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Visual Testing of Welds for Structural Buildings

Technical and scientific advances over the past century have provided many options for inspecting structural welds when erecting steel-framed structures and buildings. Radiographic Testing (RT), Liquid Penetrant Testing (PT), and Ultrasonic Testing (UT) right through to the most recent advances in phased array are only a few of these technologies. Even with these advances, by far the most common and widely used inspection method for inspecting welds on steel structures is the human eye.

Visual weld inspection is always the first inspection method used to ensure the quality of any weld, and in many, many instances visual inspection is the final means of approval to ensure the integrity and compliance of the weld in question. Nevertheless, as simple as it may sound, just as with many other things in life, there is much more to visual weld inspection than there may seem. There are certain sequenced steps an erector must take and very strict criteria that a responsible steel erector must meet to ensure not only the integrity of the weld being inspected, but also to maintain compliance with project requirements, governing codes, and the steel erector’s own quality control program.

The first step prior to any welding activities being performed on a project is to review the contract documents, which include the erection drawings. These documents will provide you the information of what codes and standards to which the structural steel is to be erected and welded. The erection drawings also provide details of the welded connections. These details will provide the information necessary for determining what prequalified welding procedures will be required for the welding activities or if you need to perform procedure qualification for developing a Welding Procedure Specification (WPS) for a welded joint connection.

Often, after review of the contract documents, it is identified that the steel shall be welded and inspected in accordance with AWS D1.1 Structural Welding Code — Steel, and AISC 360 Specification for Structural Steel Buildings. Within AWS D1.1 and AISC 360, there are requirements for inspection that shall be met by the erector.

Erector’s Responsibility

When reviewing AISC 360, you’ll find Chapter N provides the minimum requirements for quality control (QC), quality assurance (QA), and nondestructive testing (NDT). Quality control in this chapter is defined as provided by the fabricator and erector. AISC 360 N2 requires the erector maintain quality control procedures and perform inspections in accordance with the specification and contract documents. The field welding is to be inspected by the erector’s quality control inspector (QCI). AISC N4 describes the requirements that need to be met for qualification of the QCI.

Weld Inspection Requirements and Frequency

AISC Tables N5.4-1 through N5.4-3 list the inspection requirements for the erector’s QCI. These requirements will either be a perform (P) as defined “perform these tasks for each welded joint or member” or observe (O) as defined “observe these items on a random basis, operation need not be delayed pending these observations.” AISC Table N5.4-1 lists the inspection tasks that must be done prior to welding being performed. Following are the eight items that need to be either performed or observed by the erector’s QCI:

  1. Welding Procedure Specification (WPS) available (Perform).
  2. Manufacturer’s certifications for welding consumables available (Perform).
  3. Material identification (type/grade) (Observe).
  4. Welder identification system (Observe).
  5. Fit up of groove welds (Observe).
  6. Configuration and finish of access holes (Observe). This item is normally a function of the fabricator, but in some cases the erector may have to field fabricate beams.
  7. Fit up of fillet welds (Observe).
  8. Check the welding machine (Observe).

AISC Table N5.4-2 lists the inspection tasks that must be done during welding. Following are the six items the erector’s QCI needs to observe:

  1. Use of qualified welders.
  2. Control and handling of welding consumables; packaging, exposure control.
  3. No welding over cracked tack welds.
  4. Environmental conditions: wind speed, precipitation, and temperature.
  5. WPS being followed: setting on welding machine, travel speed, selected welding materials, shielding gas type/flow rate, preheat, interpass temperature maintained, and proper position.
  6. Welding techniques: interpass and final cleaning, each pass within profile limitations, and each pass meets quality requirements.

AISC Table N5.4-3 lists the inspection tasks after welding. Following are the eight items that need to be examined or performed by the erector’s QCI:

  1. Welds cleaned.
  2. Size, length, and location of welds.
  3. Welds meet the visual acceptance criteria with regard to crack prohibition, weld/base metal fusion, crater cross section, weld profiles, weld size, undercut, and porosity.
  4. Arc strikes.
  5. K-area: inspect for cracks within 3 in. of the weld when welding doubler plates, continuity plates, or stiffeners.
  6. Backing and weld tabs removed when required.
  7. Repair activities.
  8. Document the acceptance or rejection of the welded joint.

Again, the contract documents should be reviewed carefully. The contract documents may stipulate weld inspection requirements that are more stringent than what is listed within AISC Tables N5.4-1 through N5.4-3 and work cannot proceed until the weld inspections are completed by a Quality Assurance Inspector (QAI) and meet the requirement of AWS D1.1 and contract documents. The QCI may not need to perform these inspections but ensure work does not progress until these inspections are complete and in accordance with the contract documents and referencing code. Examples may include but not be limited to the following:

  1. Perform fit up inspections for all complete-joint-penetration (CJP) welds.
  2. Perform root inspection on all CJP welds.
  3. Perform magnetic particle testing (MT) on all root welds of CJP welds.

You may be thinking “where did all these requirements come from?” The answer is they have always been required by AWS D1.1. When reviewing the commentary to the tables listed above in AISC 360, there are references to AWS D1.1 sections for each of these tasks excluding inspection of the K-area. What is useful about these tables is that they are easy to understand and specific to what inspections are required by the erector when welding structural steel in accordance with AISC 360.

To perform the weld inspection tasks required within AISC Tables N5.4-1 through N5.4-3, you will need to reference the following at a minimum: AWS D1.1, Prequalified Welding Procedure Specifications (PWPSs), WPSs, and the contract documents for acceptance criteria.

When the erector’s weld inspector is performing weld inspection, it is important that an inspection procedure be available detailing how to perform the weld inspection. AISC 360 and AWS D1.1 only state what needs to be inspected, frequency of inspection, and acceptance criteria of the item that is to be inspected. The inspection procedure should address but is not limited to the following:

  1. Personnel qualification requirements.
  2. Scope of the procedure.
  3. Use of visual aids.
  4. Light intensity.
  5. Lighting equipment.
  6. Methods or tools for surface preparation.
  7. Distance and angle of the eye to item being inspected.
  8. Sequence of inspection.
  9. Required documentation.

Summary

It is very well defined in the requirements of AISC 360 and AWS D1.1 that weld inspection of structural steel is the responsibility of the steel erector, but it is not overly difficult nor need it be excessively confusing. By following specific sequential steps with properly trained and certified weld inspectors through a sound quality control program, the steel erector can confidently assure the client and the building owner that they are receiving quality welds.