How can you determine whether the installation torque of photovoltaic fasteners meets the required standards? The most direct and reliable method is to conduct on-site testing using calibrated torque measurement tools, combined with scientific installation procedures and comprehensive quality management throughout the entire process. This is not a single step, but a systematic process that spans the entire lifecycle—from selection and installation to acceptance and maintenance. Below, we will address the core question of “how to proceed” step by step, providing you with clear, actionable answers.
How to proceed? First, clear torque standards must be established before installation. These values should not be arbitrarily imagined or set; they must be derived from official technical documents provided by the fastener manufacturer and the PV mounting system supplier. These documents clearly specify the exact installation torque values for bolts of different specifications under various operating conditions (such as steel-to-steel or steel-to-aluminum connections, with or without washers), different surface treatments (such as hot-dip galvanizing or Dacromet), and whether lubricants are used. Contractors must use these as a basis; any approach relying on “feel” or “experience” is an improper starting point. Therefore, the first step—“What to do”—is to strictly obtain and adhere to authoritative torque standard parameters.
What to do? Next, ensure that torque is applied accurately. This depends on using the appropriate tools and correct operating methods. For fasteners in critical areas, preset electric torque wrenches or hydraulic torque wrenches must be used, and the use of uncontrollable impact wrenches should be avoided as much as possible. During operation, the principle of applying force “smoothly and at a constant speed” should be followed to avoid sudden impacts that could cause torque values to exceed limits instantly and damage the threads. For joints requiring multiple bolts, the “cross-symmetrical, step-by-step tightening” process must be adopted. For example, first pre-tighten all bolts to 30% of the standard torque, then tighten to 60%, and finally reach 100% of the standard torque. This ensures even force distribution across the joint surface, preventing component deformation or torque inaccuracies caused by excessive tightening at a single point.
What should be done? Real-time monitoring and recording during installation are critical. This requires the use of professional measuring tools. The most common methods involve using a “torque wrench tester” or a “torque sensor.” Before and during batch installation, perform on-site calibration and testing of the torque wrenches used in construction at regular intervals (e.g., every 4 hours of work or after a certain number of fasteners have been tightened). The specific procedure is as follows: mount the torque wrench on the tester, apply torque, and compare the wrench’s displayed value with the tester’s measured value to ensure the error is within the allowable range (typically ±5%). Additionally, the “marking method” can be used as an auxiliary check: draw a clear, continuous line across the bolt head or nut and the connected component; after tightening, inspect whether the line has shifted due to loosening. However, this method can only qualitatively determine if loosening has occurred and cannot quantitatively assess the torque value.
What should be done? After installation, how do you perform the final compliance verification? At this stage, a torque spot-check is required. Use a calibrated, high-precision “analog torque wrench” or “digital torque wrench” to conduct on-site spot checks. Here is an important concept: the “test torque” is typically set between 90% and 110% of the “installation torque” (specific values depend on the standard). During the operation, apply torque slowly and evenly while observing the wrench reading. If the bolt begins to turn before reaching the minimum value of the original installation torque (e.g., the lower limit of 90%), this indicates insufficient installation torque; if it requires applying torque beyond the maximum value of the original installation torque (e.g., the upper limit of 110%) to turn, this indicates excessive installation torque or that the bolt has seized. Only when the bolt begins to turn within the specified test torque range can the initial installation torque be deemed generally compliant. The sampling rate should follow relevant engineering codes or quality agreements, with a higher sampling rate applied to areas with higher safety requirements.
What should be done? In addition to direct torque measurement, indirect indicators should be used to assist in judgment. Failure to meet installation torque requirements (whether too loose or too tight) will leave traces in the system. Inspect the fasteners and their connection points for abnormalities: for example, check for obvious wear, shearing, or tensile deformation on the bolt threads; check if the nut has been rounded due to over-tightening; check for abnormal indentations or gaps on the surface of the clamped components; and, particularly for aluminum alloy components, check for cracks caused by over-tightening. If abnormal noises or visible displacement are detected at certain joints after the PV mounting system is subjected to wind loads, this is often related to loose fasteners. These signs can serve as indicators that there may be issues with the torque.
What should be done? It is essential to recognize the impact of the environment and time and establish a long-term assessment mechanism. Since photovoltaic power plants are located outdoors and are constantly exposed to wind vibrations, thermal expansion and contraction, and corrosion, torque values may deteriorate over time. Therefore, determining whether torque remains “consistently within specifications” is equally important. This requires regular O&M inspections. During O&M, in addition to using torque wrenches for periodic (e.g., annual or biennial) torque re-checks, more advanced equipment such as “ultrasonic bolt stress testers” should be widely utilized. This equipment precisely calculates the axial preload by measuring changes in the propagation time of sound waves through bolts under load. Its assessment results are more scientific than simple torque measurements because they eliminate the influence of fluctuating friction coefficients and directly reflect the “clamping force”—the most critical aspect of fasteners.
What should be done? Finally, and most importantly, all of the above methods must be systematized and documented. Establish a comprehensive torque quality control process covering the entire chain: “standard acquisition → tool calibration → process training → process monitoring → completion verification → operational review.” Each stage should be documented to form a traceable quality record. For example, calibration records for every installation wrench, torque spot-check data for every critical node, and reports from every routine inspection. Only through systematic management can we ensure that “determining whether torque meets standards” is not a temporary, isolated action, but rather a verifiable, continuous, and reliable routine operation.
In summary, determining whether the installation torque of PV fasteners meets standards requires a multi-pronged approach: guided by standards, measured with precision tools, grounded in standardized processes, protected by process monitoring, supplemented by periodic reviews, and underpinned by systematic management throughout. Only in this way can we ensure that every fastener is truly secure, laying a solid foundation for the safe and stable operation of photovoltaic power plants over the next 25 years.
