locations (CMLs) to measure wall thickness (typically via UT or RT). The program must account for localized corrosion (pitting) versus general corrosion, and requires specific attention to high-risk zones like injection points and dead legs.
• Repair, Alteration & Welding — Welding for repairs and alterations must strictly follow procedures qualified under ASME Section IX. Nondestructive Examination (NDE) must follow ASME Section V. It outlines acceptable temporary repairs (like clamps or fillet-welded patches) and permanent repairs (like flush insert patches or pipe replacement).
• Rerating — Changing a piping system's design temperature or pressure requires rigorous engineering calculation, updated records, and often a pressure test, ensuring the system meets current construction code requirements for the new conditions.

The technical framework of API 570 is designed to continuously evaluate whether an aging, in-service piping system remains fit for continued safe operation under its design conditions.

Thickness, Corrosion Rate & Remaining Life

The central mathematical mechanism of API 570: actual wall thicknesses measured at CMLs are plotted over time to determine a short-term and long-term corrosion rate. Remaining Life = (Current Actual Thickness − Required Minimum Thickness) ÷ Corrosion Rate. The required minimum thickness is drawn from the original construction code (like ASME B31.3), incorporating pressure design and structural requirements.

Interval Setting & Risk-Based Inspection

Inspection intervals are continuously recalculated. The next thickness inspection is normally set at the lesser of the code-mandated maximum (based on Piping Class) or one-half the calculated Remaining Life. Alternatively, an API 580/581 Risk-Based Inspection (RBI) assessment can be used to scientifically extend or shorten these intervals by evaluating the true probability and consequence of failure.

Fitness-for-Service & Remediation

When significant metal loss, pitting, blistering, or cracking is discovered, API 570 acts as the gateway to a Fitness-For-Service (FFS) assessment per API 579-1/ASME FFS-1. If the FFS evaluation proves the flaw is safe, operation continues. If it fails, API 570 dictates the mandatory repair, component replacement, or derating of the system.

Where to find it in the code: Inspection intervals and classification → Section 6 · Corrosion rate and remaining life → Section 7 · Repairs, alterations, and rerating → Section 8.

Engineering Note: API 570 does not contain its own allowable stress tables or pressure-design formulas. It relies entirely on the original construction code (e.g., ASME B31.3) to provide the engineering baseline. You must use the two codes together to manage an in-service piping system safely.