Pressure Vessel Inspection Code In service Inspection, Rating, Repair, and Alteration API 510 TENTH EDITION, MAY 2014 ADDENDUM, MAY 2017 Special Notes API publications necessarily address problems of[.]
General Application
This inspection code governs the in-service inspection, repair, alteration, and rerating of pressure vessels and their associated pressure-relieving devices It is applicable to all hydrocarbon and chemical process vessels that are in service, unless explicitly excluded, and may also be extended to process vessels in other industries at the discretion of the owner/user This includes vessels built according to relevant construction codes, such as the ASME Boiler and Pressure Vessel Code.
There are several categories of vessels based on their construction standards: a) vessels built according to the ASME Code; b) noncode vessels, which are not fabricated to any recognized construction code and do not meet established standards; c) jurisdictional special vessels, which are constructed and approved based on specific design, fabrication, inspection, testing, and installation accepted by the jurisdiction; and d) nonstandard vessels, which are made to a recognized construction code but have lost their nameplate or stamping.
Vessels that have been officially retired and abandoned are no longer considered financial assets and thus fall outside the scope of the "in-service inspection" code.
The ASME Code and other recognized construction codes primarily focus on new construction; however, their technical requirements for design, welding, non-destructive examination (NDE), and materials are also applicable to the inspection, rerating, repair, and alteration of in-service pressure vessels In cases where an in-service item cannot adhere to the construction code due to its orientation towards new construction, the standards for design, material, fabrication, and inspection must align with API 510 instead When in-service vessels are subject to both the construction code and API 510, or if conflicts arise, API 510's requirements will take precedence Notably, API 510 uses the term "applicable requirements of the construction code" to emphasize its intent, rather than stating "in accordance with the construction code."
This inspection code is applicable solely to owner/users who engage or have access to technically qualified personnel and organizations, including an authorized inspection agency, a repair organization, an engineer, an inspector, and examiners.
Inspectors must obtain certification as outlined in the inspection code (refer to Annex B) While existing codes address various industries and general service applications (such as NB-23), the refining and petrochemical sector has created this specific inspection code to meet its unique needs for vessels and pressure-relieving devices, adhering to the defined scope limitations.
This code outlines the necessary in-service inspection and condition-monitoring program to assess the integrity of pressure vessels and pressure-relieving devices It aims to deliver accurate and timely evaluations to identify any condition changes that may jeopardize safe operation Owners and users are required to take corrective actions based on inspection results to ensure the ongoing safety of these pressure systems.
The adoption of this inspection code must align with existing regulatory requirements; however, if this code imposes stricter standards than those regulations, its requirements will take precedence.
Specific Applications
All pressure vessels utilized in exploration and production (E&P) services, including drilling, production, gathering, transportation, lease processing, and treatment of liquid petroleum, natural gas, and associated brine, are subject to inspection under the alternative rules outlined in Section 9 With the exception of Section 6, the entire inspection code applies to these pressure vessels The alternative rules in Section 9 cater to services regulated by various authorities, including the U.S Coast Guard, the Office of Hazardous Materials Transportation of the U.S Department of Transportation, the Bureau of Ocean Energy Management, and state and local oil and gas agencies, ensuring compliance with safety, spill, emission, and transportation controls.
Certain vessels are exempt from the specific requirements of this inspection code, as detailed in Annex A Nevertheless, owners and users have the flexibility to incorporate any excluded pressure vessel into their inspection program in accordance with this code.
Certain vessels that meet the criteria outlined in ASME Code, Section VIII, Division 1 may be exempted but should still be evaluated for inclusion based on risk factors, including the likelihood and impact of failure, as assessed by the owner or user For instance, vacuum flashers used in refining processes or other significant vessels operating under vacuum conditions are examples of such equipment.
Recognized Technical Concepts
The inspection code for in-service pressure vessels emphasizes the importance of Fitness-For-Service (FFS) assessments and risk-based inspection (RBI) methodologies Detailed procedures for assessing specific damage types are outlined in API 579-1/ASME FFS-1 Additionally, API 580 offers guidelines for implementing a risk-based assessment program, while API 581 provides a method for conducting RBI based on the principles established in API 580.
The documents referenced herein are essential for the application of this document For references with specific dates, only the cited edition is applicable In the case of undated references, the most recent edition of the referenced document, including any amendments, is relevant.
API 510 Inspector Certification Examination Body of Knowledge
API Recommended Practice 571, Damage Mechanisms Affecting Fixed Equipment in the Refining Industry
API Recommended Practice 572, Inspection of Pressure Vessels
API Recommended Practice 576, Inspection of Pressure-relieving Devices
API Recommended Practice 577, Welding Inspection and Metallurgy
API Recommended Practice 578, Material Verification Program for New and Existing Alloy Piping Systems
API Standard 579-1/ASME FFS-1, Fitness-For-Service
API Recommended Practice 580, Risk-Based Inspection
API Recommended Practice 581, Risk-Based Inspection Methodology
API Recommended Practice 582, Welding Guidelines for the Chemical, Oil, and Gas Industries
API Recommended Practice 583, Corrosion Under Insulation and Fireproofing
API Recommended Practice 584, Integrity Operating Windows
API Recommended Practice 585, Pressure Equipment Integrity Incident Investigations
API Recommended Practice 939-C, Guidelines for Avoiding Sulfidation (Sulfidic) Corrosion Failures in Oil Refineries
API Recommended Practice 941, Steels for Hydrogen Service at Elevated Temperatures and Pressures in Petroleum
API Recommended Practice 2201, Safe Hot Tapping Practices for the Petroleum and Petrochemical Industries ASME PCC-1 1 , Guidelines for Pressure Boundary Bolted Flange Joint Assembly
ASME PCC-2, Repair of Pressure Equipment and Piping
ASME Boiler and Pressure Vessel Code, Section II: Materials
ASME Boiler and Pressure Vessel Code, Section V: Nondestructive Examination
ASME Boiler and Pressure Vessel Code, Section VIII: Rules for Construction of Pressure Vessels; Division 1
ASME Boiler and Pressure Vessel Code, Section VIII: Rules for Construction of Pressure Vessels; Division 2: Alternative Rules
ASME Boiler and Pressure Vessel Code, Section IX: Welding and Brazing Qualifications
ASNT CP-189 2 , Standard for Qualification and Certification of Nondestructive Testing Personnel
ASNT SNT-TC-1A, Personnel Qualification and Certification in Nondestructive Testing
NACE MR0103 3 , Materials Resistant to Sulfide Stress Cracking in Corrosive Petroleum Refining Environments
1 ASME International, 3 Park Avenue, New York, New York 10016-5990, www.asme.org.
2 American Society for Nondestructive Testing, 1711 Arlingate Lane, P.O Box 28518, Columbus, Ohio 43228, www.asnt.org.
3 NACE International (formerly the National Association of Corrosion Engineers), 1440 South Creek Drive, Houston, Texas 77218-8340, www.nace.org.
NACE SP0170, Protection of Austenitic Stainless Steels and Other Austenitic Alloys from Polythionic Acid Stress
Corrosion Cracking During Shutdown of Refinery Equipment
NACE SP0472, Methods and Controls to Prevent In-service Environmental Cracking of Carbon Steel Weldments in
National Board NB-23 4 , National Board Inspection Code
OSHA 29 CFR Part 1910 5 , Occupational Safety and Health Standards
WRC Bulletin 412 6 , Challenges and Solutions in Repair Welding for Power and Processing Plants
3 Terms, Definitions, Acronyms, and Abbreviations
Terms and Definitions
For the purposes of this code, the following terms and definitions apply.
A physical change in a component that impacts the pressure-holding capacity of a pressure vessel must be carefully evaluated, as it may exceed the parameters outlined in existing data reports However, certain modifications should not be classified as alterations; these include comparable or duplicate replacements, the addition of reinforced nozzles that are equal to or smaller than the existing ones, and the installation of nozzles that do not necessitate reinforcement.
The pressure vessel must be constructed in accordance with recognized engineering standards or practices, as determined by the owner, user, or engineer, to ensure its suitability for the specific application.
Approval/agreement to perform a specific activity (e.g repair) prior to the activity being performed.
Pressure vessel inspections can be conducted by various organizations, including: a) the jurisdiction's inspection organization where the vessel is utilized; b) an insurance company's inspection organization that is licensed to provide pressure vessel insurance; c) an owner's or user's inspection organization that focuses solely on their own equipment; or d) an independent organization or individual contracted by the owner/user, provided they are recognized by the relevant jurisdiction It is essential for the owner/user's inspection program to implement necessary controls when utilizing contract inspectors.
4 The National Board of Boiler and Pressure Vessel Inspectors, 1055 Crupper Avenue, Columbus, Ohio 43229, www.nationalboard.org.
5 Occupational Safety and Health Administration, 200 Constitution Avenue, NW, Washington, DC 20210, www.osha.gov.
6 Welding Research Council, P.O Box 201547, Shaker Heights, Ohio 44120, www.forengineers.org.
An inspector, as defined in API 510, is a qualified and certified employee of an authorized inspection agency responsible for conducting inspections in accordance with the inspection code, including Annex B.
Designated areas on pressure vessels, known as Corrosion Monitoring Locations (CMLs), are crucial for conducting periodic external examinations to assess the vessel's condition These CMLs may include multiple examination points and employ various inspection techniques tailored to the anticipated damage mechanisms, ensuring a high probability of detection A CML can be as small as a 2-inch diameter spot or a plane section of a nozzle, where recording points are strategically placed in all four quadrants.
NOTE CMLs now include but are not limited to what were previously called TMLs.
The original construction code of a vessel, which may include outdated standards like API/ASME, ASME Code, or state-specific regulations, plays a crucial role in determining its design and safety compliance.
Welding techniques aimed at achieving controlled grain refinement and tempering in the heat-affected zone of the base metal include various controlled-deposition methods Notable techniques are temper bead, which tempers the layer beneath the current bead, and half bead, which involves removing half of the initial layer For more details, refer to section 8.1.7.4.3.
Additional material thickness available to allow for metal loss during the service life of the vessel component.
The rate of metal loss due to erosion, erosion/corrosion, or the chemical reaction(s) with the environment, either internal and/or external.
A person, acceptable to the owner/user, who has knowledge and experience in corrosion damage mechanisms, metallurgy, materials selection, and corrosion monitoring techniques.
Refers to all forms of CUI including stress corrosion cracking and corrosion under fireproofing.
Cyclic loading from pressure, thermal, and mechanical sources can lead to fatigue damage in service conditions Additional cyclic loads may result from vibrations caused by impacts, turbulent flow vortices, compressor resonance, wind, or their combinations Examples of vessels experiencing cyclic service include coke drums, mole sieves, and pressure swing adsorbers.
Deterioration in the refining and chemical process industry can lead to flaws and defects that compromise the integrity of vessels Common issues include corrosion, cracking, erosion, and dents, along with other mechanical, physical, or chemical impacts For a detailed overview of these damage mechanisms, refer to API 571.
An imperfection whose type or size exceeds the applicable acceptance criteria and is therefore rejectable.
The temperature used for the design of the pressure vessel per the applicable construction code.
Records detailing vessel design, personnel training, inspection plans, and results are essential for maintaining vessel integrity and reliability This includes documentation of non-destructive examination (NDE), repair, alteration, rerating, and pressure testing activities, as well as fitness-for-service (FFS) assessments and the procedures for conducting these tasks.
3.1.19 examination point recording point measurement point test point [test point is a term no longer in use as test refers to mechanical or physical tests (e.g tensile tests or pressure tests)]
A CML (Condition Monitoring Location) for pressure vessels is defined by a circular area with a diameter not exceeding 3 inches (75 mm) These CMLs can encompass several examination points; for instance, a vessel nozzle can serve as a CML and include multiple examination points located in each of the four quadrants around the nozzle.
Quality control (QC) functions performed by examiners (e.g NDEs in accordance with approved NDE procedures).
An individual supporting the inspector conducts specific non-destructive examinations (NDE) on pressure vessel components and assesses them against the relevant acceptance criteria However, they do not interpret the examination results according to API 510 unless they have received specific training and authorization from the owner or user.
A visual inspection of a pressure vessel is conducted externally to identify any conditions that may affect its pressure integrity or compromise the integrity of supporting structures such as ladders, platforms, and supports This inspection can take place while the vessel is in operation or when it is out of service, and it may be performed concurrently with an on-stream inspection.
Fitness-For-Service (FFS) evaluation
A methodology whereby flaws and other deterioration/damage or operating conditions contained within a pressure vessel are assessed in order to determine the integrity of the vessel for continued service.
Corrosion that is distributed more or less uniformly over the surface of the metal, as opposed to localized corrosion.
The portion of the base metal whose mechanical properties or microstructure have been altered by the heat of welding or thermal cutting.
A point in the repair or alteration process beyond which work may not proceed until the required inspection or NDE has been performed.
Flaws or other discontinuities noted during inspection or examination that may or may not exceed the applicable acceptance criteria.
A response or evidence resulting from the application of a NDE that may be nonrelevant or could be flaws or defects upon further analysis.
3.1.29 industry-qualified ultrasonic angle beam examiner
A person who possesses an ultrasonic (UT) angle beam qualification from API (e.g API QUTE/QUSE Detection and Sizing Tests) or an equivalent qualification approved by the owner/user
NOTE Rules for equivalency are defined on the API ICP website.
A pressure vessel is classified as "in service" once it has been operational, distinguishing it from newly constructed vessels that have yet to be utilized or those that have been retired Notably, even if a pressure vessel is temporarily out of operation due to a process outage, it remains categorized as an in-service pressure vessel.
Pressure vessels that are excluded from this discussion are those still under construction or in transit to the site before being put into service, as well as those that have been retired However, it does encompass pressure vessels that are temporarily out of service yet remain at their operational location This refers to a specific phase in the service life of a vessel, occurring between its installation and its removal from service.
All inspection activities associated with a pressure vessel once it has been placed in service but before it is permanently retired from service.
Acronyms and Abbreviations
For the purposes of this code, the following acronyms and abbreviations apply.
ASME Code ASME Boiler and Pressure Vessel Code, including its addenda and code cases
GMAW gas metal arc welding
GTAW gas tungsten arc welding
MAWP maximum allowable working pressure
MDMT minimum design metal temperature
SMAW shielded metal arc welding
Owner/User Organization Responsibilities
Owners and users of pressure vessels must manage the inspection program for both the vessels and their pressure relief devices, ensuring compliance with established inspection frequencies and maintenance requirements They are also responsible for the oversight of an authorized inspection agency as outlined in the relevant code Additionally, the owner/user inspection organization is tasked with overseeing activities related to the rating, repair, alteration, and engineering assessments of their pressure vessels and relief devices.
4.1.2 Owner/User Systems and Procedures
An owner/user organization must establish a comprehensive quality assurance (QA) inspection and repair management system for pressure vessels and pressure-relieving devices, ensuring compliance with inspection codes This system should include a clear organizational structure for inspection personnel, thorough documentation of inspection and QA procedures, and detailed reporting of inspection and test results Additionally, it is essential to develop risk-based inspection plans, establish appropriate inspection intervals, and implement corrective actions based on inspection outcomes Internal audits must be conducted to ensure adherence to the QA manual, while all drawings, calculations, and specifications for repairs must undergo review and approval The organization must continuously meet jurisdictional requirements and report any process changes affecting vessel integrity Training for inspection personnel on tools and techniques is crucial, as is ensuring that only qualified welders and NDE personnel are utilized All repairs must comply with the inspection code, and materials used must conform to applicable construction codes Proper maintenance and calibration of inspection equipment are necessary, along with ensuring that contract inspection organizations meet the same standards Finally, internal audits for the QC system of pressure-relieving devices and controls to verify inspectors' visual acuity are vital for maintaining inspection integrity.
Management must implement a clear requirement and process to guarantee that inspectors undergo an annual vision test This test is essential to confirm their ability to read standard J-1 letters on Jaeger test charts for near vision.
The owner or user must implement a robust Management of Change (MOC) process to effectively review and control modifications to both the process and hardware A well-executed MOC review is crucial for the success of any pressure vessel integrity management program, as it enables the inspection team to maintain safety and compliance.
1) to be able to address issues concerning the adequacy of the pressure equipment design and current condition for the proposed changes,
2) to anticipate changes in corrosion or other types of damage, and
3) to update the inspection plan and records to account for those changes
The Management of Change (MOC) process is crucial when the integrity of pressure equipment is at risk, necessitating the involvement of inspection, materials/corrosion, and mechanical engineering expertise to identify design issues and predict the impact of changes on pressure vessel integrity The inspection team must participate in the approval process for any modifications that could compromise this integrity Additionally, all hardware and process changes should be incorporated into the MOC process to maintain its effectiveness.
To ensure the integrity of pressure equipment, it is crucial for owners and users to implement and maintain a robust program for creating and monitoring integrity operating windows (IOWs) IOWs help prevent exceedances of process parameters that could adversely affect equipment integrity Historically, future inspection plans and intervals have relied on previous corrosion rates linked to past operating conditions Without a solid IOW and process control program, there may be no early warning of changing conditions that could compromise equipment integrity or validate the current inspection strategy Any deviations from established IOW limits should be promptly reported to inspection and engineering teams, enabling them to adjust or develop new inspection plans based on the severity of the exceedance.
Establishing Integrity Operating Windows (IOWs) for critical process parameters is essential to maintain equipment integrity Key parameters include temperatures, pressures, fluid velocities, pH levels, flow rates, chemical injection rates, and the presence of corrosive constituents IOWs should define both upper and lower limits for these parameters as necessary It is crucial to closely monitor IOWs during start-ups, shutdowns, and significant process disturbances to ensure safe operations.
584 for more information on issues that may assist in the development of an IOW program.
Engineer
The pressure vessel engineer is accountable to the owner or user for the design, engineering review, analysis, and evaluation of pressure vessels and pressure-relieving devices, as outlined in the inspection code.
Repair Organization
Repairs and alterations must be conducted by a qualified repair organization, which is accountable to the owner or user This organization is responsible for supplying the necessary materials, equipment, quality control, and workmanship to ensure the vessel or pressure-relieving device is maintained and repaired according to the inspection code requirements For further details, refer to the definition of a repair organization in section 3.1.62.
Inspector
The inspector is accountable to the owner/user for ensuring that inspection, non-destructive examination (NDE), repairs, and pressure testing comply with API 510 code requirements Direct involvement in inspection activities, particularly visual inspections, is essential, often necessitating fieldwork to adhere to procedures and inspection plans While the inspector may receive assistance from qualified individuals, all NDE results must be evaluated and approved by the inspector, who will then provide recommendations for repairs, replacements, or continued service fitness Inspectors must be certified per Annex B provisions and can be either employees of the owner/user or acceptable contractors.
Examiners
4.5.1 The examiner shall perform the NDE in accordance with job requirements, NDE procedures, and owner/user specifications.
The examiner is not required to hold API 510 inspector certification or be an employee of the owner/user; however, they must be trained and competent in the non-destructive examination (NDE) procedures utilized The owner/user may mandate proof of this competency through relevant certifications, such as ASNT SNT-TC-1A, ASNT CP-189, CGSB, and AWS QC1 Additionally, inspectors performing their own examinations using NDE techniques must meet the qualifications set forth by the owner/user.
The examiner's employer must keep certification records for all employed examiners, detailing their qualifications, dates, and results These records should be accessible to the inspector responsible for ensuring that all NDE examiners are adequately qualified for their tasks, thereby assuring compliance for the owner/user.
Other Personnel
Personnel with specialized knowledge regarding pressure vessels must promptly inform inspectors or engineers of any potential issues affecting vessel integrity This includes actions requiring Management of Change (MOC), operations outside the defined Integrity Operating Window (IOW), changes in feedstock sources that may increase corrosion rates or introduce new damage mechanisms, and any vessel failures or repairs along with failure analysis reports Additionally, they should report on cleaning and maintenance procedures that could impact vessel integrity, share experiences from other plants regarding similar failures, and notify about unusual conditions such as noises, leaks, vibrations, or deterioration of the vessel and its support structure Lastly, any engineering evaluations, including Fitness-for-Service (FFS) assessments, that necessitate actions to maintain mechanical integrity until the next inspection should also be communicated.
Inspection Organization Audits
Periodic audits of each owner/user organization are essential to ensure that the authorized inspection agency complies with the inspection code requirements The audit team should comprise experienced professionals, ideally from another owner/user site, central office, or a qualified third-party organization specializing in refining and petrochemical inspection programs Additionally, it is advisable for the site inspection organization to conduct self-audits regularly.
The audit team must assess whether the inspection code's requirements and principles are fulfilled, ensure that owner/user responsibilities are effectively managed, verify the existence of documented inspection plans for pressure vessels, and confirm that inspection intervals and extents are sufficient Additionally, they should evaluate the application of various inspection types and surveillance, ensure the adequacy of inspection data analysis and recording, and check that repairs, reratings, alterations, and engineering assessments adhere to the code.
The audit team must provide the owner or user with a report detailing their findings In cases of nonconformance, the authorized inspection agency is responsible for implementing corrective actions It is essential for each organization to develop a system to track and ensure the completion of these corrective actions stemming from audit findings Additionally, the resolutions to the audit findings should be accessible for the audit team's review and should be evaluated in future audits.
5 Inspection, Examination, and Pressure Testing Practices
Inspection Plans
An inspection plan shall be established for all pressure vessels and pressure-relieving devices within the scope of this code.
5.1.2 Development of an Inspection Plan
The inspection plan must be created by the inspector and/or engineer, with consultation from a corrosion specialist as necessary to identify potential damage mechanisms and specific locations where these mechanisms may arise Refer to section 5.4.1 for further details.
The inspection plan is formulated by analyzing various data sources, focusing on current or potential damage mechanisms It is essential to assess the methods and extent of Non-Destructive Examination (NDE) to ensure they effectively identify the damage mechanisms and their severity Scheduled examinations should consider factors such as the type and rate of damage progression, equipment tolerance, the reliability of NDE methods, maximum intervals set by codes and standards, previous examination results, recent operating history including IOW exceedances, MOC records affecting inspection plans, and available RBI assessments.
The inspection plan must be created using the most relevant information sources outlined in Section 2 of the inspection code It should be regularly reviewed and updated when new variables affecting damage mechanisms or deterioration rates are discovered, as indicated in inspection reports or Management of Change (MOC) documents For further guidance on developing effective inspection plans, refer to API 572.
5.1.3 Minimum Contents of an Inspection Plan
An effective inspection plan is essential for monitoring damage mechanisms and ensuring the mechanical integrity of equipment such as pressure vessels and pressure-relieving devices It should outline the necessary types of inspections, including internal and external, and specify the next inspection dates for each type Additionally, the plan must detail the inspection and non-destructive examination (NDE) techniques, as well as the extent and locations for these inspections Surface cleaning requirements prior to inspections should also be included, along with any necessary pressure testing details, such as the type of test, test pressure, and duration Finally, the plan should document any previously planned repairs to maintain comprehensive oversight.
Generic inspection plans aligned with industry standards can be utilized, and while these plans may not always be consolidated into a single document, their contents should be easily accessible through inspection data systems.
5.1.4 Additional Contents of an Inspection Plan
Inspection plans should include essential details to clarify their purpose and facilitate execution Key elements may encompass a description of the anticipated or existing types of damage to the equipment, the specific locations of such damage, and any special access requirements necessary for the inspection process.
Risk-Based Inspection (RBI)
RBI (Risk-Based Inspection) is essential for determining inspection intervals and the scope of future examinations by assessing the risk of equipment failure through the combination of probability and consequence A comprehensive RBI assessment, in line with API 580, involves a systematic evaluation of both failure probability and consequences API 581 outlines a methodology that incorporates key elements from API 580, focusing on identifying potential damage mechanisms, current equipment conditions, and the effectiveness of past inspections to evaluate the likelihood of pressure vessel failure Additionally, assessing the consequences involves examining process fluids, potential injuries, environmental impacts, equipment damage, and downtime Identifying Integrity Operating Windows (IOWs) for critical process variables further enhances the RBI approach and aids in planning and scheduling inspections.
The probability assessment for vessel damage must consider all potential damage mechanisms, including corrosion, cracking, and other metallurgical or mechanical issues It is essential to evaluate the effectiveness of inspection practices and tools in identifying these damage mechanisms Key factors in this assessment include the suitability of construction materials, vessel design relative to operating conditions, adherence to design codes and standards, the effectiveness of corrosion monitoring programs, the quality of maintenance and inspection QA/QC programs, compliance with pressure retaining and structural requirements, and both historical and projected operating conditions.
Equipment failure data will also be important information for this assessment.
The impact of a fluid release is influenced by the type and quantity of the process fluid involved A thorough consequence assessment must evaluate potential incidents stemming from the release, including the size and nature of the release, which may involve explosions, fires, or toxic exposures Additionally, the assessment should identify possible outcomes such as health effects, environmental harm, equipment damage, and operational downtime.
Thorough documentation of all RBI assessments is crucial, as outlined in API 580, Section 17, to clearly define the factors influencing the probability and consequences of vessel failure The outcomes of an RBI assessment inform the vessel inspection plan, guiding the selection of appropriate inspection and NDE methods, determining the extent of NDE required, establishing intervals for internal, external, and on-stream inspections, assessing the necessity for pressure testing post-damage or repairs, and identifying prevention and mitigation strategies to minimize the risk and impact of vessel failures.
RBI assessments must be updated after each vessel inspection, as outlined in API 580, Section 15 Additionally, these assessments should be revised whenever there are process or hardware changes that could impact damage rates or mechanisms, as well as following any unexpected failures related to damage mechanisms.
Preparation for Inspection
Safety precautions are crucial during pressure vessel inspection and maintenance due to the potential hazards posed by harmful process fluids and the risks associated with confined space entry Compliance with applicable regulations, such as those enforced by OSHA, is essential for safe vessel entry Additionally, it is important to review and adhere to the owner/user's safety procedures For further guidance on inspection safety, refer to API 572, Section 8.
Before commencing vessel work, it is essential to inspect all tools, equipment, and personal protective gear, including those used for inspection, non-destructive testing (NDE), pressure testing, repairs, and alterations NDE equipment must comply with the safety standards set by the owner or user regarding electrical equipment Additionally, any supplementary equipment, such as planking, scaffolding, and portable ladders, should also be thoroughly checked prior to use Personal protective equipment must be worn as mandated by regulations, the owner, or the repair organization For further details on inspection tools, refer to API 572, Section 8.
Before conducting any inspection or maintenance on a pressure vessel, it is essential to secure permission from the operating personnel in charge When personnel are inside the vessel, it is crucial to notify all individuals working nearby Additionally, those inside the vessel must be informed prior to any work being performed on either the interior or exterior while they are present.
Before entering a vessel, it is essential to isolate it from all sources of liquids, gases, vapors, radiation, and electricity The vessel must be drained, purged, cleaned, ventilated, and gas tested to ensure safety Clear procedures for continuous ventilation and emergency evacuation must be understood by all personnel Documentation of these safety measures is mandatory prior to entry, and permission from responsible operating personnel must be obtained Appropriate personal protective equipment should be worn to safeguard against specific hazards Compliance with all safe entry procedures and regulations is required, and inspectors must ensure that all safety protocols and permits for confined space entry are adhered to before entering the vessel Additionally, inspectors should verify that any connections that could pose hazards have been properly disconnected or blinded.
Before conducting API 510 inspections, inspectors must review the vessel's history, including previous inspection results, repairs, and the current inspection plan They should also consider engineering evaluations and similar service inspections For a comprehensive understanding of damage types and failure modes in pressure equipment, refer to API 571 and API 579-1/ASME FFS-1, Annex G.
Inspection for Different Types of Damage Mechanisms and Failure Modes
Pressure vessels are vulnerable to different types of damage caused by various mechanisms It is essential for inspection plans to include techniques tailored to each potential damage mechanism specific to pressure vessels API 571 outlines common damage mechanisms and the corresponding inspection techniques for their identification Notable examples of these mechanisms include general and localized metal loss.
1) sulfidation and high-temperature H 2 S/H 2 corrosion—refer to API 571, Sections 4.4.2 and 5.1.1.5 and API 939-C;
2) oxidation—refer to API 571, Section 4.4.1;
3) microbiologically induced corrosion—refer to API 571, Section 4.3.8;
4) naphthenic acid corrosion—refer to API 571, Section 5.1.1.7;
5) erosion/erosion-corrosion—refer to API 571, Section 4.2.14;
6) galvanic corrosion—refer to API 571, Section 4.3.1;
7) atmospheric corrosion—refer to API 571, Section 4.3.2;
8) corrosion under insulation (CUI)—refer to API 571, Section 4.3.3;
9) cooling water corrosion—refer to API 571, Section 4.3.4;
10) boiler water condensate corrosion—refer to API 571, Section 4.3.5;
11) soil corrosion—refer to API 571, Section 4.3.9;
12) ammonium bisulfide and chloride corrosion—refer to API 571, Sections 5.1.1.2 and 5.1.1.3;
13) carbon dioxide corrosion—refer to API 571, Section 4.3.6. b) Surface connected cracking:
1) mechanical fatigue cracking—refer to API 571, Section 4.2.16;
2) thermal fatigue cracking—refer to API 571, Section 4.2.9;
3) caustic stress corrosion cracking—refer to API 571, Section 4.5.3;
4) polythionic stress corrosion cracking—refer to API 571, Section 5.1.2.1;
5) sulfide stress corrosion cracking—refer to API 571, Section 5.1.2.3;
6) chloride stress corrosion cracking—refer to API 571, Section 4.5.1. c) Subsurface cracking:
1) hydrogen induced cracking—refer to API 571, Section 4.4.2;
2) wet hydrogen sulfide cracking—refer to API 571, Section 5.1.2.3. d) High-temperature microfissuring/microvoid formation and eventual macrocracking:
1) high-temperature hydrogen attack—refer to API 941, Section 6;
2) creep/stress rupture—refer to API 571, Section 4.2.8. e) Metallurgical changes:
1) graphitization—refer to API 571, Section 4.2.1;
2) temper embrittlement—refer to API 571, Section 4.2.3;
3) hydrogen embrittlement—refer to API 571, Section 4.5.6. f) Blistering:
1) hydrogen blistering—refer to API 571, Section 5.1.2.3.
The likelihood of damage in a vessel is influenced by its construction material, design, and operating conditions Inspectors must understand these factors, as well as the causes and characteristics of potential defects and damage mechanisms.
API 571 provides comprehensive details on corrosion, cracking, and other damage mechanisms, highlighting critical factors, visual indicators, and standard inspection and monitoring techniques For further guidance, API 572 outlines additional recommended inspection practices tailored to various damage mechanisms.
Vessels in cyclic service, which experience varying pressure and temperature, must be assessed for potential fatigue cracking and have suitable inspections scheduled Key considerations include evaluating the fatigue design criteria from the original construction code, along with any specific fabrication details such as ground flush welds and volumetric weld examinations Additionally, the types of internal and external attachments, along with any modifications or damage, should be analyzed for stress intensification that could lead to fatigue cracking The risk of internal or external corrosion, including corrosion under insulation (CUI) and environmental stress corrosion cracking, must also be considered for its impact on the vessel's fatigue life Finally, appropriate non-destructive testing (NDE) methods and inspection frequencies should be established to effectively detect fatigue cracking, including techniques like ultrasonic flaw detection and measurements for weld seam integrity Common examples of vessels in cyclic service include coke drums, mole sieves, and pressure swing adsorbers.
Types of Inspection and Surveillance for Pressure Vessels
5.5.1 Types of Inspection and Surveillance
The appropriate type of inspection, examination, or surveillance for pressure vessels varies based on specific circumstances Key methods include internal inspection, on-stream inspection, external inspection, thickness inspection, CUI inspection, and operator surveillance.
Inspections must follow the designated inspection plan for each vessel, as detailed in Section 6, which outlines the frequency and extent of these inspections Any corrosion or damage found during these evaluations should be characterized, sized, and assessed according to Section 7, with any deviations from the plan requiring approval from the inspector or pressure vessel engineer.
Internal inspections must be carried out by a qualified inspector following the established inspection plan, with assistance from other qualified personnel, such as NDE examiners, only under the inspector's direction These inspections involve a comprehensive examination of the internal pressure boundary surfaces for any damage In cases where the vessel is too small for safe entry or when all internal surfaces are visible and can be adequately assessed from a manway or inspection port, these alternative inspections may be permitted Additionally, remote visual inspection techniques can enhance the evaluation of internal surfaces.
The primary objective of internal inspections is to detect damage that regular external monitoring of CMLs during on-stream inspections may miss Owners or users may require specific non-destructive examination (NDE) techniques, such as wet fluorescent magnetic particle testing, alternating current field measurement, and eddy current examination, to identify damage unique to the vessel or its service conditions, which should be detailed in the inspection plan For comprehensive guidelines on pressure vessel internal inspections, refer to API 572, Section 9.4, and for additional information on the internal inspection of columns and towers, consult API 572, Annex B.
Vessels with removable internals may require partial removal for inspecting pressure boundary surfaces Complete removal is not necessary if there is reasonable assurance that damage in inaccessible areas is not exceeding that found in more accessible regions of the vessel.
The inspector, in collaboration with a corrosion specialist, must assess the need for removing deposits or linings to conduct thorough inspections It is crucial to evaluate whether operating deposits, like coke, effectively protect the vessel or contribute to surface deterioration Conducting spot examinations in specific areas, where deposits are completely removed, may be necessary to accurately assess the condition of the vessel's surface.
Thorough examination of internal linings, such as refractory, strip linings, plate linings, and coatings, is essential If the linings are intact and there are no signs of underlying damage, removal during internal inspections is unnecessary However, if any damage, bulging, or cracking is observed, it may be prudent to remove sections of the linings to assess the condition of both the lining and the vessel surface underneath Additionally, external non-destructive examination (NDE) techniques can be beneficial for detecting damage beneath the linings For detailed guidelines on inspecting pressure vessel linings, refer to API 572, Section 4.3 and Sections 9.4.7 to 9.4.9.
5.5.3 On-stream Inspection of Pressure Vessels
On-stream inspections, as outlined in the inspection plan, must be conducted by a qualified inspector or examiner Any inspection work carried out by an examiner requires prior authorization and approval from the inspector When inspecting the pressure boundary, it is essential to specify the appropriate non-destructive examination (NDE) techniques to effectively identify the damage mechanisms and flaw types detailed in the inspection plan.
The inspection process may involve various examination techniques to evaluate damage mechanisms related to service conditions On-stream inspection techniques are selected for their effectiveness in identifying specific damage mechanisms from the exterior while operating under the pressure vessel's on-stream conditions, such as metal temperatures Typically, thickness examination, as outlined in section 5.5.5, is included in the on-stream inspection.
When utilizing external non-destructive testing (NDE) techniques to identify internal damage, several inherent limitations must be considered These limitations can be influenced by factors such as the construction material (alloy), the type of parent material (plate, pipe, or casting), the presence of weldments, nozzles, support saddles, and reinforcing plates, as well as internal attachments and linings or claddings Additionally, physical access, equipment temperature, and the specific limitations of the chosen NDE technique to detect the damage mechanism play crucial roles in the effectiveness of the inspection process.
On-stream inspection can be permitted instead of internal inspection for vessels under certain conditions outlined in section 6.5.2 When on-stream inspection is deemed acceptable, it can be performed whether the vessel is under pressure or depressurized.
5.5.4 External Inspection of Pressure Vessels
Visual external inspections are typically carried out by an inspector, but other qualified personnel may also perform these inspections if approved by the inspector Those conducting the external inspection must be trained and qualified as outlined by the owner or user, in accordance with API 510 standards.
External inspections are crucial for assessing the condition of a vessel's exterior, including its insulation, painting, coating systems, supports, and overall structure These inspections focus on identifying issues such as leakage, hot spots, vibration, and alignment on supports Special attention should be given to welds connecting components, as they may exhibit cracks or defects Investigating any signs of leakage is essential to determine their sources, and weep holes in reinforcing plates should remain unobstructed to allow for visual detection of leaks and to prevent pressure buildup.
Vessels must be visually inspected for signs of bulging, out-of-roundness, sagging, and distortion If any distortion is suspected or detected, the vessel's overall dimensions should be measured to assess the extent of the issue For detailed guidance on the external inspection of pressure vessels, refer to API 572, Section 9.3 It is essential for personnel to report any observed deterioration of the vessel to the inspector.
Buried vessels must be inspected to assess their external surface condition, with the inspection frequency determined by evaluating the effectiveness of the cathodic protection system and corrosion rate data This data can be obtained through various methods, including maintenance activities on connecting piping of similar materials, periodic examinations of buried corrosion test coupons, assessments of representative sections of the actual vessel, or evaluations of vessels in comparable conditions.