Project Overview

In order to further improve the upstream and downstream industrial chain of its energy sector, promote industrial restructuring and transformation, and enhance its industrial status, China National Chemical Corporation invested in the construction of a 1 million t/a ethylene and refinery expansion project based on the already completed and operational Sinochem 12 million t/a refinery project. The project is located in the southern bank of Meizhou Bay, Huian County, Quanzhou City, within the Quanzhou Huian Petrochemical Park. The steel structure of the plant-wide chemical process and thermal pipeline corridor maps 1, 2, 3, 5, and 8 is installed by China Petroleum & Chemical Engineering Corporation No. 6 Construction Company (hereinafter referred to as "the Sixth Construction Company"), totaling 22,000 tons of steel structure.

The steel structure is prefabricated by the manufacturer and delivered to the site, with the project department responsible for on-site installation using high-strength bolted connections. This project has a long front (6.5 km), large volume, and short construction period (3 months).

 

 

Comparison of Preparation Time for High-Altitude Work Platforms and Scaffolding

From the beginning of the project, it has faced the problems of huge workload and tight deadlines. How to complete more than 20,000 tons of steel structure within the stipulated 3-month construction period has become a major challenge for all project executors. The choice of measures to ensure construction will determine the success or failure of the project implementation.

According to the scale of the project, the project department divided the entire steel structure construction into 10 sections, with an average of 2,200 tons of steel structure per section. According to the schedule requirements, 24 tons of steel structure need to be completed daily.

Using Scaffolding

Considering the usual practice of ensuring construction operation platforms in installation projects, scaffolding is generally used to ensure construction. This construction method is technically mature and has high safety. The scaffolding for the pipeline steel structure is generally constructed using "column-hugging scaffolding" to ensure sufficient operating platforms when installing beams.

Calculation of Scaffolding Usage for Steel Columns Using Column-Hugging Scaffolding:

(1) 10 2m horizontal bars are needed for every 1m of scaffolding;

(2) For columns (6m < h < 12m), 8 vertical bars are needed for each column;

(12m < h < 24m), 16 vertical bars are needed for each column;

(3) 2 cross-couplers are needed for each 2m horizontal bar;

(4) 1 coupler is needed for every two vertical bars;

(5) 4 diagonal bars are needed to reinforce each column, and 4 rotary couplers are needed for each diagonal bar;

(6) Two operating platforms are needed for 12m and below, with 8 jump rows per platform;

(7) Four operating platforms are needed for above 12m and below 20m, with 8 jump rows per platform. A total of 598,168m of scaffolding poles, 504,344 couplers, and 192 jump rows are needed. The planned amount of scaffolding and components is 3245.35t. Detailed calculation of scaffolding usage is shown in the table below:

 

 

Using Aerial Work Platforms

Aerial work platforms are special vehicles used to transport personnel and equipment to the site and perform aerial work. They are widely used in high-altitude work in the fields of electricity, streetlights, municipal engineering, and advertising. They are rarely used in the construction and installation of petrochemical projects, and even if used, they are only limited to the repainting of the outer walls of tanks, repair of streetlights, and other sporadic high-altitude work after installation.

　　According to the project department's plan, two work teams need to be arranged for each section on average, each team needs to be equipped with two 25t truck cranes, and each crane needs to be equipped with two 26m aerial work platforms to complete the installation of beams. Considering the phased concentrated delivery, it is estimated that six sections will need to add one more work team, increasing one 25t truck crane and two aerial work platforms. Overall, an average of 2 x 2 x 10 + 6 x 2 = 52 aerial work platforms are needed to complete the construction in 3 months.

　　After market research, there are abundant resources of aerial work platforms in the local area and its surroundings, including 3 rental companies in Shanghai with a long-term inventory of 50 units. Moreover, it only takes 1 day to dispatch to the construction site, and 2 days for vehicle entry inspection. Therefore, aerial work platforms are more secure in terms of both resources and time.

　　Note: ① There are 14m, 18m, 20m, and 26m aerial work platforms available. The 26m platform has better versatility.

Comparison of Preparation Time for Aerial Work Platforms and Scaffolding. Using scaffolding for construction will also have the following problems:

　　(1) If considering procurement:

　　Scaffolding poles belong to Class A materials of CNPC, with a minimum procurement cycle of 45 days and a minimum of 7 days to meet the usage conditions after inspection.

　　(2) If considering nationwide transportation:

　　It needs to be gradually dispatched from Xinjiang, Northeast China, East China, Sichuan, etc., with a transportation distance of over 1000km, and the transportation and dispatch time cannot be controlled.

　　(3) If considering using aerial work platforms:

It takes 1 day for entry and 2 days to meet the usage conditions after inspection.

　　The list is as follows:

 

 

Considering the contract schedule, if scaffolding is used, the project will fail before it even starts.

3. Cost Comparison Analysis of Aerial Work Platforms and Scaffolding

(1) Erection Cost

　　If column-hugging scaffolding is used for the installation of bolted steel structures in the pipeline corridor, column-hugging scaffolding must be erected for each column to meet the conditions for installing steel beams.

　　After counting the number of spans and axes of each pipeline corridor, the number of columns to be erected can be calculated. After counting the columns of the same height within a certain range, the erection perimeter and height can be calculated, and the total erection area can be calculated:

　　The total scaffolding construction cost is calculated as follows: the number of columns per drawing × the perimeter of the scaffolding (distance between the centerlines of two uprights) × the scaffolding height (from ground level to the operating platform) = scaffolding construction area. Multiplying this by the corresponding unit price gives the total scaffolding construction cost, which is 4,291,936.00 yuan.

　　See the table below for detailed calculations:

 

 

(2) Transportation Costs

　　By calculating the usage of uprights, couplers, and jump-outs, and multiplying by their respective weights (upright: 4.17 kg/m; cross coupler: 1 kg/piece; rotary coupler: 1.15 kg/piece; jump-out: 19 kg/piece), the total weight is calculated as 3001.49t. The transportation cost is 20,000 yuan/truck, with each truck carrying an average of 30t. A total of 100 truckloads are needed, costing a total of 2 million yuan.

　　See the table below for detailed calculations:

 

 

(3) Depreciation Costs 　　

The procurement price is calculated by multiplying the quantity of each specification of uprights, couplers, and jump-outs (see: Project Planning) by the corresponding unit price, resulting in 25,264,744.00 yuan. Considering a 3-year depreciation, and assuming the project takes 1 year, the depreciation cost is 25,264,744.00 / 3 = 8,421,581.33 (yuan).

　 　See the table below for detailed calculations:

 

 

(4) Total Scaffolding Construction Cost

　　Total scaffolding construction cost = Construction cost + Transportation cost + Depreciation cost = 4,291,936.00 + 2,000,000.00 + 8,421,581.33 = 14,713,517.33 (yuan)

2. High-Altitude Work Platform Cost Statistics

　　Calculated according to the quantity list in "Project Planning" as follows:

 

 

3. Comparison Analysis of Scaffolding Construction and High-Altitude Work Platform Costs

　　The cost difference between using scaffolding and a high-altitude work platform is: Scaffolding construction cost - High-altitude work platform cost = 4,291,936.00 - 3,630,711.72 = 661,224.28 (yuan)

　　The total cost difference is: Total scaffolding construction cost - High-altitude work platform cost = 14,713,517.33 - 3,630,711.72 = 11,082,805.61 (yuan)

Conclusion

　　In summary, for the installation of the gallery bolted steel structure, using a high-altitude work platform is more cost-effective and advantageous than using scaffolding, both in terms of time planning and cost.