Main Processes in the Fabrication of Steel Structural Components for Buildings

As modern society and the economy continue to develop, people’s quality of life is steadily improving, and human living environments, housing conditions, and residential needs are constantly evolving. With increasingly stringent state control over land-use systems—particularly in Shenzhen, where building land has become ever more scarce—structures are trending toward ultra‑tall designs. Reinforced concrete can no longer adequately meet the demands of architectural efficiency, structural performance, design flexibility, or certain specialized functional requirements. Steel structures, owing to their light weight, high strength, excellent ductility and toughness, ease of fabrication, and short construction timelines, have been widely adopted in high‑rise buildings, and today, the structural systems of such buildings are increasingly shifting toward steel‑based solutions.

I. Introduction:

Since steel‑structure projects typically serve as the core and load‑bearing components of high‑rise buildings, their quality directly affects the structure’s safety, structural integrity, and durability. Poor quality can, at best, impair normal use; at worst, it may result in substantial economic losses and severe casualties. Consequently, steel‑structure construction is classified as a specialized engineering discipline, and both national and local construction authorities attach great importance to its quality, having accordingly formulated and promulgated numerous codes, standards, and technical specifications covering all aspects of the work. Over the years, many experts in the field have devoted themselves to research in this area, producing a wealth of monographs and scholarly publications from diverse perspectives, thereby making significant contributions to steel‑structure engineering—spanning everything from design and construction to the application of new processes and technologies.

In recent years, the development of the construction industry has been plainly evident. Construction projects are no longer merely spaces that fulfill people’s needs for work, living, and housing; they have also become a highlight of urban development and an integral part of the cityscape. As urban land is extensively developed and land resources grow increasingly scarce, high-rise buildings have emerged as the mainstream trend in urban development and a defining feature of modern cities. With the growing prevalence of high-rise structures, steel‑structure engineering has increasingly leveraged its advantages—rapid construction, short project timelines, reduced formwork usage, high strength, swift execution, and ease of prefabrication and installation—leading to its broader application across various projects. In response, the state has formulated relevant standards such as the “Code for Quality Control and Acceptance of Steel Structure Construction” and the “Code for Welding of Steel Structures,” while industry experts and scholars have also established sector‑specific and enterprise‑level standards. For example, China State Construction Engineering Corporation has issued guidelines like the “Steel Structure Fabrication Process.” Despite the promulgation and implementation of these standards and regulations, steel‑structure projects continue to encounter a range of issues, including cracking and paint‑coating delamination on component surfaces. While only a small fraction of these problems can be traced back to raw materials—since material defects directly compromise the safety and serviceability of the structure—the vast majority stem from deficiencies in fabrication, processing, and on‑site installation. Addressing the persistent quality challenges in steel‑structure projects is a complex, system‑wide undertaking that demands meticulous attention at every stage of the construction process, among all stakeholders, and throughout every design and construction phase. At the same time, efforts to promote and apply new steel‑structure technologies and innovative construction methods must be significantly intensified, ensuring that the public fully appreciates the critical role steel‑structure engineering plays in enhancing people’s living conditions, daily life, and working environments. Only through such concerted efforts can we effectively mitigate and ultimately eliminate these recurring quality issues.

II. Analysis of Quality Problems in Steel Structure Engineering

There are numerous and complex reasons why the quality of steel‑structure projects is difficult to ensure. These include issues arising from improper fabrication processes, violations of procedural guidelines, deficiencies in the technical expertise and sense of responsibility of construction personnel, and quality problems caused by decision‑making errors. This paper primarily analyzes the most common problems that occur during the fabrication of architectural steel structures, with the hope that readers will gain some useful insights.

(1) Problems inherent in the steel material itself

During the fabrication of 1200×1200×60 box columns for a certain building, welders unexpectedly observed tearing in the 60‑mm‑thick web plate. Visible cracks clearly bisected the plate through its thickness. NDT inspection revealed that the crack depth was approximately 3 mm. Further examination of cut components from several other plates of the same type and batch identified delamination within the material; poor rolling quality was identified as the primary cause of this defect. During welding, the residual stresses generated by the process further propagated the delaminated layers, resulting in the observed tearing of the thick plate along its thickness direction.

　　Cause analysis: Due to the specific service conditions, this component serves as a web in the structure. The longitudinal welds—both top and bottom—are made using full‑penetration groove joints on stiffening plates subjected to loading. Because of delamination within the plate, the welding stresses generated during fabrication are released outward, leading to tearing of the plate along its thickness direction.

The following measures may be adopted based on the actual circumstances:

(1) The numerous internal delaminations in the steel are quality defects originating during the rolling process at the steel mill, exceeding the requirements of national standards. You may request that the steel mill dispatch personnel to verify the issue and negotiate with them for a return or replacement.

(2) If the number of interlayers is small, solicit input from the technical department and the owner, relay this information to the steel mill, and implement corrective measures during construction. Based on the results of nondestructive testing, completely gouge out any defective areas to a depth exceeding the original thickness, then fill these areas with weld material of equivalent strength. Following completion, perform surface treatment and, after the prescribed interval, conduct NDT inspection. Simultaneously, take samples from identical components for physicochemical testing; if the results meet the design code requirements, the component may continue in service.

(3) Under the supervision of the supervising engineer, cut out the component and replace it with a plate that meets the required specifications. The removed component shall be reused in non-load-bearing or non-critical areas or repurposed as auxiliary material. Upon completion, perform NDT inspection within the prescribed time frame and maintain appropriate records.

Corrective actions that can be taken and measures to prevent similar quality issues:

(1) When entering into steel procurement contracts, specifying nondestructive testing requirements for the purchased steel will increase procurement costs. However, this approach effectively prevents and mitigates potential financial losses at the source.

(2) For steel plates that have already been purchased but have not yet entered the production process, 100% NDT inspection shall be conducted at the material storage yard prior to cutting. This measure aims to prevent losses that might otherwise occur during the cutting and machining stages, thereby containing such losses before the materials are incorporated into the production flow.

(3) Conduct Z-direction property tests and physicochemical tests on thick plates intended for special applications and specific locations, and approve the material quality.

(4) Prepare appropriate process documentation. During welding, particularly for medium- and thick‑plate joints requiring full penetration, implement sound fabrication and machining procedures. The technical department shall finalize the welding procedure prior to commencement and provide on‑site process guidance. The quality inspection department should strengthen on‑site supervision and verification, with particular emphasis on monitoring and controlling welders’ technical competence, welding orientation, sequence of passes, heat‑preservation measures during welding, interpass temperature control, and other critical factors. Comprehensive preventive measures must be adopted to mitigate welding defects arising from the welding process.

(II) Issues Arising During the Construction Process

The typical fabrication process for steel structures is as follows: layout → cutting → end milling → drilling → straightening → assembly → welding → re‑straightening → grinding → rust removal → painting → stacking, and so on.

In accordance with national codes, technical standards, and the supervising engineer’s requirements for steel structures, and drawing on nearly ten years of on-site experience in steel‑structure construction, the processes most prone to quality issues—and whose subsequent rectification is particularly challenging—are the special and critical procedures. By contrast, quality problems in routine operations account for only a small proportion. In the aforementioned construction process, the special procedures include welding and coating, while the critical procedures comprise material cutting and assembly.

1. Welding process. This process is classified as a concealed work and is one of the most prone to quality issues. According to product quality reports from a certain company in 2004, among the quality problems encountered in this process: weld‑seam rework due to welding quality accounted for over 80%, while weld‑seam defects caused by improper operations in the preceding process or operator‑related technical deficiencies made up approximately 10%. Such issues directly impact the overall project quality; therefore, they can only be detected and evaluated by specialized inspection firms using professional testing equipment. Typically, weld‑seam defects are categorized according to their nature, including slag inclusion, lack of fusion, and porosity.

Cause Analysis:

(1) In X‑groove full‑penetration welds, incomplete root cleaning on the reverse side during welding can lead to quality defects in the weld.

(2) In V‑groove welds employing backing strips, if the oxide scale, rust, oil, or other contaminants on the surface of the backing strip adjacent to the weld are not thoroughly cleaned or are only partially removed, and welding is performed directly on this surface, subsequent instrumental inspection reveals quality issues at the backing‑strip location.

(3) Due to inadequacies in the preparation of process documentation—such as insufficient workspace in confined welding positions, weld groove dimensions that fail to meet construction requirements, welding currents that do not comply with specified parameters, irreversible distortion caused by improper welding procedures, and the omission of preheating for medium- and thick‑plate materials, coupled with inadequate heat‑preservation measures and improper interpass temperature control during welding—various issues may arise.

(4) During the welding of structural components, inadequate welding methods fail to meet the required weld quality standards. For example, when manual root pass welding is employed but the weld quality itself does not satisfy the specifications, an automatic submerged-arc welding cap pass is subsequently performed. Additionally, the flux‑cored wire and flux used in automatic submerged-arc welding are not properly baked or subjected to temperature control as prescribed. Furthermore, insufficient operator accountability can lead to surface defects in the weld.

The following measures may be adopted depending on the specific circumstances:

(1) Prepare accurate process documentation; in particular, for components fabricated by welding medium‑ and thick‑plate materials, develop corresponding welding procedure qualifications tailored to the specific structural characteristics of the project, maintain meticulous records throughout the testing process, and accumulate valuable experience for future construction. Dimensions of groove preparations, required joint gaps, and other parameters shall be determined strictly in accordance with national standards. Ensure that the prepared process documents are accurate, practical, cost‑effective, and appropriately suited to the intended application.

(2) The selection of welding consumables shall be determined in accordance with welding procedure qualification tests and relevant national standards. During fabrication, strict adherence to national standards is required for pre-use storage and post‑use baking; the holding temperature must be maintained within the limits specified in the applicable codes and standards.

(3) During the assembly and welding process, surface contaminants such as rust, oil, and oxide scale must be thoroughly removed to ensure proper preparation of the base metal and to guarantee high-quality welds. Adequate surface treatment of the welding base metal is essential.

(4) On the reverse side where root cleaning is required prior to welding, thorough and meticulous cleaning must be performed to ensure that the weld meets the design specifications.

2. Painting process. This process is also a concealed operation, with its impact on the structural integrity being less significant than its effect on the building’s functionality. It is also one of the processes most prone to quality issues. The main quality problems in this stage include: large‑area or localized peeling of the paint film on component surfaces; peeling and sagging of the paint film; insufficient paint film thickness; uneven thickness distribution; and significant color variations in the paint film.

Cause Analysis:

(1) The substrate preparation on the component surface was inadequate, with residual rust, oxide scale, or oil contamination, failing to meet the required surface roughness specifications. This resulted in poor adhesion, particularly in projects with stringent coating requirements, where components must comply with both process and design specifications.

(2) Due to the level of construction technology, the adopted construction methods are relatively outdated, relying on manual techniques such as brushing and roller application. This results in uneven paint film thickness, and subsequent touch-up work performed before or after completion leads to significant color variations.

(3) During construction, prevent quality issues arising from objective factors such as weather conditions or improper operator practices—for example, when on-site temperature and humidity levels exceed specified limits, or when components are inadequately protected.

(4) Serious violations in paint application resulting from rushed schedules and aggressive task deadlines can give rise to significant quality risks and compromise both product quality and safety.

The following corrective and preventive measures can be implemented to address and prevent quality issues and to avert potential problems:

(1) Prior to the commencement of each project, conduct a process qualification test using coating specimens to determine the appropriate surface treatment measures and verify the accuracy and operability of the associated process documentation, including coating film thickness, the time required for complete drying and surface dryness, as well as the influence of and control over ambient temperature.

(2) Ensure compliance with the specified intercoat waiting times and total coating thickness for the primer, intermediate coat, and topcoat layers. Carry out application strictly in accordance with the manufacturer’s instructions to prevent adverse reactions between different coating components that could compromise the final coating quality.

(3) Prior to coating, the surface preparation by sandblasting must meet the specified quality requirements. Before applying the paint, all sand particles, burrs, and any areas requiring masking must be properly masked as required. Coating of the component surface must be carried out no later than two hours after completion of sandblasting.

(4) Components that have just been coated must be protected against rain, windblown sand, and dust to prevent surface contamination and maintain their aesthetic quality.

(5) During the spraying process, avoid stacking the component with other engineering elements of different colors to prevent cross-contamination caused by the migration of coating components.

(6) After completing the work, promptly clean and maintain all painting tools and equipment.

3. Layout and cutting process. This process serves as the initial step in component fabrication, and its quality directly impacts subsequent operations—potentially even resulting in the scrapping of all cut parts. Such occurrences are quite common; therefore, strengthening quality control during this stage is both critical and essential. The primary quality issues arising in this process include: significant deformation of long‑strip and thin‑plate components during cutting; the appearance of burrs, nodules, or excessive cut‑mark depth on the cut surfaces due to impurities in the cutting gas or uneven material composition; dimensional deviations in gas‑cut or sawed parts caused by failure to account for shrinkage during downstream operations; batch‑level scrap resulting from errors in the preparation of process documentation; and severe dimensional overruns that fail to meet specified tolerances.

Cause Analysis:

(1) The purity of the cutting gas fails to meet the required specifications, resulting in quality issues on the cut surface.

(2) Due to the sudden exposure of steel surface scale to high temperatures, it can spall and clog the cutting torch, resulting in cutting quality issues such as a jagged or serrated edge.

(3) Due to the skill level of the operators, manual cutting has resulted in quality issues such as non‑straight cut lines and inclined cut surfaces.

(4) Due to uneven stress distribution, elongated components develop a saber‑shaped bend.

(5) It is related to the operating machinery’s tracks, as well as the degree of use and precision of the instruments. For example, during the cutting process, if the cutting equipment has been in service for a long time, issues such as vibration and bouncing during movement can adversely affect the cut quality.

The following corrective and preventive measures can be implemented to address and prevent quality issues and to avert the emergence of potential problems:

(1) Prior to mass production of component layout, conduct thorough random inspections to prevent large-scale, irreparable rework. For templates and tooling used in the fabrication of complex components, implement a rigorous oversight and inspection system to identify and address issues before material cutting begins.

(2) Strengthen process monitoring and rigorously implement the “three‑inspection system” of operator self‑inspection, team leader mutual inspection, and dedicated inspector’s specialized inspection. Maintain thorough process records to oversee compliance, ensuring that the three‑inspection system is not merely a formality.

(3) Prior to formal cutting, ensure proper preheating to prevent sudden spalling of oxide scale on the steel surface during the cutting process, which can clog the cutting nozzle and introduce defects in the cut surface, thereby avoiding the need for subsequent repair and grinding.

(4) Wherever possible, employ automated and semi-automated processes to minimize manual operations and reduce the occurrence of human error.

4. Assembly Process. This process plays a critical role in the quality of component fabrication, and its outcomes are heavily influenced by the preceding operations; therefore, rigorous process monitoring prior to assembly is essential. The primary quality issues arising in this stage include: incorrect positioning of assembled components—for example, a 3,450 mm dimension being installed as 4,350 mm; misuse of parts—such as installing a No. 3 component instead of the intended No. 2 part; improper installation of components in their designated locations—for instance, mounting a 45 mm hole on a plate facing inward rather than outward; assembly gaps exceeding the tolerances specified in standards and technical documentation—e.g., a 3 mm gap now measuring 7 mm; assembly of components without prior alignment, resulting in residual deformation that cannot be corrected after completion; unauthorized cutting by operators to simplify procedures, leading to out‑of‑tolerance hole dimensions; lack of surface treatment in weld‑assembly areas; and assembly errors caused by dimensional inaccuracies in the design drawings.