Non-destructive testing — Building code requirements and IAS AC472 accreditation
To help determine non-destructive testing requirements of the applicable building code and to establish minimum practices and procedures for maintaining AC472 accreditation, the International Accreditation Service (IAS) and the Metal Building Manufacturers Association (MBMA) provide the following information and answers to frequently asked questions. Readers are encouraged to review reference sections cited in the codes/standards to verify that the summary provided herein is applicable to a specific situation.
The applicable building code edition referenced in the contract documents determines the required edition of the referenced material design specifications, [American Institute of Steel Construction (AISC) 360, AISC 341 etc.]. For the purposes of this paper, discussion focuses on the requirements in the most recent and widely adopted model building code – the 2018 International Building Code (IBC), and therefore AISC 360-16 and AISC 341-16.
The best way to control weld quality is by controlling the process, not by performing NDT after the fact. Even so, inspections related to quality control (QC) are routinely carried out by the metal building manufacturer that include visual examinations of welds and may also include nondestructive testing (NDT) of welds. Inspections related to quality assurance (QA) are traditionally carried out by others (third party inspection) and these QA inspections are referred to as “special inspections” in the building code. However, as discussed below, a metal building manufacturer may not only be exempt from specific special inspections required by the IBC, but also may be able to carry out special inspections and NDT using their own certified personnel.
Special inspections for fabricated structural steel construction are covered in IBC Section 1705.2. This section requires special inspections and NDT to be in accordance with AISC 360. A higher level of special inspection and NDT in accordance with AISC 341 is required for steel used in seismic force-resisting systems as specified in IBC Sections 1705.12 and 1705.13, respectively.
The AISC 360 requirements for NDT inspections were introduced in the 2010 edition, which was subsequently adopted by reference in the 2012 IBC. Therefore, the specific edition of the applicable building code referenced for a job will impact the minimum inspection requirements.
The role of IAS
MBMA has collaborated with IAS, a wholly owned subsidiary of the International Code Council, to develop the IAS Inspection Program for Manufacturers of Metal Building Systems (AC472). “IAS was pleased to work with MBMA on creating, and now maintaining, this accreditation program,” said Sandi McCracken, director of construction and industrial relations for IAS. “A proactive association, MBMA members demonstrate commitment to quality and code compliance through active accreditation committee meetings and the IAS accreditation process.” This comprehensive, third-party accreditation program is based on the requirements of Chapter 17 of the IBC and provides building owners, specifiers and code officials with a means to approve the QC inspection programs of manufacturers that fabricate metal buildings. “MBMA and IAS have worked closely to ensure that the AC472 program elevates the quality of metal buildings, and understanding the role of the code and standards requirements for special inspections is essential” said Dr. Lee Shoemaker, director of research and engineering at MBMA.
If the fabricator has been recognized as an “Approved Fabricator” by the building official, then according to IBC Section 1704.2.5.1, the fabricator is exempt from special inspections. The exemption is based on the recognition that a properly designed and executed QC plan will satisfy the goals of a special inspection program. Building officials can utilize IAS AC472 accreditation to help identify and recognize metal building manufacturers that qualify as approved fabricators. “IAS is pleased to have added section item 188.8.131.52 “Nondestructive Testing” to the AC472 program which allows the recognition of performing In-House UT weld Inspections following the indicated requirements, having a documented procedure, maintaining documented evidence, and having the necessary personnel on staff to perform properly. When an organization meets these requirements, special recognition is added to their Certificate,” said Walter Mershon, associate director of programs for IAS. A metal building manufacturer who is recognized as an approved fabricator by the building official would be exempt from special inspections, but they are required to provide a certificate of compliance to the owner or owner’s authorized agent to be submitted to the building official stating that the work has been performed in accordance with the approved construction documents. “I’m proud to be part of an industry and a trade association that takes accreditation so seriously that we made it a requirement of membership,” said Tony Bouquot, general manager at MBMA.
Specification for Structural Steel Buildings (AISC 360) – Chapter N, Quality Control and Quality Assurance, addresses minimum requirements for quality control, quality assurance, and nondestructive testing for structural steel systems for buildings.
Seismic Provisions for Structural Steel Buildings (AISC 341) – Chapter J, Quality Control and Quality Assurance, addresses requirements for quality control and quality assurance for structural steel members and connections in the seismic force-resisting systems.
What follows are frequently asked questions about AC472 and its relationship with the IBC, AISC 360 and AISC 341.
Are special inspections required during fabrication for an AC472 accredited metal building manufacturer?
Not typically. Code requirements related to special inspections are specified in the IBC. The IBC permits building officials to designate approved fabricators, who are then exempt from special inspections in accordance with IBC Section 1702.5.1. Building officials can utilize AC472 accreditation for approval of metal building manufacturers who would then be exempt from special inspections.
Keep in mind that the approved construction documents may have additional inspection requirements above and beyond the IBC that would not be covered by the same exemption.
When an approved metal building manufacturer is exempt from IBC special inspections, are the NDT requirements in AISC 360 Chapter N and AISC 341 Chapter J also waived?
This really depends on the approved construction documents for the project. AISC 360 clearly states that NDT requirements must be carried out, even when the QA or special inspections are waived for an approved fabricator. However, AISC 360 permits the approved fabricator to perform their own NDT with approval of the building official. This is different from the IBC exemption for special inspections, which does not specifically include a waiver of third-party NDT. Therefore, if the approved construction documents clearly state that the project is governed by AISC 360 and AISC 341 (or by reference in IBC), then NDT would not be automatically waived, but could be performed by the metal building manufacturer if approved by the building official (see FAQ below). In any case, all records of inspection and testing must be on file and submitted to the EOR and the building official upon request.
Are AC472 accredited metal building manufacturers allowed to perform NDT with their own personnel?
Yes. Special inspections regarding NDT required by Chapter 17 of the IBC are permitted to be performed by an approved fabricator using their own properly qualified personnel. However, the approved fabricator must have a fully qualifying NDT program which includes Written Practices and Written Procedures Approved by an ASNT Central Certification Program (ACCP) Professional Level III qualified in the NDT method used by the metal building manufacturer. When the approved fabricator performs the NDT, the QA agency must review the fabricator’s NDT reports and verify that the Level III (or Level II designated by the Level III), has signed off on the NDT documentation.
Note that IAS AC472 added an optional endorsement in 2019 that provides an audit of a metal building manufacturer’s in-house capabilities for nondestructive testing of structural steel elements (following the requirements of performing ultrasonic testing) in accordance with Chapter N of AISC 360.
When metal building manufacturers perform NDT in lieu of a third-party, what are the requirements to have personnel certified?
Where inspections are required of the seismic force-resisting system in accordance with AISC 341, additional qualification in accordance with AWS D1.8 Structural Welding Code – Seismic Supplement, clause 7.2.4 is required. The only substantial differences are that the inspections must be completed by an NDT Level II or Level III and the inspector must comply with AWS D1.8 Annex F, which contains supplementary ultrasonic technician qualifications.
MBMA has developed a template for a metal building manufacturer to use in developing and implementing a written practice that meets these requirements, based on the specific welding inspection needs. A metal building manufacturer who is an approved fabricator and plans to use their own certified NDT Level II inspector (in lieu of third-party inspection) should consider including this information with the construction documents submitted for approval.
What welds are subject to NDT?
The following summarizes the requirements for NDT inspection requirements contained in the AISC documents.
AISC 360 — Ultrasonic testing (UT) for some complete joint penetration (CJP) groove welds is specified in Section N5.5b. The requirement is based on the type of CJP weld, the risk category of the structure (I, II, III, or IV), and the thickness of the material. In metal buildings, CJP welds are commonly used for flange and web splices, and may also be used for beam to endplates. All of these types of welds could be subject to UT inspection if they also meet the other requirements regarding risk category and thickness.
CJP welds in risk category I buildings are not subject to any UT inspection requirement. In risk category II, III, or IV buildings, UT of CJP welds in materials less than 5/16 in. are not required.
UT must be performed on 100% of the CJP welds (in materials 5/16 in. thick or greater) in risk category III and IV buildings. UT must be performed on 10% of the CJP welds (in materials 5/16 in. thick or greater) in risk category II buildings. AISC 360 Section N5.5f requires that the inspection rate be increased to 100%, where the initial rate for UT is 10%, if the welder or welding operator has a reject rate that exceeds 5%, based on a sampling of at least 20 completed welds on each project prior to implementation of this increase.
AISC 360 Section N5.5e permits the number of inspections to be reduced to 25% if approved by the EOR and building official, where the initial rate for UT is 100%, if the welder or welding operator has a reject rate of 5% or less based on a sampling of at least 40 completed welds on each project. However, as a practical matter, metal building manufacturer weld practices would typically involve a welder working on multiple projects in one shift and tracking this can be a challenge.
AISC 341 — UT requirements for CJP welds is specified in Section J6.2a. The difference between the AISC 341 and AISC 360 requirements is that AISC 341 requires UT on 100% of CJP welds in material 5/16 in. thick or greater regardless of the risk category. However, many risk category I structures are exempt from seismic requirements in ASCE 7, e.g. agricultural buildings, and would therefore not be subject to the requirements in AISC 341.
One key exception that would apply to most metal buildings is that for ordinary moment frames (OMF), in risk categories I or II, UT is only required for demand critical welds. The only demand critical welds for OMF’s are specified as CJP welds of beam flanges to columns in AISC 341, Section E1.6a. So, CJP welds of beam flanges to end-plates are not typically categorized as demand critical. Consequently, for OMF’s, the AISC 360 requirements for the UT of CJP welds would govern.
For intermediate or special moment frames, the UT requirement would apply to all CJP welds in material 5/16 in. thick or greater in seismic force-resisting systems (SFRS) where AISC 341 governs. For intermediate and special moment frames, AISC 358, Prequalified Connections for Special and Intermediate Moment Frames for Seismic Applications, considers a flange-to-end-plate CJP to be demand critical. Note that partial joint penetration (PJP) welds that have been qualified for use for flange-to-end-plate welds for intermediate or special moment frames would not be demand critical nor require UT inspection.
AISC 341 defers to AISC 360 with regard to the reduction in the percentage of CJP welds that need to be inspected. Therefore, the number of inspections can be reduced from the 100% requirement to 25% if the welder or welding operator has a reject rate of 5% or less (sampling of at least 40 completed welds on each project to determine reject rate). This reduction does not apply to demand critical welds.
For more information about the IAS Metal Building Systems Inspection Accreditation (AC472), visit https://www.iasonline.org/services/metal-building-inspection/