Comparative Analysis of Electrostatic Charging Characteristics Considering the Flow Conditions of Nonconductive Flammable Liquids

Abstract

Electrostatic is generated through friction or contact between certain materials—a process that frequently occurs in industries such as manufacturing, logistics, electronics, chemicals, petroleum, and gas. In particular, in industries dealing with flammable materials—such as petrochemicals, refining, energy, semiconductors, and electronics—electrostatic can pose a fire or explosion risk, highlighting the critical importance of implementing electrostatic control and preventive measures. To manage electrostatic at a safe level, it is crucial to prevent charge accumulation that would lead to high charging voltages. This study developed a streaming electrification generator that considers the flow conditions of non-conductive flammable liquids, allowing observation, comparison, and analysis of electrostatic charging characteristics. Specifically, to determine conditions that create fire and explosion hazard atmospheres, measurements of charging voltage, discharging current, and charging electric charge were obtained and analyzed under various experimental conditions. A comparative analysis of various electrostatic charging characteristics revealed that, in certain cases, increasing the temperature of a flowing liquid may actually decrease the charging voltage depending on the properties of the pipeline material. By considering not only the decrease in liquid conductivity with temperature changes but also the variation in the work function of solid materials, the underlying causes of the observed results can be understood. The experimental results derived from this study provide concrete and reliable data essential for controlling and managing electrostatic at a safe level and are expected to serve as a foundational resource to more clearly identify electrostatic risks in industrial safety management.

1. Introduction

Globally, companies in the petrochemical, refining, and energy sectors are increasingly directing their investments toward industries related to batteries, bio- and renewable energy materials, plastic and waste battery recycling, and hydrogen energy. With a rising demand for new chemicals whose hazards are not fully understood, particularly in the petrochemical, oil refining, energy, semiconductor, and electronics industries, the need for handling flammable liquids and gases with high electrostatic hazards is also expected to grow [1]. In fact, in processes such as semiconductor manufacturing, display production, PCB substrate fabrication, and chemical vapor deposition, various types of flammable liquids and gases are handled and used as catalysts for chemical reactions. As a result, there is an ongoing risk of fire and explosion, with electrostatic serving as a potential ignition source [2,3].

Electrostatic fires and explosions are typically caused by the interaction of multiple causal variables, rather than by a single causal factor acting independently [4]. The charging and discharging of electrostatic is characterized by unpredictability and limited reproducibility, highlighting the importance of experimentation and analysis in various situations to improve safety management practices.

In other words, although the probability of electrostatic fires and explosions is low, the potential risk is extremely high in industries such as petrochemicals, refining, energy, semiconductors, and electronics. Therefore, it is essential to implement proactive measures to control electrostatic and maintain it at safe levels, especially in areas vulnerable to fires and explosions. However, in Korea, surveys of industry professionals and analyses of comments from disaster investigations indicate a perceived lack of technical infrastructure to identify the mechanisms of electrostatic generation at industrial sites, as well as insufficient quantitative data [5].

The authors in Ref. [6] evaluated electrostatic ignition hazards associated with handling flammable gases, liquids, and powders in industrial settings. In Ref. [7], the research examines regulations and testing for electrostatic charge separation and discharge risks at self-service fuel stations, emphasizing safety protocols, relevant equipment, and preventive practices for fire hazards. However, specific considerations regarding the flow dynamics of flammable liquids were not addressed in Refs. [6,7]. The authors in Ref. [8] conducted experiments on electrostatic generation due to friction between liquids and solids, and they proposed a new streaming electrification model, but it is limited in that the experimental objects and conditions were limited and only charge density analysis was performed. In Ref. [9], an electrohydrodynamic model was proposed to analyze the electric fields above the surface of charged liquids, and it was confirmed that the charge accumulation on the liquid surface decreases with increasing flow velocity. In contrast, we expand the analysis by examining not only flow rate but also the effects of temperature, pipe length, and material, with a focus on total charge and charging voltage rather than charge distribution.

In addition, recent studies share a commonality with this research in that they address the causes and processes of electrostatic generation and its associated risks [10,11,12,13]. The authors in Ref. [10] focus on practical safety measures and organizational strategies for managing electrostatic hazards during diesel fuel handling, emphasizing operational best practices. Meanwhile, Ref. [11] delves into charge transfer in electrostatic discharges (ESD), examining capacitance evaluation and hazard assessment to provide a detailed understanding of discharge characteristics. In contrast, this study investigates streaming electrification in non-conductive flammable liquids, exploring how flow conditions, material properties, and temperature variations influence charge generation. This experimental work offers insights into dynamic charging processes and the underlying physical mechanisms contributing to electrostatic hazards.

The study investigates electrostatic hazards in material web processes, emphasizing the measurement of electric fields, charge distributions, and the optimization of ionizer placement to mitigate risks, including phenomena like “super brush discharge” [12]. While it offers valuable insights into electrostatic mitigation in solid material systems, its focus differs significantly from this study, which targets streaming electrification in liquid systems, specifically non-conductive flammable liquids. In contrast, the study aligns more closely with this research, as it also explores streaming electrification in liquids [13]. However, the study focuses on insulating liquids to enhance transformer reliability by mitigating electrostatic risks, whereas this study prioritizes industrial safety, examining conditions that create fire and explosion hazard atmospheres. By analyzing the effects of flow conditions, temperature, and material properties, this study extends the understanding of streaming electrification to address critical safety challenges in industries handling flammable liquids.

This study contributes a novel approach to understanding and managing electrostatic risks in industrial settings by developing a streaming electrification generator that accounts for flow conditions of non-conductive flammable liquids. Through comprehensive measurement and analysis of charging voltage, discharging current, and electric charge under varied conditions, the study provides valuable insights into the effects of temperature and pipeline materials on electrostatic characteristics. Specifically, it reveals how temperature and material properties influence electrostatic behavior, providing a deeper understanding of conditions that affect charging risks.

This paper is organized as follows: Section 2 discusses the non-conductive flammable liquid, the subject of this study, and provides the theoretical background of the research methodology employed. Section 3 describes the experimental apparatus and methods used, while Section 4 presents the experimental results, considering various flow conditions of the flammable liquids. Section 5 concludes with a summary of key findings and their implications for safety management practices.

2. Subject Material and Theoretical Background

2.1. Subject Material

In this study, we aimed to verify the electrostatic properties of diesel oil, a non-conductive flammable liquid, by examining its electrostatic characteristics. Diesel was chosen due to its involvement in numerous significant industrial disasters, as demonstrated by an analysis of reports on major disasters and industrial accidents related to electrostatic fires and explosions from 2012 to 2021. These reports show that flammable liquids accounted for 60.3% of the 63 incidents. When hybrid materials are included, this figure rises to 77.8% [5].

Table 1. The Electrostatic Characteristics of Flammable Liquid [4].

Liquid	Conductivity (pS/m)	Dielectric Constant	Relaxation Time Constant (s)	Minimum of Ignition (mJ)
Diesel	0.1	2	100	20

below presents the conductivity, dielectric constant, relaxation time, and minimum ignition energy of the target material, diesel oil.

2.2. Theoretical Background

When a liquid flows through a pipe, electrostatic is generated between the liquid and the pipe wall. When a sieve contacts a solid material, such as a pipe, an electric double layer forms at the liquid-solid interface, generating electrostatic as some of the charge moves with the flowing liquid. In this process, the primary factor influencing electrostatic generation is the flow rate of the liquid; however, it is also affected by the liquid’s conductivity and temperature, as well as the material, diameter, and curvature of the pipe [14].

If the electrostatic discharge energy exceeds the minimum ignition energy of flammable liquids, a fire or explosion may occur. In such cases, the electrostatic discharge energy can be calculated using the following equation, which is a function of the electrostatic potential, the amount of electrostatic charge, and the capacitance of the charged object [15].

$$W={\displaystyle \frac{1}{2}}QV={\displaystyle \frac{1}{2}}C{V}^2={\displaystyle \frac{1}{2}}{\displaystyle \frac{Q^2}{C}}\left[\mathrm{J}\right],$$

(1)

where, W is the electrostatic discharge energy (J), V is the electrostatic potential (V), Q is the electrostatic charge (C), and C is the capacitance (F).

Therefore, by measuring the electrostatic potential and the charge amount of electrostatically charged objects, the electrostatic discharge energy can be calculated and compared with the minimum ignition energy, providing a basis for assessing the risk of fire and explosion. Such measurements, particularly of the potential and electric charge of objects during the processing and transfer of flammable liquids, enable an empirical assessment of the likelihood of electrostatic discharge in a fire and explosion hazard atmosphere. Additionally, from an electrostatic risk assessment perspective, periodic monitoring of electrostatic potential, electric charge amount, and discharge current in hazardous areas can further enhance safety management.

2.3. Background of Electrostatic Measurements

The electrostatic potential is measured by positioning a detection electrode in front of the charged object and recording the potential generated on its surface [15]. In this measurement technique, the electrostatic potential of the charged object is assessed by dividing it into detection electrodes. It is further categorized into capacity split and resistor split methods, depending on the the split method used.

First, the capacity split method is shown in Figure 1a. In this method, the surface potential of the charged object is measured by dividing the capacitance using the detection electrode. Here, $C_1$ represents the capacitance between the charged object and the detection electrode, while $C_2$ represents the capacitance between the detection electrode and the ground. The relationship between the surface potential of the charged object and the potential of the detection electrode can be expressed as the Equation (2).

$$V_s=(C_1+{\displaystyle \frac{C_2}{C_1}})V_d.$$

(2)

Second, the resistor split method measures the surface potential of the charged object by dividing the resistance using the detection electrode, as shown in Figure 1b. In this method, $R_1$ represents the resistance between the charged object and the detection electrode, and $R_2$ represents the resistance between the detection electrode and the ground. The relationship between the surface potential of the charged object and the potential of the detection electrode can be expressed as the Equation (3) [15].

$$V_s=\left({\displaystyle \frac{R_1+R_2}{R_2}}\right)V_d.$$

(3)

The electrostatic charge is measured using an insulated metal container known as a Faraday cage. The principle of measurement with the Faraday cage is shown in Figure 2, where a measuring capacitor is used to reduce the potential of the Faraday cage. In the equivalent circuit depicted in the following figure, the electric charge of the charged object can be calculated from the potential measurement using the Equation (4) [16].

$$Q=(C_f+C_0+C_{in})V,$$

(4)

where, $C_f$, $C_0$, and $C_{in}$ represent the capacitances of the Faraday cage, the measuring capacitor, and the electrostatic meter, respectively.

The electrostatic discharging current can be measured by connecting an electrometer to observe the discharge characteristics when a charged object is connected to a grounded object. To ensure accurate measurement, an electrostatic shielded steel mesh is used to block airborne charges. When charge is induced on the pipe through electrostatic induction, grounding allows this accumulated charge to discharge, enabling the measurement of the resulting discharging current [17].

3. Experiment Procedures

Configuration of Experiment Instruments

The electrostatic charge experiment instruments for flammable liquids consists of a control panel, a transferring device, and a piping system. The control panel includes a static potential monitoring system, an electrometer, and a recorder, as shown in Figure 3. The specifications of the instruments used to measure electrostatic generation in flammable liquids are provided in

Table 2. The instrument for measuring electrostatic.

No	Meter	Model	Characteristic
1	Voltage	KSR-1001	0–±50 kV, Exia, 10 ch
2	Current	Keithley 6514	20 pA–200 μA
3	Coulomb	NK-1002	±1–9, 999 nC
4	Faraday Cage	KQ-1400	Cup size: 100 mm * 100$\varphi$
5	Pressure	P601EX	0–10 bar, Exd
6	Flow	FT210-VM	0–20 L/min, Exd
7	Temperature	T300EX	0–100 °C, Exd

.

The transfer device includes a tank for transferring and recovering flammable liquids, a heater to control the temperature of the liquids, a valve, a transfer pump, a pressure gauge, and a flow meter, as shown in Figure 4. Additionally, the piping system is designed to vary the material, diameter, and length of the pipes for each experimental condition, incorporating findings from previous studies and literature, such as disaster investigation analyses, to create different flow conditions, as illustrated in Figure 5 [14,16,18].

The experimental procedure for the comparative analysis of electrostatic charge characteristics is outlined in Figure 6. First, the electrostatic charging voltage is measured by circulating the flammable liquid in the piping system with the pump running for 90 s, allowing electrostatic charge to accumulate. Second, at 60 s after the pump starts, the discharging current is measured for 30 s by grounding the piping system. Third, at 90 s, the pump is stopped to end liquid circulation. From this point, the valve is closed to observe the electrostatic dissipation characteristics, and the charging voltage and discharging currents are continuously measured in the system with stationary liquid for 150 s. Finally, the electric charge of the flammable liquid is measured for 210 s after the pump is stopped to observe static dissipation characteristics.

The time lengths were determined based on preliminary experiments to capture key trends in charging voltage behavior, discharge current characteristics, and electrostatic relaxation. These durations were selected to ensure the accurate observation of critical phenomena while considering safety and experimental guidelines.

4. Experiment Results

4.1. Experimental Hypotheses

The experimental hypothesis is that electrostatic generation is influenced by variables such as the material, diameter, and length of the pipe through which the flammable liquid flows, as well as the transferring pressure, flow rate, and temperature of the liquid. It is hypothesized that, due to their relatively high conductivity and dielectric constant, PVC (Polyvinyl Chloride) pipes will generate more electrostatic than PE (Polyethylene) or PP (Polypropylene) pipes, especially as the pipe diameter decreases or the length increases. Additionally, an increase in flow rate is expected to raise electrostatic levels due to increased friction between the liquid and pipe surfaces, which enhances charge separation. A rise in liquid temperature is assumed to reduce conductivity, leading to greater static charge accumulation. To test these hypotheses, various conditions for generating electrostatic charge were established.An experimental device was then constructed to systematically observe and analyze the resulting electrostatic charge characteristics under varying flow rates, temperatures, and pipe materials.

4.2. Data Analysis of Electrostatic Measurement

Table 3. Experiment conditions.

Case	Pipe			Flammable Liquid
	Material	Diameter	Length (m)	Pressure	Flow Rate (L/min)	Temperature (°C)
1	PP	16A	3.18	0.07 bar	1.646	18.8
2	PE	16A	3.40	0.07 bar	1.121	19.2
3	PVC	16A	3.58	0.07 bar	1.936	19.5
4	PP	16A	3.18	0.12 bar	3.867	19.0
5	PE	16A	3.40	0.12 bar	3.941	18.8
6	PVC	16A	3.58	0.12 bar	3.786	19.6
7	PP	Multi	2.54	0.07 bar	1.735	19.3
8	PE	Multi	2.69	0.07 bar	1.019	18.7
9	PVC	Multi	2.84	0.07 bar	1.109	19.3
10	PP	Multi	2.54	0.12 bar	3.645	18.9
11	PE	Multi	2.84	0.12 bar	3.705	18.5
12	PVC	Multi	2.69	0.12 bar	3.956	19.0
13	PP	16A	3.18	0.07 bar	0.328	29.7
14	PE	16A	3.40	0.07 bar	0.138	29.5
15	PVC	16A	3.58	0.07 bar	0.027	30.0
16	PP	16A	3.18	0.12 bar	3.414	31.2
17	PE	16A	3.40	0.12 bar	3.058	31.4
18	PVC	16A	3.58	0.12 bar	3.605	30.0
19	PP	Multi	2.54	0.07 bar	0.041	29.6
20	PE	Multi	2.69	0.07 bar	0.481	30.6
21	PVC	Multi	2.84	0.07 bar	0.388	29.3
22	PP	Multi	2.54	0.12 bar	3.776	30.7
23	PE	Multi	2.84	0.12 bar	2.976	31.9
24	PVC	Multi	2.69	0.12 bar	2.831	32.0

below summarizes the measured values of charging voltage, discharge current, and the amount of electrostatic charge for each experimental condition.

Table 4. Electrical and physical characteristics by pipe type.

No	Item	PVC	PE	PP
1	Volume Resistivity (Ω/cm)	${10}^{12}$	${10}^{18}$	${10}^{18}$
2	Permittivity	8	2.3	2.3
3	Softening Temperature (°C)	120	105	160
4	Rating Temperature (°C)	60	75	105
5	Oil Resistance	Good	Good	Excellent

presents the electrical and physical characteristics of each type of pipe. Following the procedure described in Section 3, the experiments were repeated under each condition. The results of each experiment were measured using various instruments, recorded, and then analyzed to compare the outcomes across different conditions. The analysis focused on observing changes in charging voltage, discharge current, and electric charge over time, with particular attention to how these values varied when specific conditions were altered. This approach allowed us to identify trends and relationships, highlighting the influence of different experimental parameters on the electrostatic behavior.

The experimental results, shown in

Table 5. Electrostatic charging characteristics measurement graph.

RESULT 1
RESULT 2
RESULT 3
RESULT 4
RESULT 5
RESULT 6
RESULT 7
RESULT 8
RESULT 9

, indicate that electrostatic charging voltage increases when the pump is started, but this upward trend diminishes once the pump is stopped, although charging voltage may still fluctuate. The discharging current increases upon grounding, then decreases and stabilizes once the pump is stopped. Additionally, the amount of electrostatic charge shows a decreasing trend from 60 to 90 s after the initial measurement and stabilizes at a constant value after 90 s. Voltage measurements taken at different points along the pipeline, from inlet to outlet, show the highest reading at CH1 near the inlet, while at CH4, the value approaches zero. This decline is attributed to the discharge of electrostatic from the flammable liquid through grounding, or through the grounding connection installed between CH3 and CH4 to measure the discharge current.

Table 5 compare the results for charging voltage, discharging current, and electric charge amount across various cases.

RESULT 1–RESULT 3 indicate that increasing transferring pressure correlates with higher charging voltage, greater discharging current, and a larger steady-state electric charge amount. RESULT 2 highlights that after grounding, variations in discharge current are observed only during the first 30 s of pump operation. Beyond this, the discharge current stabilizes, and once the pump stops, the system enters a steady state, producing a constant discharge current. RESULT 4 compares the voltage across different pipe materials, showing that PVC exhibits a higher charing voltage than PP. Under high-pressure conditions, similar trends were observed across all three materials (PP, PE, and PVC). We have not included the corresponding graphs, as they do not provide additional insight. RESULT 5 and RESULT 6 analyze the effect of liquid temperature on charging voltage at high pressure (0.12 bar) for 16 A pipes. The results show that as the temperature rises, the charging voltage decreases in PVC pipes but tends to increase in PP pipes, with PE pipes displaying a trend similar to PVC. The reasons behind these differences are discussed in detail in Section 4.3, where we explore the material-specific interactions and thermal properties that influence the electrostatic behavior under varying temperature conditions. RESULT 7 compares charging voltage measurements by diameter in PP pipes, indicating that larger diameters (20 A and 25 A) have lower charging voltages than smaller ones (16 A). RESULT 7 compares charging voltage measurements by diameter in PP pipes, indicating that larger diameters (20 A and 25 A) have lower charging voltages than smaller ones (16 A). While in Case 23, CH1 and CH2 show a decrease in charging voltage with an increase in pipe diameter, and CH3 shows an unexpected increase in charging voltage despite having the same diameter as CH2. This can be explained by the fact that in Case 23, the pipe diameter decreases from 20 A in CH2 to 16 A in CH3, leading to increased turbulence and friction, which in turn raises the charging voltage. In RESULT 8, the effect of PVC pipe length is examined, showing that charging voltage increases with pipe length. This can be interpreted as shorter pipes result in a decrease in the total charge generated, which leads to a smaller increase in charge density compared to longer pipes. Conversely, RESULT 9 reveals an unexpected trend in PP pipes: shorter pipes exhibit higher charging voltages than longer ones, contrary to the initial hypothesis. The reason for this is also discussed in Section 4.3.

4.3. Experimental Hypothesis Validation

4.3.1. Flow Rate for Flammable Liquids

In the correlation analysis between flow rate and charging voltage of the flammable liquid, the experimental results align with the hypothesis, demonstrating that charging voltage increases as flow rate increases, when other variables remain constant.

4.3.2. Temperature of Flammable Liquids

The correlation analysis between temperature and charging voltage of the flammable liquid revealed some inconsistencies with the experimental hypothesis. As the temperature increased, the charing voltage for PP pipes also increased, which is consistent with the hypothesis. However, for PVC and PE pipes, charging voltage decreased with increasing temperature. This outcome for PVC and PE pipes is challenging to interpret solely based on the hypothesis that increasing temperature decreases the conductivity of flammable liquids. Alternative interpretations for these results are discussed below.

In [8], the authors proposed an approach to explain the charging phenomenon observed when oil flows along the surface of an insulator, attributing it to differences in work function between the liquid and solid materials. Their findings indicate that streaming electrification in oil leads to a positive charge, suggesting that non-polar polymers like PP and PE (used in our study) have a higher work function than the oil. The work function of the materials used in the pipes (PP, PVC, PE) decreases. Specifically, when the pipe temperature rises due to the heated flammable liquid, the potential barrier of the pipe material is lowered, reducing the work function and facilitating electron movement [19,20,21,22]. Overall, an increase in temperature reduces the work function difference between the flammable liquid and the piping materials, potentially resulting in a decrease in electrostatic charging voltage.

For PP pipes, the results differ from those observed with PVC and PE. PP pipes have a softening temperature of 160 °C and a rated temperature of 105 °C, so even with an increase in the temperature of the flammable liquid, the work function does not significantly decrease. This is because PP pipes have better temperature resistance than PVC and PE, meaning their potential barrier does not reduce as easily. Consequently, in PVC and PE pipes, the work function decreases with the rising liquid temperature, leading to a reduction in charging voltage. In contrast, for PP pipes, the decrease in work function is likely smaller. This suggests that the reduced conductivity of the flammable liquid has a comparatively larger impact, causing an increase in charging voltage with rising temperature, as hypothesized.

Another possible way to interpret the differing results for PVC, PE, and PP pipes is through the triboelectric factor. Eui-Cheol Shin et al. introduced an electrostatic sequence based on a triboelectric factor formula [23], which incorporates physical variables such as the Seebeck coefficient, density, specific heat, and thermal conductivity. Meanwhile, the PVC and PE materials used as pipes in the experiment exhibit negative polarity, while the PP material exhibits positive polarity. Since diesel, the flammable liquid used in the study, is a non-polar substance, the polarity of the charge can vary depending on factors such as the type and condition of the contact material [24].

4.3.3. Material of Pipe for Flammable Liquids

In the correlation analysis between the pipe material and the electrostatic voltage of the flammable liquid, the electrostatic charging voltage was highest in PVC piping, followed by PE and PP. This result aligns with the hypothesis that PVC piping, with a higher dielectric constant than PE and PP, would produce a higher charging voltage. Dielectric constant, or permittivity, reflects the material’s ability to allow electrical displacement under an electric field, indicating how well the electric field generated by flowing flammable liquids is transmitted through the piping. This also corresponds to the material’s capacity to store electrical energy within the electric field. Thus, PVC piping shows the highest charging voltage because its dielectric constant is about 3.5 times greater than that of PE and PP, and its lower volume resistivity allows the charge on the flammable liquid’s surface to induce electrostatic charge more readily on the pipe surface.

4.3.4. Diameter of Pipe for Flammable Liquids

The experimental results align with the hypothesis that a smaller pipe diameter increases the charging voltage due to greater friction caused by higher pressure. In RESULT 7, the high charging voltage observed at CH1 (25 A) with the largest pipe diameter in Case 23 can be attributed to the initial high pressure. As the flow rate increases, the flow transitions from laminar to turbulent. This transition is governed by the Reynolds number, a dimensionless parameter directly proportional to the pipe diameter and flow velocity. The higher Reynolds number associated with turbulence enhances charge separation and accumulation, leading to the observed high voltage at CH1 (25 A). Specifically, when the flammable liquid flows from the 16A inlet pipe and valve into the 25 A pipe, the increase in Reynolds number promotes turbulence, further contributing to the elevated voltage.

4.3.5. Length of Pipe for Flammable Liquids

The correlation analysis between pipe length and charging voltage supports the hypothesis that voltage increases with pipe length. However, variations in voltage trends—whether increasing or decreasing—depend on experimental conditions such as pipe material, diameter, length, and liquid temperature. In RESULT 9, a high voltage was observed in Case 7, which uses a shorter PP pipe (0.61 m) than Case 1. This result can be explained by the relatively minor difference in pipe length between these cases compared to other influencing factors. Additionally, the increased frictional force caused by turbulence generated by the multi-stage diameter piping in Case 7 may have contributed to the high voltage.

5. Conclusions

In this study, an experimental apparatus was constructed considering the flow conditions of diesel oil, a flammable liquid, and the electrostatic charge characteristics were observed and analyzed. The main results are as follows:

• The electrostatic charging voltage tended to increase as the liquid movement speed (pressure, flow rate) increased. This can be explained by the increased frequency of frictional contact and the increased amount of charge accumulation, which is consistent with previous studies.
• As the temperature of the liquid increased, the charging voltage decreased in PVC and PE pipes, while the charging voltage increased in PP pipes. Different materials showed different trends, which means that both the conductivity reduction effect of flammable liquids and the work function change of solid materials should be considered when the temperature changes to obtain accurate electrostatic charge characteristics. It is important to note that an increase in temperature does not necessarily mean an increase in electrostatic hazard; on the contrary, a lower temperature may actually result in a higher electrostatic voltage under certain conditions.
• In the comparison of transferring pipes by material, PVC pipes have the highest electrostatic charging voltage, followed by PE and PP pipes. This can be interpreted through the dielectric constant of the pipe material. In the comparison of the diameter and length of the pipe, the charging voltage increased as the diameter decreased and as the length increased. In some cases, the large pipe diameters resulted in higher voltages, which may be a result of turbulent flow conditions.

The experimental apparatus configuration, methods, and procedures proposed in this paper are designed to provide quantitative data to identify electrostatic discharging as a potential ignition source in fire and explosion hazardous areas. In particular, the experimental apparatus can measure electrostatic charging voltage and charge amount, serving as an effective means to objectively evaluate and manage electrostatic occurrences in practical industrial sites. In addition, the experimental results derived from this study can be used as specific and reliable data for controlling and managing electrostatic to a safe level, and it is expected that they can be used as a basis for more clearly identifying the hazards of electrostatic in industrial safety management.