Not All Tubular Connections are Welded Equal

by Mike Manor, PE, MLSE
Technical Consultant, Steel Tube Institute
Holly Schaubert, PE
HSS Director, Steel Tube Institute

Hollow Structural Sections (HSS) deliver clean aesthetics, efficient load paths, and an exceptional strength-to-weight ratio — qualities that make them a natural fit for modern steel design. When it comes time to weld those members, however, a common misconception can quietly inflate project cost: the assumption that any connection involving an HSS member automatically requires the most demanding tubular welding qualifications. In fact, AWS D1.1 provides two distinct sets of welding provisions — one for plate connections and one for tubular connections — and many everyday HSS framing connections fall squarely under the simpler plate provisions. Knowing where each set applies is the difference between a routine, cost-effective specification and one that asks the fabricator to chase qualifications the connection geometry doesn’t actually require.  This article walks through how AWS D1.1 distinguishes the two categories, explains what the position designations really mean for the welder, and clarifies which HSS connections genuinely call for the higher-level tubular qualifications. The goal: give designers, engineers, specifiers, and fabricators the confidence to apply the right weld qualification every time.

The first large-scale WAAM application in the construction sector was a footbridge, constructed by the Dutch company MX3D in 2018, to demonstrate the viability of the technology (Figure 1(a)). The stainless-steel bridge was printed in several pieces over a period of six months, then manually welded together. Due to a lack of structural standards for this technology, material, component and full-scale structural testing was carried out, accompanied by modeling, for safety verification (Gardner et al., 2020).

WELDING CODE ORGANIZATION

When first opening the AWS D1.1:2020 code, it is easy to get lost in the language and myriad of figures. As an overview of the code layout, welded connections are primarily split into two categories: tubular and non-tubular connections. The dichotomy can also be considered as welds qualified by plate testing procedures vs. tubular testing procedures. AWS considers tubular members to be pipe, round HSS, or rectangular HSS as well as built-up hollow members. Additionally, AWS defines a tubular connection in Clause 3 as “a connection in the portion of a structure that contains two or more intersecting members, at least one of which is a tubular member.” This definition can be a bit misleading, as some welded connections involving a tubular member can still be qualified by plate testing procedures, as will be described in subsequent sections of this article.

The AWS code’s first eight clauses cover general welding requirements and terminology, with Clause 10 supplementing these with HSS-specific requirements for tubular weld qualification. Each clause is generally organized into three sections: code requirement text, followed by referenced tables, and then figures. The complete weld process encompasses five stages: designing the weld, qualifying both the welder and the weld procedure specification (WPS), installing the weld, and inspecting the finished product. Table 1 in this article provides a roadmap showing which clauses and sections apply to each stage in the weld process.

Table 1: AWS D1.1:2020 Sections for HSS Welded Connections
General Weld Information	Clauses 1, 2, & 3
Weld Design	Clause 4 Parts A, B, & C Clause 10 Part A
Weld Procedure Specification (WPS)	Clause 5 Clause 6 Parts A & B Clause 10 Parts B & C
Welder Qualification	Clause 6 Parts A & C Clause 10 Part D
Fabrication	Clause 7 Clause 10 Part E
Inspection	Clause 8 Clause 10 Part F

WHEN PLATE QUALIFICATIONS APPLY TO HSS CONNECTIONS

From a surface level review of the AWS code, the AWS definition for a tubular connection quoted above would seem to imply that any time a welded connection involves a tubular member, then the tubular weld connection provisions of Clause 10 would be required. However, upon closer inspection of the code, that is not the case. There are several sections that provide additional insight to further refine which tubular connection weld types and locations require the Clause 10 provisions.

First, Section 10.3 titled “Identification and Parts of Tubular Connections” says that “members in tubular structures shall be identified as shown in [AWS] Figure 10.2.” The figure in the AWS code covers three pages showing sketches of various T-connections, Y-connections, K-connections, and cross-connections. A handful of the sketches are presented in Figure 2 of this article. Taking a closer look at the connection sketches, it can be noticed that there is a lack of common connections that involve HSS such as base plates, cap plates, end plates, shear tabs, single angles, double angles, WTs connections, and many more. Since this is consistent with common industry practice, though counter to the AWS tubular connection definition, AISC Design Guide 21 section 14.6.2 offers an alternative definition for tubular connections as “a connection that contains two or more tubular members intersecting in other than an axial orientation.”

Several specific AWS code provisions and commentary sections confirm that plate qualifications are acceptable for many HSS welds. The most relevant are excerpted below; together they clearly demonstrate that the code permits plate qualification for many welding conditions encountered in typical HSS framing without invoking the additional requirements of the Clause 10 provisions.

• Section 6.4 “The production welding positions qualified by a plate test shall conform to the requirements of Clause 6 and Table 6.1.”
  
  
• Section 6.16.1 “The qualified production welding positions qualified by a plate test for welders and welding operators shall be in conformance with Table 6.10. The qualified production welding positions qualified by a tubular test for welders and welding operators shall be in conformance with Clause 10 and Table 10.12.”
  
  
• Section 10.12 “Tubular production welding positions qualified by a tubular test shall conform to the requirements of Table 10.8. Tubular production welding positions qualified by a plate test shall conform to the requirements in Clause 6 and Table 6.1.”
  
  
• Section 10.16.1 “The qualified tubular production welding positions qualified by a tubular test for welders and welding operators shall be in conformance with Table 10.12. The qualified tubular production welding positions qualified by a plate test for welders and welding operators shall be in conformance with Clause 6 and Table 6.10.”
  
  
• Commentary Figure C-6.1 — Type of Welding on Pipe That Does Not Require Pipe Qualification
  “Note: Pipe qualification is not required, and plate qualification is acceptable for groove and fillet welds in the flat, horizontal, vertical, and overhead positions.” — See Figure 3 of this article.
  
  
• Commentary C-10.16 “Welding on pipe (or tubing) material product forms does not necessarily mean that pipe welding is being performed. There is obviously a difference between welding around a pipe as opposed to welding along a pipe parallel to the pipe axis (centerline)…the skills for straight line progression parallel to the pipe axis are no different from the skills for welding plate wrought shapes using a straight line progression…Refer to Figure C-6.1.” — See Figure 3 of this article.

WELD POSITIONS

Welders, and the welding procedures they use to create the welds, are only able to perform welds that they are qualified for. The various weld positions for plate and tubular connections for both fillet and groove weld qualification tests are shown in the accompanying resource called “HSS Welding Position Table,” which is available at this here. Each weld in a connection could need many different qualifications depending on joint geometry and the conditions of how and where the connection is fabricated. When the weld is performed in the shop, there are many options to make the welds easier to install when compared to the field. The members being joined by the weld could be placed on the floor, on a table, upright, lying on its side, or even upside down to make access and position much easier. Each connection is unique based on member geometry and relative orientation which leads to creativity for determining the simplest weld position, and each fabrication shop will have its own preferences and capabilities. The connection could stay in place until all welds are complete, but if there are welds on all four sides of a member, some of the sides will require harder weld positions. Therefore, the member will often be rotated or moved one or more times, when possible, to simplify the weld positions.

Connections in the field, depending on location on the site and ease of access, can (and often do) create much more difficult welding situations compared to the shop. A weld around 4 to 5 feet above the floor line is generally ideal, but rotation is likely not possible. Some welds may need access from a lift before other framing nearby can be added. Thus, in general, greater difficulty of access to a weld that may be in a difficult orientation will increase the welder qualification requirements while also influencing the connection fabrication costs.

To add one more level of complexity, not only does the position of the weld matter, but also the type of weld and type of members being joined. For testing purposes, AWS splits weld types into two broad categories, which are plate qualification and tubular qualification. As discussed in the previous section, just because a tubular section is involved in the welded connection, that doesn’t mean that a tubular qualification is automatically required, as many HSS connections can still use plate qualifications. The qualifications for both plate tests and tubular tests are split into various position tests which are shown in the “HSS Welding Position Table.” The position designations are comprised of a number and a letter, where the number indicates the position for the test and the letter is either F for fillet weld or G for groove weld. The numbers go from 1 to 6, with the first 4 numbers applicable to plate and tubular tests for both fillet and groove welds. The numbers 5 and 6 are reserved for tubular groove welds. As the numbers increase, the difficulty of the weld installation increases.

To bring this altogether in an example, see Figure 4 for a T-connection between two HSS members. In the orientation shown, there will be a mix of weld types on the top, sides, and bottom varying between positions 2, 3, and 4. Alternatively, by rotating the connection after each weld, it could be possible to have a welder qualified at 2F perform all welds of the stepped connection rather than needing a 4F-qualified welder. A second alternative would be to lay the chord down with the branch vertical. In this case, all four side welds can be horizontal (2F) welds, and the welder can move around the joint rather than rotating all the pieces. Clearly, this is the simplest option in theory, but it depends on the size and length of members as well as the shop space available. Note that in the matched connection of Figure 4, a flare bevel groove weld is required on two sides. Now this means that another welder qualification of 3G is required.

TUBULAR WELDS

Tubular welds for T-, Y-, and K- connections on round and rectangular HSS members contain an inherent level of difficulty. To explain why the welds are difficult, some terminology definitions must be discussed first. When there are two steel members welded together, there will be a geometric angle between the two called the dihedral angle, represented by the Greek letter Ψ. For example, two plates in a T-connection perpendicular to each other will have a dihedral angle of 90 degrees. Along the length of the plates, the profile of the weld will consistently be the same. Turning to a Y-connection made of two round HSS members, as shown in Figure 5, there are multiple angles to consider. The branch angle θ is the angle between the centerlines of the two members. At the acute point between the two members along the in-plane axis, called the heel of the connection, the dihedral angle and the branch angle will be the same, thus Ψ = θ. At each point along the weld around the branch, there is a “local” dihedral weld angle that will be larger than the branch angle. The dihedral angle gradually increases from the minimum at the connection heel to a maximum at the connection toe on both sides of the branch. Therefore, when welding the joint, the welder will need to constantly change the amount of weld to lay down as the dihedral angle and intersection profile continuously change. These constantly changing welds are very difficult and take a considerable amount of practice to master.

Rectangular HSS T-, Y-, and K-connections have similar necessary dihedral angle adjustments, but the locations where the change of angle occurs are only in the corners of the branch which is a relatively shorter distance compared to the perimeter of the weld. The rest of the welds on the four sides remain straight. See Figure 6 for a depiction of the toe, heel, side, and transition zones in a matched rectangular HSS connection.

Returning to Figure 5, it depicts the round HSS chord in a horizontal position. However, recall that the weld position is based on the axis of the weld rather than the members being welded. As the line of weld goes around the perimeter of the branch, the location on the chord relative to the top also goes up and down. What if the chord were also at an angle from horizontal? This means that the “weld position” is changing along the line of weld so that some portions of the weld are flat, horizontal, vertical, and overhead; thus, to install the weld, the welder needs competency in all four of these basic positions (1 through 4) in addition to the local dihedral weld constantly changing. To demonstrate these skills, additional weld position tests are required: 5G and 6G. Note that these positions are primarily used for groove welds, as the local dihedral angle in many places around the weld limits the geometry and strength of fillet welds. The weld test for position 5 is a butt weld on a round or rectangular tubular section placed with the axis parallel to the floor (see Figure 7), which remains fixed in place for the entire test. This means the welder must work all the way around the weld joint with a consistent weld while moving in awkward body positions.

With the discussion of the welding difficulty, there is still weld position test 6G. The test setup is similar to 5G except the tubular member is held fixed at a 45-degree angle from horizontal, shown in Figure 7. This increases the difficulty of movement around the member and gravity pulls on the weld pool in a more difficult direction. Per AWS Table 10.12, a 6G qualification covers nearly all tubular connection cases ­— fillet, PJP, and CJP welds on plate, round HSS, and rectangular HSS with one important exception. Rectangular T-, Y-, and K-connections with CJP welds require an additional qualification because tubular CJP weld connections are extremely difficult to install since backing for the weld is hard to place in tubular members. For this reason, one restriction added to the test is that only one side of the connection can be beveled instead of both sides. Additionally, there are times when tubular welds may need to be installed where adjacent framing or the geometry of the connection itself obstructs some of the weld installation accessibility or visibility. To simulate this, a plate ring is placed adjacent to the weld joint, restricting the access to the weld root. The restriction ring adds the R in 6GR, which is considered the ultimate welder test, with this certification covering all other weld positions. 

CONCLUSION

For the majority of everyday HSS framing connections — base plates, cap plates, end plates, shear tabs, single and double angles, WT connections, and similar details — standard plate welding qualifications are entirely sufficient and should be the default. The higher-level tubular qualifications (5G, 6G, and 6GR) are reserved for the specific tubular T-, Y-, and K-connection geometries where the welder must navigate continuously along varying dihedral angles and challenging position changes while working around the joint.  Specifying tubular qualifications beyond where they are genuinely required adds unnecessary cost and can narrow the pool of qualified fabricators without delivering any real benefit. Conversely, both recognizing this distinction early and matching the right qualifications to the right connections, keeps HSS-framed projects on schedule and on budget, delivering structural performance, efficiency, and clean aesthetics.

ADDITIONAL RESOURCES

The following Steel Tube Institute resources provide further guidance on HSS welding design and
specification:

• Welding of Hollow Structural Sections — the foundational primer on HSS weld design, covering fillet weld strength and the implications of one-sided welding.
• Welding in HSS Corners — flare-bevel and flare-V groove welds for full-width and matched-width connections.
• Design of Fillet Welds to Rectangular HSS — effective weld length and weld-size calculation methods.
• Weld Effective Lengths for Round HSS Connections — addresses the gap in code rules for round-to-round HSS joints.
• Full-Capacity Welds: CJP vs. Fillet vs. Fillet-Reinforced PJP — worked design examples weighing the three full-capacity weld options.
• Expert Tips for Cost-Effective HSS Specification and Fabrication — practical guidance on detailing, tolerances, and avoiding costly weld specifications.
• Know Your HSS Welds (Webinar on Demand) — an overview of HSS weld selection and design, with PDH/LU credit available.
• HSS Effective Weld Length Calculator — an online tool for computing effective weld lengths (HSS Professional Membership required).

REFERENCES

1. American Welding Society. AWS D1.1/D1.1M:2020, Structural Welding Code — Steel. AWS, 2020.
2. American Institute of Steel Construction. ANSI/AISC 360-22, Specification for Structural Steel Buildings. AISC, 2022.
3. American Institute of Steel Construction. Steel Construction Manual, 16th ed. AISC, 2023.
4. American Institute of Steel Construction. Design Guide 21: Welded Connections — A Primer for Engineers, 2nd ed. AISC, 2017.
5. American Institute of Steel Construction. Design Guide 24: Hollow Structural Section Connections, 2nd ed. AISC, 2024.
6. Manor, M., and Jacinto, C. “Know Your HSS Welds.” STRUCTURE magazine, February 2024.