Mastering API 653: A Comprehensive Guide to Tank Inspection and Repair

api
In oil and gas industries, petrochemicals, and storage industries, a significant part of the materials is held in enormous above ground storage tanks (ASTs). The reliability of these tanks is important to minimize loss of product, infliction of harm to the environment and the people and also avoid having to close down for an extended period of time. As for mechanical parameters of ASTs, annual inspection, testing, and maintenance with obligatory repairs of the defined defects are required. It is at this stage where API’s API 653 standard comes in handy. API 653 is the most widely used code for the in-service inspection, repair, alteration, and reconstruction of Aboveground storage tanks. This sets out code and standards that provide tank owners, operators and inspectors with some practices that should be considered for the tanks’ structural integrity and safety during its working years. In this guide, we will provide you with an overview of API 653, what you need to know about the inspection and repair of tankages and the certification of Inspectors as well as the recommended practice. API 653 guidelines are critical for tank safety and compliance irrespective of the role you assume whether you are a tank operator, engineer, or even an API 653 inspector.

Overview of API 653: Purpose and Scope

API 653 was published by the American Petroleum Institute in 1991 under the title, Tank Inspection, Repair, Alteration, and Reconstruction. It was designed to promote a framework that can be used to avoid hazards and guarantee the effective functioning of ASTs, especially those constructed to the API 650 and API 620 specifications.

API 653 is meant to provide guidelines for inspection, repair, alteration, and reconstruction of storage tanks for petroleum products and other materials. The standard covers aspects such as:

  • Setting up of inspection regimes
  • The question of specifying repair practices
  • Procedures for changing tanks with respect to new operational needs
  • Civil work processes for reconstruction or movement of tanks

API 653 applies to ASTs that are:

  • Constructed based on API 650 requirements or other similar standards
  • Employed for the storage of such products as petroleum or any other liquid products.
  • Susceptible to corrosion and fatigue as well as any other phenomenon that weakens the determination of structures.

Key Definitions and Tank Types Covered Under API 653

API 653 applies to various kinds of tanks such as vertical cylindrical tanks and has certain terms used to explain ideas. Some important definitions to understand include:

  • Aboveground Storage Tank (AST): storage tank intended to be placed on the surface of the ground. Petroleum or chemical can be stored in it or any other hazardous liquid can be stored in it.
  • Corrosion Rate: The measure of the rate of material degradation on a surface through chemical or electrochemical processes customarily presented in mils per year (mpy).
  • Minimum Thickness: Minimum required thickness of the tank shell, bottom or roof, as obtained from design calculations to accommodate the internal pressure and other conditions.
  • Inspection Interval: A time interval available between two consecutive inspections of storage tanks based on the findings of a prior inspection and operating conditions of the tanks.

Standalone tanks that hold crude oil, refined petroleum products, chemicals, or even water, are usually as per API 653 under the following conditions, namely, volume capacity and design pressure. These tanks are valuable commodities in the oil and gas industry as well as in the refineries, chemical industry, and other related industries.

Inspection Intervals and Types of Inspections

It is therefore useful to periodically inspect Aboveground Storage Tanks in order to address emergent problems. API 653 mentions various kinds of inspection each of which is carried out at different intervals depending on the status of the tank. The most common inspections are:

  • Routine In-Service Inspections: Conducted routinely (normally on a monthly basis) by operations staff. These inspections are external and are aimed at identifying such basics as leakage or rust issues, and settlement.
  • External Inspections: A survey that is done periodically; every five years to be specific with certified inspectors to examine the condition of the exterior of the tank, shell, roof, as well as foundation. It also has other forms of inspection such as inspecting for corrosion, deformation and signs of building settlement.
  • Internal Inspections: Usually it is necessary each 10 years, but depending on the state of the tank and the rate of corrosion it can be needed more often. During internal inspections the tank is emptied and it is cleaned and its condition on the internal side of the shell as well as on the tank bottom for possible symptoms of corrosion or other structural problems is assessed.
  • Ultrasonic Thickness Testing (UT): A technique applied during both external and internal examination for determining the shell thickness left in the tank. They assist in locating corroded areas and the extent of the corrosion rate within structures; whether structures require repair or not.

These inspections not only inform about the overall condition of the tank, about its remaining useful life, and about the need in repairs or alterations to ensure that the tank will remain safe to operate.

Preparing for an API 653 Inspection

It is important to prepare for an API 653 inspection properly to ensure the best results in the shortest time possible. Before the inspection, several steps should be taken:

  • Tank History Review: Both the tank’s service history and history of inspections, as well as past maintenance and repair documents should be obtained by the inspectors and operators.
  • Cleaning and Ventilation: In the case of internal inspection the tank must first be empty and free of any deposits or any type of sludge. Good flow of air and testing for the type of gases inside the tank is extremely mandatory for the safety of workers inside the tank.
  • Inspection Plan: Create the scheme of inspection where it would be necessary to state a number of aspects Considered aspects: The type and extent of an inspection When, how and by whom The tools and instruments necessary for the operation Inspection of the given item or parts of it
  • Documentation: Make sure that all relevant information such as drawing, design specification and previous inspection reports are on hand for the exercise.

Thus, the examination of thin-walled tanks can be conducted effectively without considerable disruptions of their functioning, and all the essential elements of the tanks can be inspected.

Critical Components of Tank Inspections

During an API 653 inspection, inspectors focus on several critical components of the tank, including:

  • Tank Shell: Every inspector wants to be sure that the shell thickness is uniform and there are no signs of corrosion, pits, bulge or any other sign of damage. They also assess any kind of fixes or changes done on the shell.
  • Tank Bottom: They add that the bottom of the tank is most at risk from corrosion, which may be brought on in part by moisture or chemicals in the ground or within the stored product. Internal inspections look for flow thinning or corrosion of the bottom plates and thickness measurement utilizes ultrasonic testing.
  • Tank Roof: It looks for areas that may develop a rusting process, cracking and overall state showing signs that it is going to leak or fail.
  • Foundations: Any settlement or foundation movement can make the tank or the foundation on which it rests to become weak. Inspectors also assess the tank base for signs of subsidence, movement or crack around the tanks.

Through a keen inspection of these components potential problems can be found before they result in the failure of the tank.

Evaluation of Tank Conditions and Acceptable Limits

As soon as one inspection is over, it is checked, whether the state of the tank corresponds to the acceptable by API 653 limits in regard to some components. Some key evaluation criteria include:

  • Corrosion Rate: The rate is established theoretically using thickness measurements from a previous assessment of the rate of corrosion. When the corrosion rate is too high repairs or alterations may be necessary in order to contain the problem.
  • Minimum Thickness: API 653 has sections that describe the minimum thickness of parts of the storage tank that is allowable. If the shell, roof, or bottom drops lower than these restraints then it is required to be fixed or changed.
  • Settlement: Should there be noticeable movement of the tank foundation it is very likely the tank may need to be supported and this process hinder its movement.

This assessment is used to establish whether or not the tank should be useful for further functioning or whether or not it requires some structural amendments or substitutions for heightened safety.

Repair and Alteration Requirements Under API 653

When a tank inspection indicates that certain repairs or alteration of the tank are required, API 653 gives a recommended approach to it. Repairs may include:

  • Welding of Shell or Bottom: In case of corrosion or damage of the shell or bottom some locations may require the welding of new plates. Welding has to be done by only certified personnel, and this has to be done to API 653 specifications.
  • Replacement of Components: For instance, if the roof is damaged, or the bottom is worn out beyond repair, both may have to be replaced completely.
  • Relining of Tank: Tanks holding corrosive content may require relining of their interior with a corrosion resistant material in order to improve the tanks life.

API 653 also prescribes the standards for modifying a tank to accommodate new operational use, by including expanded capacity, or different content.

Reconstruction and Relocation of Tanks

Rarely, tanks may require reconstruction or may be required to be relocated. API 653 provides information on safe reconstruction of an Ultrasonic tank; how to dismantle and reassemble the various parts; tests that need to be conducted to see if there are traces of leaks and see if the reconstructed container meets the required design and safety standard.

The process of transferring a tank from one location to another is called rerouting, but it is a technical process different from redeployment because rerouting may lead to some harm to the tank and also the efficiency of the tank at the new location is of prior concern. API 653 offers the information on how it is possible to move the tank while being able to uphold the structural stability worth of the tank besides meeting the set industry requirements.

Certification Process for API 653 Inspectors

That is; to become a certified API 653 inspector, one needs to undergo a specific level of education, to have adequate practical experience,and to pass an examination. API 653 certification is intended for people who control the inspection, repair, and maintenance of ASTs. The certification process includes:

  • Education Requirements: API 653, API 650 is mandatory knowledge for the inspector and all the other applicable standards. They should also understand corrosion mechanisms, welding and nondestructive evaluation methods.
  • Experience Requirements: Specific job requirements concerning the educational level vary depending on the candidate, but at least 1-5 years of experience in aboveground storage tanks work is obligatory.
  • Examination: The API 653 examination focuses on understanding of the standard, tanks’ construction, repair methods and ways of inspection.

The persons that get certified are required to take a recertification every three years and they are also supposed to engage in the professional development programs to ensure that they are in touch with the modern trends of the industry.

Best Practices for API 653 Compliance

To ensure compliance with API 653, tank operators and inspectors should follow these best practices:

  • Regular Inspections: Always control the time intervals of inspection as prescribed in API 653 before the failure of tanks occurs.
  • Documentation: All the inspections, repairs and alterations of the tank must be documented for a clear history record of the tank.
  • Qualified Personnel: Various Types of inspections, repairs, and alterations shall be carried out with permission from the correct authorities and performed by skilled staff well conversant with API 653 and other similar standards.
  • Corrosion Control: Interventions like Cathodic protection or internal lining can be employed so as to add up to the duration of the tank.

Thus, the adherence to the best practices pointed out above should make it possible for tank operators to have their aboveground storage tanks work safely and without posing hazards such as failures that would imply high repair costs or leakage problems with environmental consequences.

Conclusion

API 653 is a crucial standard in ensuring that current aboveground storage tanks in industries ranging from oil and gas, chemicals and petrochemicals remain safe, reliable and in compliance. Inspections, careful evaluations, and maintenance of tanks should be performed periodically; tanks can safely perform their intended purpose and protect the environment from failure.

This paper has provided a basic understanding of API 653 and how, when followed to the letter, both inspectors and operators can have confidence that these containers will remain safe to use as well as conform to the legal requirements set and perform effectively as intended until the end of their useful life. API 653 is a certification requirement for the inspectors who are crucial players in the industrial facilities formal rigorous training prepares these professionals with the skills and knowledge required of them to deliver when undertaking their responsibility.

Table of Contents