What Is API 570? Piping Inspection Code

API 570 (Piping Inspection Code: In-Service Inspection, Rating, Repair, and Alteration of Piping Systems) is a post-construction inspection standard published by the American Petroleum Institute. It provides minimum requirements for inspecting metallic and fiberglass-reinforced plastic piping systems that are already in service at petroleum refineries, chemical plants, and other process facilities.

While ASME B31.3 governs new construction, API 570 takes over once the piping system enters operation.

Scope

Covered	Not Covered
In-service metallic process piping	New construction (ASME B31.3)
Piping in refineries, chemical plants, and process facilities	Cross-country pipelines (API 1160, ASME B31.4/B31.8)
Piping connected to pressure vessels, tanks, and equipment	Non-metallic piping (except FRP per Appendix)
Repairs, alterations, and rerating of existing piping	Plumbing, HVAC, or building services piping

Inspection Classification

API 570 classifies piping circuits based on consequence of failure and likelihood of failure (risk):

Class	Description	Max Inspection Interval
Class 1	Highest risk: services that could result in an immediate emergency (toxic, flammable, high-energy)	5 years (external), 5 years (thickness measurement)
Class 2	Medium risk: flammable or toxic services with moderate consequence	5 years (external), 5 years (thickness)
Class 3	Lower risk: services with limited consequence of failure	10 years (external), 10 years (thickness)

The owner/operator may adjust intervals based on risk-based inspection (RBI) methodologies per API 580/581, provided the overall risk is managed.

Key Inspection Activities

Activity	Method	Purpose
Thickness measurement	Ultrasonic testing (UT)	Determine remaining wall; calculate corrosion rate
Visual examination	Direct or remote	Identify external corrosion, insulation damage, support issues
Corrosion under insulation (CUI)	UT, profile radiography, or insulation removal	Detect hidden corrosion on insulated piping
Small-bore piping	Visual + vibration assessment	Identify vibration fatigue and socket weld cracking
Injection point inspection	UT + internal visual or RT	Detect localized thinning at chemical injection points
Deadleg inspection	UT	Identify internal corrosion in stagnant sections

Corrosion Rate and Remaining Life

API 570 requires calculation of two values:

• Short-term corrosion rate: Based on the two most recent thickness readings
• Long-term corrosion rate: Based on original (or earliest available) and most recent thickness readings

The higher of the two rates is used to calculate:

Remaining Life = (t_actual - t_required) / corrosion rate

Where t_required is the minimum thickness per ASME B31.3 for the design conditions.

Common Mistake

Using only the long-term corrosion rate when a process change has recently accelerated corrosion. Always compare short-term and long-term rates. A sudden increase in short-term rate signals a change in corrosion mechanism that demands immediate engineering review.

Fitness-for-Service

When a piping circuit falls below minimum code thickness, API 570 references API 579-1/ASME FFS-1 (Fitness-For-Service) for detailed engineering assessment. FFS evaluation may demonstrate that the piping is still safe to operate under specific conditions, avoiding immediate replacement.

API 570 Certification

API offers an individual certification examination (API 570 Piping Inspector) that validates knowledge of the code, ASME B31.3, welding inspection, NDE methods, and corrosion assessment. Many owner/operators and inspection companies require this certification for piping inspectors working in process plants.

Read the full guide to LEL/UEL and flammable gas safety