What are Static Equipment Inspection Codes?

Pressure vessels, process pipelines, and atmospheric storage tanks are core assets, referred to as static equipment, in refineries, petrochemicals, energy, and chemical plants. During operation, this equipment is subject to degradation mechanisms such as corrosion, erosion, cracking, and material fatigue. API 510, API 570, and API 653, published by the American Petroleum Institute (API), provide a systematic methodology for inspecting, evaluating, and determining inspection periods for this equipment while it is in service.

These three codes are not design codes, but in-service inspection codes: they describe how the integrity of equipment in service should be monitored over time, not the manufacturing rules for new equipment. Their common philosophy is corrosion monitoring based on measurable data (especially thickness measurement), remaining life estimation, and inspection interval planning accordingly.

This page is for informational purposes only regarding the scope and periodic logic of inspection codes. Fitness-for-Service (FFS) and remaining life assessment, as well as weld seam inspection, are separate topics; please refer to the relevant pages for these.

  • API 510 — Pressure vessel operational inspection
  • API 570 — Process pipeline inspection
  • API 653 — Atmospheric storage tank inspection
  • All three are in-service inspection codes, not design/manufacturing codes.

API 510 — Pressure Vessel Inspection Code

API 510 (Pressure Vessel Inspection Code) defines the principles for internal and external inspection, on-stream inspection, and thickness measurement of pressure vessels in operation. The main purpose of the code is to ensure that the vessel remains within safe operating limits by monitoring material loss in the shell and sub-components.

The code defines upper period limits for external visual inspection and internal inspection. Unless justified by Risk-Based Inspection (RBI), the external visual inspection interval for above-ground pressure vessels generally cannot exceed 5 years; the internal or operational inspection interval is determined based on the measured corrosion rate and remaining service life. The corrosion rate is calculated from successive thickness measurements taken over time at the same measurement point.

The RBI approach, as defined in API RP 580, prioritizes inspection scheduling based on risk, which is a combination of the probability and consequences of failure, and may allow intervals beyond predefined limits in justified cases.

  • Scope: internal inspection, external inspection, on-stream inspection, thickness measurement.
  • External visual inspection: Generally a maximum of 5 years unless justified by RBI.
  • Internal/operating system inspection interval: based on corrosion rate and remaining service life.
  • Reference: API RP 580 (Risk-Based Inspection Methodology)

API 570 — Process Pipeline Inspection Code

API 570 (Piping Inspection Code) defines the principles for the inspection, rating, repair, and modification of metallic process pipelines in an enterprise. The code's distinguishing feature is its classification of piping systems into risk classes based on the hazard of the fluid they contain and the service conditions.

Pipelines are generally classified into three categories: Class 1 (highest risk — e.g., flammable/toxic, high-pressure services), Class 2 (medium risk), and Class 3 (low risk, lower-pressure services). Inspection intervals vary according to this classification; for example, in Class 1 lines, thickness measurements and external visual inspections are typically performed at most every 5 years or halfway through the calculated remaining life (whichever is shorter), while intervals may be longer in lower risk classes.

Thickness monitoring is carried out via Thickness Measurement Locations (TMLs) or, in current terminology, Condition Monitoring Locations (CMLs). These points are identified in critical areas where corrosion is expected (elbows, reductions, sections with flow turbulence) and the corrosion rate is determined by repeated measurements over time.

  • Pipe systems are classified into risk categories (Class 1 / 2 / 3)
  • Inspection intervals vary depending on the risk class and remaining lifespan.
  • TML / CML: thickness measurement and condition monitoring points
  • More frequent inspections are expected on Class 1 (high risk) lines.

API 653 — Storage Tank Inspection Code

API 653 (Tank Inspection, Repair, Alteration, and Reconstruction) specifies the principles for operational inspection, repair, alteration, and reconstruction of atmospheric (non-pressurized) above-ground storage tanks. The code focuses on evaluating the integrity of the shell, base, roof, and connecting elements.

Inspection is typically divided into two parts: external and internal inspection. External inspection is usually performed every 5 years at most, depending on the risk or corrosion rate, and includes a visual assessment of elements such as the shell, roof, nozzles, base, and insulation. Internal inspection is usually performed every 10 years at most, or according to corrosion rate calculations; it evaluates the tank base, shell interior, roof structure, and corrosion protection systems.

Since soil-side corrosion on base plates cannot be detected by visual inspection, internal inspection methods such as Magnetic Flux Leakage (MFL) scanning are used. Shell thickness assessment is carried out using ultrasonic testing (UT).

  • Scope: atmospheric above-ground storage tanks (shell, base, roof)
  • External inspection: depending on risk/corrosion, usually every 5 years at most.
  • Internal inspection: typically every 10 years or depending on the corrosion rate.
  • Baseline assessment: MFL scan; shell: ultrasonic thickness measurement.

Common Concepts: Thickness Measurement, Corrosion Rate, and Inspection Interval Logic

The measurement that forms the backbone of all three codes is ultrasonic (UT) monitoring of wall thickness. The difference between two thickness readings taken at different times at the same measurement point is divided by the elapsed time to calculate the corrosion rate (e.g., mm/year). This rate indicates the speed at which the equipment is losing material.

The basic logic behind remaining life calculation is simple: divide the remaining corrosion allowance between the current thickness and the minimum allowable (minimum required) thickness by the corrosion rate. The resulting remaining life determines when the next inspection should be carried out; codes typically limit the inspection interval to the shorter of half the remaining life and the upper limit defined by the code.

This page is limited to the scope and periodization logic of the inspection. Workforce Safety (FFS) analysis, which is an advanced (damage tolerance-based) assessment of whether the remaining thickness is truly sufficient, and the inspection of repair/remodeling welds are separate topics and will be covered on their respective pages.

  • Corrosion rate = difference between consecutive thickness measurements divided by elapsed time
  • Remaining life approximate = remaining corrosion allowance divided by corrosion rate
  • Inspection interval: typically less than half the remaining lifespan and the upper limit of the code.
  • See also: FFS / remaining-life assessment and source inspection (separate pages)

The Concept of Authorized Inspector and its Context in Türkiye

API codes require inspections to be planned and assessed by personnel with Authorized Inspector status certified by API. This is a personnel qualification concept based on API's own Individual Certification Program (ICP) and is not an accreditation granted to a facility or organization.

In Türkiye, the periodic inspection of pressure vessels, storage tanks, and pipelines is mandated by national legislation, not API codes. The relevant framework is the Regulation on Health and Safety Conditions in the Use of Work Equipment (Official Gazette dated 25.04.2013, No. 28628). With the amendment made to this Regulation by the Official Gazette dated 23.12.2025, No. 33116, the term "accredited inspection body" was updated to "equipment inspection body," the principle of preparing reports via the ISG-KATIP system and based on contracts was reinforced, and it was stated that only organizations accredited by TÜRKAK under TS EN ISO/IEC 17020 will be considered equipment inspection bodies, with a transition period foreseen until 1/1/2027 for certain scopes.

In this context, the role of API is complementary: API 510/570/653 does not replace mandatory periodic inspections in Türkiye; however, it provides a reference methodology widely demanded in international projects, export-oriented facilities, and sectors such as refineries and petrochemicals. AES Innovation offers API-referenced technical assessment and information services within the framework of these codes, based on a technical report prepared by a qualified engineer (mechanical engineer).

  • Authorized Inspector: This is API's individual staff certification, not organizational accreditation.
  • Mandatory in Türkiye: Work Equipment Regulation (25.04.2013/28628; amendment 23.12.2025/33116)
  • Changes include: equipment inspection body, mandatory OHS-KATIP certification, TS EN ISO/IEC 17020 and transition to 1/1/2027.
  • API does not replace national periodic inspections; it is a reference methodology for export/refinery projects.
  • AES framework: API-referenced technical evaluation + authorized engineer's technical report.

Information Note

This page is for informational purposes only and does not constitute technical advice, a commitment, or an inspection report. The API inspection intervals and concepts presented are general guidelines, and the actual inspection plan for each piece of equipment will be determined by a qualified engineer (mechanical engineer) on a piece-by-piece basis, taking into account service conditions, historical thickness data, corrosion mechanisms, and applicable legislation. The information on this page does not replace applicable codes and regulations.

AES Innovation conducts work under API 510/570/653 as API-referenced technical assessments and briefings, based on technical reports prepared by authorized engineers. AES does not claim accreditation for these codes; our TÜRKAK accreditation scope is limited only to 6.1 Electrical Installations. Therefore, outputs issued under API codes do not constitute accredited inspection reports. The legal periodic inspection obligations for your equipment in Türkiye must also be fulfilled separately under the Work Equipment Regulation.

  • This content is for informational purposes only; it is not a medical report or technical advice.
  • The equipment-specific plan is determined by the authorized engineer (mechanical engineer).
  • AES's TÜRKAK accreditation is limited to category 6.1 Electrical Installation only.
  • Outputs within the scope of API codes are not accredited inspection reports.

Related Services

Frequently Asked Questions

What are APIs 510, 570, and 653?

These are operational inspection codes published by the American Petroleum Institute (API). API 510 covers pressure vessels, API 570 covers process pipelines, and API 653 covers atmospheric above-ground storage tanks. All three provide a methodology for inspection planning based on thickness monitoring, corrosion rate, and remaining life of equipment in service.

Are API 510/570/653 mandatory in Türkiye?

No. API codes are voluntary standards originating in the US and are not legally mandatory in Türkiye. In Türkiye, periodic inspections of pressure vessels, tanks, and pipelines are mandatory under the Regulation on Health and Safety Conditions in the Use of Work Equipment (amended 25.04.2013/28628 and 23.12.2025/33116). API codes, on the other hand, are a widely requested reference methodology in international, export-oriented, and refinery/petrochemical projects.

Does API inspection replace periodic inspections in Türkiye?

No, it is supplementary. An assessment carried out under API 510/570/653 does not eliminate the mandatory periodic inspection obligation defined in the Work Equipment Regulation. The statutory periodic inspection must also be carried out in accordance with the legislation (including the requirements of the relevant equipment inspection body and the Occupational Safety and Health (OSH)-KATIP system).

How are inspection intervals determined?

Intervals are based on the corrosion rate calculated from thickness measurements taken at the same point over time, and the resulting estimate of remaining life. Codes typically limit the inspection interval to whichever is shorter: half the remaining life plus the upper limit defined by the code. In API 570, the risk class of the piping systems (Class 1/2/3) also affects the interval.

What does Authorized Inspector mean?

This refers to an authorized inspector within the framework of API's Individual Personnel Certification Program (ICP). This is not an accreditation granted to an organization, but rather a personal qualification status. In the context of AES, work is carried out based on a technical report prepared by an authorized engineer (mechanical engineer) as an API-referenced technical assessment.

Does AES conduct this assessment?

AES Innovation provides API-referenced technical assessment and information services under API 510/570/653, based on a technical report prepared by an authorized engineer. However, AES does not claim accreditation for these codes; our TÜRKAK accreditation scope is limited to 6.1 Electrical Installations, and outputs under the API do not constitute accredited inspection reports.