Pressure vessels Repairs and Alterations
In the Oil, Gas and Chemical industries vessels may remain in use for 30 years or more. Process designs become more efficient. The equipment which feeds or is fed by this vessel becomes a bottleneck in the production throughput as time passes. Capital expenditures for new equipment may not be in the current budge. Here comes the requirement of Vessel repair or a nozzle replacement or to use some updated to make them more efficient.
This blog will discuss Repairs and Alterations to ASME Code Stamped Pressure Vessels. This topic is covered by API 510, ASME Section VIII and the National Board Inspection Code (NBIC).
During the service life of an ASME Code Stamped Pressure Vessel, instances can arise when repairs are needed. Repairs on ASME Code Stamped Pressure Vessels are covered by a different code than the manufacture of the ASME Code Stamped Pressure Vessel. When an ASME Code Stamped Pressure Vessel is built, it is built following the ASME Boiler and Pressure Vessel Code. Repairs, however, are covered by the National Board Inspection Code, commonly referred to as the NBIC.
The NBIC consists of three parts; Part 1 Installation, Part 2 Inspection, and Part 3 Repairs and Alterations. In this blog, we will be focusing on Part 3 Repairs and Alterations. The first step in the repair of the ASME Code Stamped Pressure Vessel is determining if the repair falls under the requirements of the NBIC. Things such as changing a low water cutoff or a pressure switch would not fall under the NBIC. Section 3.3.3 of the NBIC provides examples of repairs that do fall under the NBIC. These repairs include, but are not limited to; weld repairs, weld buildup of corroded areas, installation or replacement of nozzles, attachment of parts such as studs for insulation, and mounting clips for ladders to pressure parts. It’s important to note that attachment of non-pressure bearing parts to pressure boundary components constitutes a repair.
The second major step in the repair of ASME Code Stamped Pressure Vessel is to locate a shop which can perform the work to the requirements of the NBIC. The shop must have a Certificate of Authorization to use the “R” symbol, as opposed to the Certificate of Authorization to apply the “NB” mark used when the pressure vessel was fabricated.
While these two codes may seem similar, there are key differences, including testing and documentation. During fabrication, pressure vessels are commonly tested at a pressure 1.3 times the pressure rating, however, the NBIC specifies the pressure shall be the minimum required to verify the integrity of the repair, but without exceeding 150% of the maximum working pressure of the vessel. Subtle differences in documentation also exist. When the ASME Pressure Vessel is built, a U1 or U1A form is submitted to the National Board of Boiler and Pressure Vessel Inspectors. For a repair, the NBIC does not require submittal of the R1 form to the Board. A third subtle difference is in the requirements of the repair nameplate. While the original name plate attached to the vessel lists the year of manufacture, the repair name plate must include the full date of the repair, including the month, day and year.
Following are several noteworthy requirements in Part 3 of the NBIC:
1. General Requirements (2013 NBIC §1.2(a))
When the standard governing the original construction is the ASME Code or ASME RTP-1, repairs and alterations to pressure-retaining items shall conform, insofar as possible, to the section and edition of the ASME Code most applicable to the work planned.
2. Inspector/Authorization/Acceptance Inspection
Per 2013 NBIC §1.3, all repairs and alterations must be inspected and authorized by an Authorized Inspection Agency. The company performing the modification is required to receive National Board Accreditation (procedure for accreditation is outlined in 2013 NBIC §1.5) in order to use the “R” stamp. Part of the accreditation process is the development of a Quality System (2013 NBIC §1.6) which the company must have available for review upon request. The Quality System Manual should indicate which construction code requirements are being followed for the repair/alteration.
3. Material Requirements for Repairs and Alterations (2013 NBIC §3.2.1)
a) The materials used in making repairs or alterations shall conform insofar as possible to the original code of construction or construction standard or code selected, including the material specification requirements used for the work planned…
c) When ASME is the original code of construction, replacement parts subject to internal or external pressure fabricated by welding, which require inspection by an Authorized Inspector shall be fabricated by an organization having an appropriate ASME Certificate of Authorization. The item shall be inspected and stamped as required by the applicable section
of the ASME Code. A completed ASME Manufacturer’s Partial Data Report shall be supplied by the manufacturer;
To summarize the excerpts above, it is expected that the repair/alteration would conform to the ASME B&PV Code and that the company performing the vessel modification would provide a partial/revised data report upon completion.
4. Drawings (2013 NBIC §3.2.3)
As appropriate, drawings shall be prepared to describe the repair or alteration. Drawings shall include sufficient information to satisfactorily perform the repair or alteration.
5. Design Requirements for Repairs and Alterations (2013 NBIC §3.2.4(b))
The “R” Certificate Holder performing repairs and alterations shall establish the construction standard or code and sufficient controls to ensure that all required design information, applicable drawings, design calculations, specifications, and instructions are prepared, obtained, controlled, and interpreted to provide the basis for a repair or an alteration in accordance with the original code of construction. When a Manufacturer’s Data Report is required by the original construction standard, a copy of the original data report shall be obtained, where available, for use in the design of the repair or alteration. When the original Manufacturer’s Data Report cannot be obtained, agreements on the method of establishing design basis for the repair or alteration shall be obtained from the Inspector and the Jurisdiction, when required.
6. Calculations (2013 NBIC §3.2.5)
For alterations, calculations shall be completed prior to the start of any physical work. All design calculations shall be completed by an organization experienced in the design portion of the standard used for construction of the item. All calculations shall be made available for review by the Inspector accepting the design.
7. Repair vs. Alteration
The NBIC lists several examples of both repairs (§3.3) and alterations (§3.4).
Examples of repairs are:
· replacement/repair of welds that have failed
· addition of welded attachments
· replacement of tube sheets or tubes in a heat exchanger
· installation of new nozzles that do not effect the original vessel strength calculations
Examples of alterations are:
· re-rating a vessel for a higher temperature or pressure
· re-rating a vessel based on new code edition and new material strength and wall thickness requirements
· addition of new nozzles and openings that are not classified as a repair (see above)
· change in dimensions of a vessel
With this in mind, it is important to determine whether the vessel is being repaired or altered as the requirements differ for each category. In either case, requirements for the repair/alteration a spelled out in NBIC.
8. Examination and Testing
2013 NBIC §4 outlines the requirements for Examination and Testing after performing a repair or alteration. It is beyond the scope of this blog to go into great detail about the various methods of examination, but important to note the following:
For a repair, exclusive use of Visual Examination is permitted if other methods are not practicable and the repair is classified as “routine” (definition of routine is in §3.3.2). The person performing the visual inspection must be qualified and certified in accordance with AWS QC-1. The visual examination must be accompanied by a written procedure and a report of the examination results. Exclusive use of Visual Examination is not allowed for alterations.
9. Certification/Documentation and Stamping
Per 2013 NBIC §5.2 either an R-1 (repair) or R-2 (alteration) form must be prepared and available at the facility and submitted to the National Board.
2013 NBIC §5.7.5 outlines the various requirements for nameplates/stamping. It is worth noting that the nameplate/stamp requirements differ for an alteration as compared to a repair.
**The content of this article is taken from web open source. The blogs are intended only to give technical knowledge to young engineers. Any engineering calculators, technical equations, and write-ups are only for reference and educational purposes.