Weld Seam Inspection of Steel Structures for Photovoltaic Carports: Standards, Methods, and Acceptan

Weld seam inspection of photovoltaic carport steel structures is a critical quality control process that verifies the safety, load-bearing capacity, and long-term durability of welded connections in solar canopy systems. This article provides a comprehensive technical overview of the welding inspection standards, sampling strategies, non-destructive testing (NDT) methods, and acceptance criteria applied to PV carport steel frameworks, helping project owners, EPC contractors, and manufacturers ensure structural compliance and reliable power generation over a 25-year design life.

Technical Overview

Photovoltaic (PV) carports are dual-function structures that provide weather protection for parked vehicles while supporting solar modules for electricity generation. Unlike ground-mounted PV systems, carport structures carry cantilevered or spanned canopies at heights of 2.5 to 5.5 meters directly above people and vehicles, making structural weld integrity a matter of public safety. The steel frameworks—typically fabricated from Q235B or Q355B structural steel, H-section beams, circular or square tube columns, and cold-formed purlins—transfer dead loads, wind uplift, snow loads, and seismic forces through welded connections.

Weld seams are the most critical and most vulnerable points in these load paths. Defects such as cracks, incomplete penetration, lack of fusion, porosity, and undercut significantly reduce static strength and fatigue life, particularly at column base plates, beam-to-column joints, and cantilever connections subjected to wind-induced cyclic loading. Systematic weld inspection verifies that fabrication meets design drawings, welding procedure specifications (WPS), and the applicable acceptance standards such as ISO 5817, AWS D1.1, EN 1090, and GB 50205/GB 50661. Inspection is typically performed by accredited third-party laboratories or certified NDT personnel qualified to ISO 9712, providing independent documentation for engineering acceptance, insurance, and regulatory compliance.

Why Weld Inspection Is Essential for PV Carports

• Safety-critical location: welded joints are positioned directly above occupied parking spaces, pedestrian walkways, and vehicle traffic lanes.
• Cyclic loading: wind gusts and module vibration create fatigue conditions that can propagate small weld defects into structural cracks over time.
• Thin-walled members: carport structures often use slender tube sections where partial penetration or undersized fillet welds sharply reduce joint capacity.
• Corrosion initiation: surface defects such as undercut, arc strikes, and spatter accelerate corrosion, especially in coastal or high-humidity environments.
• Compliance and liability: documented inspection records support engineering sign-off, building authority approval, insurance underwriting, and warranty claims.

Testing Samples

Primary Structural Welds

These are the main load-bearing connections that receive the highest inspection priority and the largest testing coverage. Typical sample locations include column-to-base plate fillet or full-penetration welds, main beam-to-column connections, cantilever arm welds at fixed-head columns, and spine-beam splices. Full-penetration butt welds in these locations are generally subjected to 100% ultrasonic or radiographic examination, while fillet welds are examined by magnetic particle or penetrant testing on a sampled basis defined by the inspection plan.

Secondary Structural Welds

Secondary samples include purlin-to-rafter connections, module rail attachment welds, bracing member welds, gutter and drainage channel supports, and miscellaneous attachment details. These welds are usually inspected by visual testing with a defined percentage of magnetic particle spot checks, typically 10% to 20%, depending on the specified quality level and structural importance category.

Welding Procedure and Welder Qualification Coupons

Before mass production, test coupons are welded using the qualified procedure to verify the welding procedure specification. These samples undergo visual examination followed by destructive tests including transverse tensile testing, bend testing, macro-etch examination of weld cross-sections, and where required, Charpy V-notch impact testing and hardness testing. Welder qualification test pieces demonstrate that each welder can produce sound welds in the assigned position and joint configuration.

In-Process and Final Production Samples

For serial fabrication, inspection samples are drawn at defined hold points: after fit-up and tack welding, after root passes on full-penetration joints, and after weld completion. Final samples cover completed assemblies prior to hot-dip galvanizing or painting, since coating processes can conceal surface defects and make later inspection more difficult.

Testing Items

Weld inspection programs for PV carport steel structures typically address the following categories of characteristics and defects, classified according to ISO 6520-1:

• Visual and dimensional characteristics: weld size (leg length and throat thickness), weld length, profile and convexity, alignment and mismatch, angular distortion, undercut depth, and excessive reinforcement.
• Surface defects: cracks, surface porosity, incomplete root penetration visible at the surface, lack of side-wall fusion, arc strikes, spatter, and start-stop irregularities.
• Internal defects: internal porosity and gas pockets, slag inclusions, lack of penetration, lack of fusion, and buried cracks detectable only by volumetric NDT methods.
• Mechanical properties on qualification coupons: tensile strength, bend ductility, impact toughness for cold-climate projects, hardness across the heat-affected zone, and macro-structural soundness.
• Material verification: chemical composition and mechanical property verification of base metal and weld consumables to confirm conformity with the design grade.

Testing Methods

A combination of non-destructive testing methods is applied according to joint type, material thickness, accessibility, and the specified acceptance level. All methods are performed by personnel certified to ISO 9712 or an equivalent national certification scheme.

Visual Testing (VT)

Visual testing per ISO 17637 is the first and most widely applied method, covering 100% of all welds. Inspectors use weld gauges, fillet weld rulers, and illuminated magnifiers to evaluate weld size, profile, and visible surface imperfections against the specified quality level. VT is fast, economical, and detects the majority of gross fabrication defects.

Magnetic Particle Testing (MT)

Magnetic particle testing per ISO 9934 is used on ferromagnetic steel components to detect fine surface and near-surface cracks, particularly at weld toes, terminations, and areas around column base plates. MT is highly effective for finding fatigue-critical toe cracks that visual inspection may miss.

Penetrant Testing (PT)

Penetrant testing per ISO 3452 is applied where MT is impractical, such as on non-magnetic attachments, hot-dip galvanized surfaces prepared locally, or complex geometries. PT reveals surface-breaking cracks, porosity, and lack of fusion open to the surface.

Ultrasonic Testing (UT)

Ultrasonic testing per ISO 17640 is the primary volumetric method for full-penetration butt and T-joints with thicknesses typically above 8 mm. UT detects internal lack of penetration, lack of fusion, slag, and cracks. Acceptance is evaluated against ISO 23279 or the contractually specified level, making UT the core method for verifying the integrity of main structural butt welds.

Radiographic Testing (RT)

Radiographic testing per ISO 17636 may be specified for pipe-to-pipe and pipe-to-flange joints where geometric configurations limit UT access. RT provides a permanent photographic record that clearly reveals porosity, slag inclusions, and incomplete penetration.

Dimensional and Coating Verification

Supplementary checks include overall assembly dimensional survey, bolt hole alignment, and after galvanizing, coating thickness measurement to verify durability protection of the welded structure.

Applicable Standards and Acceptance Criteria

The inspection scope and acceptance criteria are defined by the project specification, which typically references the following framework of standards:

• ISO 17635: general rules for NDT of welds in metallic materials, governing method selection and coverage.
• ISO 5817: quality levels for imperfections in welded joints in steel, defining levels B, C, and D; carport structures commonly require level C for general welds and level B for fatigue-critical or full-penetration primary welds.
• ISO 6520-1: classification of weld imperfections for consistent defect terminology and reporting.
• AWS D1.1: Structural Welding Code – Steel, frequently referenced for projects specified in North American practice.
• GB 50205 and GB 50661: Chinese national standards for acceptance of steel structure construction quality and for steel structure welding technology, governing classification of weld grades and inspection percentages for projects under Chinese jurisdiction.
• EN 1090: execution of steel structures, relevant for CE-marked carport components supplied into the European market.
• ISO 3834: quality requirements for welding, defining the welding quality system for the fabricator.

Typical contractual inspection regimes specify 100% VT on all welds, 100% UT or RT on primary full-penetration butt welds, and 10% to 20% MT on primary fillet welds, with secondary welds sampled at lower percentages. Any crack-like indication is rejectable at all quality levels regardless of size.

Applications

Weld seam inspection services for PV carport steel structures are applied across a wide range of project types and project phases:

• Commercial and workplace solar carports at office campuses, factories, hospitals, and educational institutions.
• Public parking facilities at airports, transit stations, shopping centers, and municipal lots.
• Integrated solar EV-charging canopies combining module support with charging infrastructure.
• Distribution and logistics centers covering large parking footprints with standardized canopy units.
• Factory production inspection during serial fabrication, including pre-shipment hold-point verification for exported carport systems.
• Site erection inspection of field-welded connections after installation.
• Periodic in-service inspection and post-storm integrity assessment of operating carport portfolios.

FAQ

Which NDT methods are mandatory for PV carport welds?

Visual testing to ISO 17637 is mandatory for 100% of welds on essentially every project. Beyond VT, the method mix depends on joint type: full-penetration primary butt welds require UT per ISO 17640 or RT per ISO 17636, while fillet welds are verified by MT per ISO 9934 or PT per ISO 3452. The exact percentages are defined in the project inspection and test plan (ITP).

What weld quality level should a solar carport meet?

Most specifications require ISO 5817 quality level C for general structural welds and level B for primary full-penetration welds subject to fatigue or elevated consequence of failure. Under GB 50205 and GB 50661, welds are classified into grades one, two, and three, with first-grade welds requiring 100% NDT and second-grade welds requiring at least 20% volumetric examination.

Who is qualified to perform and certify the inspection?

NDT should be performed by technicians holding ISO 9712 certification in the relevant method and level, working under accredited third-party laboratories or qualified fabricator QC departments. Independent third-party involvement is strongly recommended for engineering acceptance, as it provides impartial reports accepted by design engineers, building authorities, and insurers.

What are the most common causes of weld rejection?

Frequent rejectable findings include undercut exceeding the allowed depth, insufficient or excessive fillet weld leg length, incomplete penetration in full-penetration joints, lack of side-wall fusion, clustered porosity, and slag inclusions. Crack indications of any size are always rejectable and require grinding out and rewelding followed by re-examination.

Can defective welds be repaired?

Yes. Defects are removed by grinding or arc gouging, the excavation is verified by MT or PT to confirm complete removal, and the joint is rewelded under a qualified repair procedure. Repaired welds must then undergo 100% re-inspection using the same or a more sensitive method than originally applied.

How long does inspection of a typical carport project take?

For a standard single-row carport bay, full VT plus sampled MT can typically be completed within a few hours per bay set, while 100% UT of column base butt welds adds time proportional to weld length. Coordinating inspection hold points into the fabrication and erection schedule minimizes schedule impact, and early inspection of qualification coupons prevents costly rework during mass production.

Conclusion

Rigorous weld seam inspection is fundamental to the safe and durable operation of photovoltaic carport steel structures. A well-designed inspection program combining 100% visual testing, targeted surface NDT, and volumetric examination of primary joints—executed by certified personnel against recognized standards such as ISO 5817, ISO 17635, AWS D1.1, GB 50205, and EN 1090—protects the public beneath the canopy, safeguards the 25-year investment in the PV system, and provides the documented evidence required for engineering acceptance and regulatory approval. Project owners are advised to engage accredited third-party laboratories early in the project to define the inspection and test plan and embed quality hold points into the fabrication and erection workflow.