{"slug":"/standards/nbic-nb-23","title":"NBIC NB-23: Repairs and Alterations to Pressure Equipment","description":"NBIC NB-23 Part 3 governs in-service repair and alteration: R Certificate of Authorization, Form R-1 or R-2, and an alteration test at 1.3 x MAWP.","h1":"NB-23 in Practice: Where a Repair Ends and an Alteration Begins","answer":"NBIC NB-23 is the National Board Inspection Code, the rulebook for pressure-retaining items after they leave the manufacturer. Part 3 governs repairs and alterations: work must be done by an organization holding a National Board R Certificate of Authorization, accepted by a commissioned Inspector, and documented on Form R-1 for a repair or Form R-2 for an alteration.","expansion":"The code is published by the National Board of Boiler and Pressure Vessel Inspectors on a two-year cycle and is split into three parts: Part 1 covers installation, Part 2 covers in-service inspection, and Part 3 covers repairs and alterations. Part 3 is the part most people mean when they say NB-23. It has no authority of its own. NBIC becomes law only where a jurisdiction adopts it, and the jurisdiction, not the code, decides whether a given vessel falls under NBIC or under an owner-user inspection programme run to API 510, API 570 or API 653. Part 3 also does not govern new construction. The moment a pressure-retaining item is stamped and its Manufacturer's Data Report is signed, ASME construction rules stop and NBIC picks up. Everything after that point, including replacement in kind, re-rating, weld build-up and nozzle addition, is judged against the repair-or-alteration distinction in Part 3.","source":"National Board Inspection Code NB-23, Part 3, Repairs and Alterations (National Board of Boiler and Pressure Vessel Inspectors); ASME BPVC Section VIII Division 1; ASME BPVC Section IX; API 510 Pressure Vessel Inspection Code; API 579-1/ASME FFS-1 Fitness-For-Service","table":{"caption":"Repair or alteration under NB-23 Part 3, and where the classification goes wrong","columns":["Work performed","Classification","Form","Consequence of the classification","Where crews get it wrong"],"rows":[["Weld build-up to restore lost wall thickness within the original design","Repair","R-1","R symbol stamping, Inspector acceptance, NDE per original code of construction","Treating it as routine maintenance and producing no form at all"],["Replacing a nozzle with an identical size, material specification and rating","Repair","R-1","No design review against the Manufacturer's Data Report required","Substituting a different material specification and still writing an R-1"],["Adding a nozzle larger than the size the original design covered","Alteration","R-2","Design calculations, alteration nameplate, registration where the item was registered","Calling it a repair because the nozzle is physically small"],["Increasing the maximum allowable working pressure","Alteration (re-rating)","R-2","Pressure test per the original code of construction, new nameplate showing the new rating","Documenting a re-rating by calculation alone with no form and no nameplate"],["Lowering the design temperature below the original range","Alteration (re-rating)","R-2","Identical route to an upward re-rating","Assuming a derating is not a re-rating because nothing got more onerous"],["Replacing a shell course with a different plate grade","Alteration","R-2","Without the R-2 the Data Report no longer describes the item that exists","Calling it replacement in kind because the substitute grade is stronger"],["Fabricating a replacement pressure part off site for later installation","Fabricated part","R-3","The part travels with its own form, referenced by the installing organisation","Installing the part with no form and no traceability to the heat"],["Repair of a pressure relief valve","Valve repair","VR programme","Requires a National Board VR Certificate of Authorization, not the R Certificate","Assuming R authorisation extends to relief valve repair"]],"note":"Classification decides the form, the signatory, whether design calculations are needed, whether a nameplate changes and whether the completed form is registered with the National Board. Where the classification is genuinely arguable, agree it with the Inspector in writing before the work starts, not at form-signing."},"facets":[{"q":"Is replacing a nozzle with an identical nozzle a repair or an alteration?","a":"Identical replacement, same size, same material specification and same rating, is a repair and goes on Form R-1. It becomes an alteration the moment any of those change: a nozzle larger than the size the original design covered, a different material specification, a lower allowable stress, or a change to the reinforcement arrangement. The test is whether the original Manufacturer's Data Report still describes the item accurately once the work is finished."},{"q":"Does an ASME U stamp allow a shop to perform an NB-23 repair?","a":"No. An ASME Certificate of Authorization covers new construction up to the point the Manufacturer's Data Report is signed. Repairs and alterations to items already in service require a National Board R Certificate of Authorization, with a quality system manual audited for that scope and for the alternative welding methods, NDE methods and forms the organisation intends to use. Holding both is common, but one does not substitute for the other."},{"q":"What pressure test is required after an alteration?","a":"A test in accordance with the original code of construction, not the current one. A vessel built to a current edition of ASME Section VIII Division 1 is tested at 1.3 times MAWP corrected by the ratio of allowable stress at test temperature to allowable stress at design temperature; a vessel built to a pre-1999 edition uses 1.5. Where a test is impractical, Part 3 permits substitute nondestructive examination with the Inspector's acceptance, documented on the form."},{"q":"Can a repair weld be made without post-weld heat treatment?","a":"Yes, through the alternative welding methods in Part 3, of which controlled deposition and temper bead techniques are the most used. They rely on the tempering effect of subsequent beads to condition the heat-affected zone below. The conditions are strict: a procedure qualified specifically for the method, controlled preheat and interpass temperature, defined bead placement and sequence, the required post-weld hold, and hardness or toughness verification wherever the original code demanded toughness."},{"q":"Who signs Form R-1 and where does it go?","a":"The repair organisation's authorised representative signs it, and an Inspector holding a valid National Board commission signs the acceptance. A copy goes to the owner, a copy to the jurisdiction where required, and where the item was originally registered with the National Board the completed form is registered as well. A lapsed commission number on the Inspector line invalidates the form regardless of how good the weld was."},{"q":"Does NB-23 apply if the plant already runs an API 510 programme?","a":"It depends on the jurisdiction. Where the jurisdiction has accepted the owner-user inspection programme, API 510 can govern repairs, alterations and re-ratings of those vessels and no R stamp is required. Where it has not, or for jurisdictional boilers, NB-23 applies and the repairing organisation needs an R Certificate. Many sites run both regimes across different assets, which is exactly why purchase orders should name the governing code explicitly."}],"sections":[{"heading":"What Part 3 covers, and the line where ASME stops","paragraphs":["NB-23 is issued by the National Board of Boiler and Pressure Vessel Inspectors and is organised in three parts. Part 1 covers installation. Part 2 covers in-service inspection, including boilers, pressure vessels, piping and pressure relief devices. Part 3 covers repairs and alterations, and it is the part almost every search for NB-23 is actually about. Part 3 reaches welding, examination, pressure testing, documentation and stamping for any pressure-retaining item that has already been placed in service.","The boundary with the construction codes is sharp. Until the Manufacturer's Data Report is signed and the item is stamped, ASME Section I, IV or VIII governs and the manufacturer's Certificate of Authorization applies. From that signature onward the construction rules no longer have a mechanism to accept new work, and NB-23 supplies one. This is why an ASME U stamp does not authorise an in-service repair. Repairing a vessel already in service requires a National Board R Certificate of Authorization and a quality system accepted for that scope, which is an entirely separate audit.","Part 3 also does not decide fitness for service. It tells you how to execute and document work, not whether the equipment should be run at all. Remaining life, corrosion rate and the decision to accept a locally thinned area come from Part 2 inspection data and, where the assessment must be quantified, from API 579-1/ASME FFS-1. Keeping those two questions separate matters, because a technically flawless R-1 on a vessel that should have been derated is still a bad outcome. Getting the assessment and the repair route decided together is where [ASNT Level III consulting](/consulting) earns its place."]},{"heading":"Repair or alteration: the distinction that drives everything else","paragraphs":["A repair under Part 3 is work necessary to restore a pressure-retaining item to a safe and satisfactory operating condition, with no change to the item as described on the original Manufacturer's Data Report. An alteration is a change to that description which affects the pressure-retaining capability, or any change in the rated conditions. Get this classification wrong and every downstream artefact is wrong with it: the form, the signatory, the design review, the nameplate and the registration.","The triggers that make work an alteration are more specific than people expect. An increase in maximum allowable working pressure is an alteration. So is a change in design temperature outside the original range, in either direction, because a derating is still a re-rating. So is the addition of a nozzle larger than the size the original design covered, the replacement of a pressure part with a material of different specification or lower allowable stress, and an increase in the heating surface of a boiler. None of these look dramatic on a work order.","The most common misclassification is replacement in kind that is not in kind. A shell course replaced with a different plate grade, even a stronger one, is an alteration, because the Data Report no longer describes the item that exists. Weld metal build-up to restore lost wall is a repair; weld metal build-up used to justify a thinner original design basis is not. When the classification is genuinely arguable, it is settled with the Inspector before the work starts, in writing, rather than discovered when the form is presented for signature."]},{"heading":"Welding, and the route around post-weld heat treatment","paragraphs":["Part 3 requires welding to be performed with procedures qualified to ASME Section IX or to the original code of construction, by welders with current continuity records. That much is routine. What is not routine is post-weld heat treatment. A vessel in a rack, with internals, insulation, attached piping and a corrosion-product loaded surface, frequently cannot be heat treated in the field without creating more risk than the repair removes.","NB-23 answers this with a set of alternative welding methods, of which the controlled deposition and temper bead techniques are the ones most used. They exploit the tempering effect of a subsequent weld bead on the heat-affected zone of the bead below it to produce acceptable hardness and toughness without a formal PWHT cycle. The price is control: a procedure qualification specific to the method, defined preheat and interpass temperature, bead placement and sequence, a controlled post-weld hold where required, and hardness or impact testing wherever the original code demanded toughness.","This is where audits land. The recurring finding is a shop that uses a temper bead technique because NB-23 permits it, while the method is not listed in the organisation's quality system manual, the WPS was qualified for the process but not for the alternative method, and the Inspector never accepted its use. Those are three separate non-conformances on one weld. If your written practice, procedure library and quality manual are not aligned before mobilisation, the weld is not the thing you will end up arguing about."]},{"heading":"Examination and pressure testing after the weld","paragraphs":["Nondestructive examination follows the original code of construction. Where that code is obsolete or the original is unknown, Part 3 permits a current code to be used with the concurrence of the Inspector, which is a practical allowance for equipment older than the records describing it. The examination method is not a free choice; substituting ultrasonic testing for radiography is available only where the referencing code permits it and where the procedure has been demonstrated.","Pressure testing is where remembered numbers do damage. An alteration normally requires a pressure test in accordance with the original code of construction. For a vessel built to ASME Section VIII Division 1 in a current edition that is 1.3 times MAWP corrected by the ratio of allowable stresses at test and design temperature. For a vessel built to a pre-1999 edition the applicable factor is 1.5. Technicians who apply 1.5 to a modern vessel, or 1.3 to an old one, are not applying the code, they are applying a memory, and on a corroded shell the first of those errors is not academic.","Where a pressure test is impractical, Part 3 allows substitute nondestructive examination with the Inspector's acceptance, and that substitution has to be recorded rather than left implied. Whatever is done, the test record needs a calibrated gauge with a range appropriate to the test pressure, hold time, test medium temperature relative to the minimum design metal temperature, and a named witness. An [independent review of the completed inspection reports](/report-validation) before the package leaves site catches most of these while the crew is still standing next to the vessel."]},{"heading":"Forms, stamping and the registration nobody chases","paragraphs":["Part 3 closes with documentation and stamping. A repair is recorded on Form R-1, an alteration on Form R-2, fabricated parts on Form R-3, and continuation data on Form R-4. Each form is signed by the repair organisation's authorised representative and by an Inspector holding a valid National Board commission, and where the item was originally registered with the National Board, the completed form is registered too. Copies go to the owner and, where required, to the jurisdiction.","Stamping follows the same split. Repairs are marked with the R symbol together with the organisation's name and the date. An alteration that changes the rating carries a nameplate showing the new maximum allowable working pressure and temperature, so the next inspector reads the current rating off the equipment rather than out of a file. If a re-rated vessel still carries only its original nameplate, the re-rating is functionally invisible in the field.","The findings auditors actually write are almost always documentary. A wrong NBIC edition cited. An original code of construction stated as ASME VIII with no division. NDE reports referenced by a number that does not exist in the file. An Inspector commission that lapsed between the field work and the signature date. Forms completed but never registered. Keeping repair records, NDE reports, welder continuity and calibration certificates in one controlled system rather than four folders is the cheapest fix available, and it is exactly what an [inspection management system](/erp) is for."]},{"heading":"Living alongside API 510, API 570 and API 653","paragraphs":["The relationship between NB-23 and the API in-service codes confuses more procurement engineers than any other part of this subject. Both describe repairs, alterations and re-rating of equipment in service, and they do not say identical things. Which one governs is not decided by the plant and not decided by the contractor. It is decided by the jurisdiction.","Where a jurisdiction has accepted an owner-user inspection programme, API 510 for pressure vessels, API 570 for piping or API 653 for storage tanks can govern repairs and alterations, and no R stamp is required. Where it has not, or where the item is a jurisdictional boiler, NB-23 applies and the repair organisation must hold the R Certificate. Some sites live under both regimes at once across different assets. The trap is a purchase order that names the wrong one, because the deliverable set differs completely.","Atlantis operates in this space as the technical authority and the examination provider. We write and qualify procedures, supply Level II and Level III examination, review radiographs and reports, and build the documentation package. We are not the API inspector of record, we do not provide API inspector certification training, and we are not the auditor of your process safety management programme. Where the mechanical integrity side of the file also has to hold together, the equipment records themselves are the evidence, which is why [mechanical integrity software](/mechanical-integrity-software) and the repair record set should be designed as one thing."]},{"heading":"The findings that repeat on NB-23 packages","paragraphs":["Across repair packages the same handful of problems recur, and none of them are exotic metallurgy. Work classified as a repair that met an alteration trigger. Routine repair provisions used for work the jurisdiction never accepted as routine, and used without an R-1 on the theory that routine means undocumented. Alternative welding methods applied without the qualification record that makes them legal in the first place.","Then the examination layer. Radiographic film or digital images never reviewed and signed by a Level III. Technique sheets naming a transducer frequency the calibration block was not scanned with. Personnel certified under a written practice that references an edition of SNT-TC-1A the employer no longer holds a copy of. Hardness surveys taken on the weld cap only, when the hard microstructure sits at the root side of the heat-affected zone.","Finally the paper. Material test reports for the replacement plate absent, or not traceable to the heat number stamped on the part. Pressure gauge calibration expired at the date of test. The R-1 registered late or not at all. Each of these is individually trivial and collectively they are why a repair package is rejected months after the vessel went back into service, when the crew has demobilised and nobody can reconstruct what was done."]},{"heading":"How the inspection team is deployed","paragraphs":["Repairs do not happen on a convenient schedule and they rarely happen where the technical authority sits. Atlantis mobilises inspection teams from Houston and Hyderabad to the client's site or to the repair shop, and once mobilised the team stays deployed for the duration of the contract. For an outage that means the same technicians from the first bore inspection through to the final hydrotest witness.","Continuity is the point. One inspector who has read the vessel's history, who knows which welds were repaired in the last turnaround and what the Inspector accepted last time, will interpret an indication faster and argue it more credibly than a rotating pool ever will. On a campaign spanning several units, that continuity is what keeps the repair-or-alteration decisions consistent from the first R-1 to the last.","Where personnel certification also has to be demonstrable, examination personnel are qualified and certified under a written practice to SNT-TC-1A or ISO 9712, and [NDT training and certification](/training) can be run against your own written practice rather than a generic syllabus. To scope a repair support package, [talk to us about the asset and the jurisdiction](/contact)."]},{"heading":"Jurisdictional variation: why an NB-23 repair accepted in one state can be questioned in another","paragraphs":["NB-23 is a National Board code, but its enforcement runs through the individual state, provincial or municipal jurisdiction where the equipment operates, and jurisdictions retain the authority to impose additional requirements or interpretations on top of the base NB-23 text. A repair procedure accepted without additional scrutiny in one jurisdiction can be questioned or require supplementary approval in another, even though the repair itself is identical and the base code being cited is the same document.","This matters commercially for any organisation operating pressure equipment across multiple states — a repair methodology validated and routinely accepted at one site cannot be assumed to transfer unchanged to a site in a different jurisdiction without confirming that jurisdiction's specific requirements, which are typically published as jurisdictional variations or bulletins rather than embedded in the NB-23 text itself.","The practical control is to confirm jurisdictional requirements before a repair or alteration procedure is finalised for a specific site, not after the work is complete, since a jurisdiction that requires additional review or documentation beyond base NB-23 will not retroactively accept a completed repair on the basis that it complied with the national code alone."]}],"faq":[{"q":"How often is NB-23 revised?","a":"The National Board publishes NB-23 on a two-year cycle, with interpretations issued between editions. The edition that applies to a given repair is normally the edition adopted by the jurisdiction at the time of the work, not the newest one on the shelf. Citing the wrong edition on an R-1 is one of the most common documentary findings, and it is entirely avoidable by confirming the adopted edition before mobilisation."},{"q":"What is a routine repair under NB-23?","a":"Routine repair is a provision allowing certain low-risk, well-defined repairs to proceed without the Inspector performing in-process inspection at every stage. It is not a licence to skip paperwork. The categories of work treated as routine must be defined in the repair organisation's quality system manual and accepted by the jurisdiction and the Inspector, and a Form R-1 is still completed and signed."},{"q":"What is Form R-3 used for?","a":"Form R-3 is the Report of Fabricated Parts, used when an organisation fabricates a replacement pressure part to the original code of construction for installation in an existing item without itself performing the installation. It travels with the part to the repair organisation, which references it on the R-1 or R-2 for the item the part is installed into."},{"q":"Does NB-23 cover pressure relief devices?","a":"Yes. Part 2 addresses their inspection and Part 3 addresses their repair, but repair is performed by organisations holding a National Board VR Certificate of Authorization rather than the R Certificate, with the VR symbol applied to the repaired valve. Vessel repair authorisation does not extend to valve repair; they are separate certificates with separate quality system requirements."},{"q":"Can nondestructive examination replace the pressure test after a repair?","a":"Part 3 allows substitute examination where a pressure test is impractical, subject to acceptance by the Inspector. The substitution has to be justified, the examination has to be capable of finding the flaw types the test would have revealed, and both the justification and the method must appear on the form. Treating it as a default rather than an exception is what draws findings."}]}