Ask The Engineer
Alex Garbolevsky
Senior Engineer, HSB Codes & Standards
Pressure Points Newsletter - June 2025
properties.trackTitle
properties.trackSubtitle
Question
Does paragraph 3.4.2 (Alterations Based on Allowable Stress Values) of the National Board Inspection Code (NBIC) Part 3 apply exclusively to re-rating a pressure-retaining item or calculating new minimum wall thickness? Or can it also be applied to other types of alterations or replacement components, particularly when a manufacturer uses materials designed to the latest edition of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (Code)?
Answer
It depends. Consider a pressure vessel built in the 1950s that now requires the addition of a 6-inch diameter nozzle. When performing reinforcement calculations — specifically, determining the required area and the available area in the shell — must the original Code of construction’s stress values be used for all components? Or can the certificate holder apply the higher allowable stress values from the most current edition of the Code for the new nozzle and its reinforcement?
Historically, NBIC Part 3 paragraph 3.4.2 has been predominantly used for re-rating pressure-retaining items by applying increased allowable stress values to existing materials. However, the title and language of this NBIC paragraph do not explicitly restrict its application to re-rates and do not exclude other types of alterations.
General consensus on the application of paragraph 3.4.2 is as follows:
1. For pressure-retaining items constructed to the 1968 Edition/Addenda of the Code or later:
- Higher allowable stress values may be applied to both existing and new materials, provided that all other conditions specified in paragraph 3.4.2 are satisfied.
2. For pressure-retaining items constructed prior to the 1968 Edition/Addenda:
- Replacement components (such as nozzles) may be designed in accordance with either the original Code of construction or the latest edition of the Code. This same principle also applies to repairs.
- In reinforcement area calculations:
- New materials may be designed using the higher allowable stress values from the latest Code edition.
- However, when evaluating the existing shell material, the original stress values from the applicable Code of construction must be used to determine the shell’s contribution to the reinforcement area.
About the author
Alex Garbolevsky, P.E. | Senior Engineer | alex_garbolevsky@hsb.com
Alex joined HSB in 1979, after serving in the U.S. Navy as a Main Propulsion Assistant. He holds a B.A. in Chemistry from the College of the Holy Cross and an M.S. in Engineering Science from Rensselaer Polytechnic Institute. Prior to his assignment to Codes & Standards in 2000, he spent 13 years in Germany and represented HSB in more than 25 countries, serving in positions ranging from Authorized Inspector to Technical Managing Director of our subsidiary, HSB International GmbH.
Alex concentrates on providing support for ASME Section V and IX, as well as for the European Union Pressure Equipment Directive “PED” (2014/68/EU) and ASME Section III. He is actively involved in inspector training within the company, as well as presenting external ASME and National Board Code-related seminars. Alex holds National Board “AI” and “IS” Commissions with “B,” “I,” “N,” “NS,” and “R” endorsements. From 1993 to 2002, he served as Chairman of ISO/TC-11 Technical Committee for Boilers and Pressure Vessels and is currently a member of ASME’s Standards Committee on Nondestructive Examination, Subgroup on International Materials Specifications, Subgroup on Volumetric Methods, Working Group Radiography, Subgroup on Surface Examination Methods, and Subgroup on Brazing. He is a Registered Professional Engineer (Mechanical) in the Commonwealth of Massachusetts.
