Welding method and welding material consumption calculation of oil and gas long-distance pipeline

This paper briefly summarizes the welding and installation methods of oil and gas long-distance pipeline, analyzes the characteristics of welding materials used in different welding processes, modifies the theoretical formula of welding material consumption, obtains the final correction formula, and calculates various welding material consumption of different welding processes for guiding construction.

Introduction

The long-distance oil and gas pipeline laying has the characteristics of long route, large span, wide range and complex landform. The natural conditions at the construction site also change from time to time. Therefore, the welding methods of long-distance pipeline vary with the differences of site environment.
At present, with the improvement of the performance of pipeline steel, the continuous progress of welding materials and welding technology, and the change of pipeline welding process, many kinds of welding processes have been developed, mainly including manual welding rod up welding, manual welding rod down welding, self shielded flux cored wire semi-automatic welding, consumable gas shielded welding, pipeline all position automatic welding, etc. In the construction of long-distance pipeline in China, the most commonly used are downward welding, semi-automatic welding and gas shielded welding. These welding processes can cooperate with advanced equipment to realize mechanized flow operation in the construction of long-distance oil and gas pipeline.
These welding processes have their own characteristics. The manual welding equipment is simple, easy to enter the site and occupies less land during construction. It is suitable for local difficult sections (such as mountainous areas where the equipment is difficult to reach) and dead joints and repair welding. Downward welding and semi-automatic welding process require less equipment, small equipment volume, low failure rate and flexibility. This method has uniform and reliable welding quality and fast speed. It has developed and popularized rapidly in pipeline construction. At present, it has become the main method of large-scale pipeline welding in China. The full-automatic welding process has high efficiency and high welding qualification rate, which can reduce the labor intensity of welders, but the full-automatic welding equipment is heavy and expensive, so it is not suitable for relocation. The full-automatic welding process is applicable to the construction of large-diameter pipelines and pipelines in plain areas with less crossing and connection. It is difficult to give full play to its advantages in mountainous areas and areas with complex terrain.

Calculation of welding material consumption

The parameters related to the cross-sectional area of welded junction shall be determined according to the specific size of pipe groove. In order to facilitate the calculation, take the safety reconstruction project of railway Dalian line (Anshan Dalian section) and China Myanmar natural gas pipeline project (domestic section) as examples respectively, and the relevant parameters are determined according to the requirements of the welding process specification and pipe contract documents of the project.

Electrode arc welding

Combined welding is often used in electrode arc welding. Different models or brands of electrodes will be selected according to the material, operating pressure and medium composition of the pipeline. In order to ensure the accuracy of calculation, the amount of electrodes for different passes in the same weld shall be calculated separately, so that the required amount of electrodes of different models or brands can be accurately mastered. In oil and gas pipeline welding, electrodes are classified according to coating types, mainly cellulose type, low hydrogen sodium type and low hydrogen potassium type. Most of them are non-iron powder electrodes, and the theoretical calculation formula of consumption quota is [1]:

  • G=ALρ(1+Kb)/(106Kn)G=ALρ(1+Kb)/(106Kn) (1)

Iron powder low hydrogen electrode is used for a few pipeline welding, and its calculation formula is:

  • G=ALρ/(1−Ks)/106G=ALρ/(1−Ks)/106 (2)

In the formula:

  • G – electrode consumption, kg; A – sectional area of weld deposited metal, mm2; L – weld length, mm;
  • ρ—— Electrode metal density, 7.85g/cm3; KB — quality coefficient of drug skin, taking 25% ~ 40%;
  • Kn – conversion coefficient of metal from electrode to weld, including combustion and splash loss of 5% ~ 10%, and unused electrode head loss of 10% ~ 15%, so the conversion coefficient is 0.75 ~ 0.85.
  • KS – loss coefficient of welding rod, taken as 0.33 ~ 0.6.

Taking non-ferrous powder electrode arc welding as an example, the consumption of electrode is related to coating quality coefficient, conversion coefficient and weld area. The KB and kn values of different grades of welding rods are different, and the specific values can be queried according to the relevant data provided by the manufacturer. The calculation of welding material consumption for electrode arc welding takes the line welding of Tieda line safety reconstruction project (Anshan Dalian section) as an example, the root welding is cellulose electrode (E6010, awsa5.1), the value is KB = 0.40, kn = 0.77 [1], and the hot welding, filling and covering are low hydrogen electrode (E5515-G, GB / T5518), the value is KB = 0.32, kn = 0.80 [1]. Electrode diameter Φ 3.2/4.0mm.
As the oil and gas pipeline is mainly welded with circumferential butt welds, its welding positions (see Figure 1 below) include flat welding (approximately 11-1 points), vertical welding (approximately 1-5 points and 7-11 points) and overhead welding (approximately 5-7 points). The electrode consumption per unit length of each welding position is different. In the vertical welding position, the electrode consumption increases by 10% compared with that in the flat welding position, and in the overhead welding position, the electrode consumption increases by 20% compared with that in the flat welding position [2]. During construction, there are also electrode losses, such as the loss of electrode during transportation and storage, insufficient utilization of electrode during welding (abandoned due to large amount of electrode remaining), a small amount of electrode coating can not be used due to cracks, bubbles, impurities, falling off and rupture, and abandonment of electrode caused by other reasons (such as bending, excessive eccentricity, arc striking failure, etc.), Therefore, the consumption of welding rod shall be calculated according to the coefficient of 1.2.
Therefore, the amount of welding rod used in manual arc welding can be corrected as follows:

  • G=ALρ(1+Kb)/(106Kn)×1.1×1.2G=ALρ(1+Kb)/(106Kn)×1.1×1.2 (3)

The consumption of a single welded junction is:

  • G=πDAρ(1+Kb)/(106Kn)×1.1×1.2G=πDAρ(1+Kb)/(106Kn)×1.1×1.2 (4)

In the formula: G – amount of welding rod for single welding junction, kg; D – pipe diameter, mm.

According to formula (3) and relevant parameter values, the consumption of single electrode when manual arc welding is adopted for the line of Tieda line safety reconstruction project (Anshan Dalian section) can be calculated. The calculated values are shown in Table 1 below.

20211103082437 44220 - Welding method and welding material consumption calculation of oil and gas long-distance pipeline

Figure 1. Diagram of welding position schematic

Table 1. Calculation of welding materials consumption in Tie Da safety reformation project (Anshan-Dalian)

Pipe diameter

(mm)

Wall thickness

(mm)

Butt clearance

(mm)

Blunt edge

(mm)

Calculated dosage (kg / mouth)

Calculated dosage (kg / mouth)

Electrode arc welding

Consumption of cellulose electrode (root welding)

Consumption of low hydrogen electrode (hot welding + capping)

813

11.0

2.7

1.5

0.43

3.41

813

12.5

2.7

1.5

0.43

4.29

Electrode arc root welding + flux cored wire semi-automatic welding

Consumption of cellulose electrode (root welding) kg / mouth

Flux cored wire (filling, capping)

813

11.0

2.7

1.5

0.43

2.34

813

12.5

2.7

1.5

0.43

2.90

The main welding processes of the main line are: cellulose electrode root welding + self-protection flux cored wire semi-automatic welding and capping, cellulose electrode root welding + low hydrogen electrode capping. The blunt edge height P is 1 ~ 2 mm, with an average of 1.5 mm; Groove angle α For 44 ˚; The average weld reinforcement h is 2 mm; The root butt clearance B is 1.0 ~ 3.5 mm, with an average of 2.7 mm; Weld width C (mean value) and number of weld passes: 12.93 mm for 11 mm wall thickness, 4 layers of weld passes, including 1 filling layer m (excluding hot welding layer), 14.14 mm for 12.5 mm wall thickness, 5 layers of weld passes, including 2 filling layers m (excluding hot welding layer); Root weld layer thickness δ 1: 3.0 mm, thickness of thermal welding layer δ 2. Take 2.5 mm; The specification of welding rod is E6010( Φ 3.2/ Φ 4.0 mm), the specification of self protective flux cored wire is e71t8-ni1j( Φ 2.0 mm), and the grinding thickness of each layer of electrode arc welding is 0.4 mm.

Semi automatic welding with self shielded flux cored wire

The semi-automatic welding process of self shielded flux cored wire is generally combined with other root welding processes, and the root welding adopts electrode arc welding or STT welding. The quota calculation formula of self protective flux cored wire is shown in formula (4).

  • G=ALρ/(1000Kn)G=ALρ/(1000Kn) (5)

In the formula: kn – conversion coefficient of metal from welding wire to weld, including loss of burning loss and splash, and the flux cored wire kn is taken as 0.72 ~ 0.75.
The unit consumption of welding wire is also different at different welding positions. For all position welding of pipeline, the consumption of welding wire is the same as that of welding rod, which can be multiplied by a 1.1 coefficient; In case of insufficient utilization and loss of welding wire during construction, it can be multiplied by 1.05 coefficient, and the theoretical formula of welding wire consumption can be corrected as follows:

  • G=3.14DAρ/(1000Kn)×1.10×1.05G=3.14DAρ/(1000Kn)×1.10×1.05 (6)

Using manual arc welding + flux cored wire semi-automatic welding process, the line of Tieda line safety reconstruction project (Anshan Dalian section) can be calculated( Φ 813) when flux cored wire is used for semi-automatic welding of pipeline, the consumption of single welding material is shown in Table 2.
STT root welding + flux cored wire semi-automatic welding process is adopted, and the calculation of root welding wire is the same as formula (6); The calculation of flux cored wire for filling and covering is the same as formula (6), in which the conversion coefficient kN of solid wire for gas shielded welding is 0.9 ~ 0.95, which can calculate the consumption of single welding material when STT root welding + flux cored wire semi-automatic welding is adopted for the line of China Myanmar natural gas pipeline project (domestic section), as shown in Table 2 below.

Table 2. Calculation of welding materials consumption in Myanmar-China oil & gas pipeline project

Pipe diameter

(mm)

Wall thickness

(mm)

Butt clearance

(mm)

Blunt edge

(mm)

Solid welding wire for gas shielded welding (root welding) kg / mouth

Flux cored wire (filler) kg / mouth

Flux cored wire (cover) kg / mouth

ER70S-G

E81T8-Ni2J

E551T8-K2

1016

12.8

3.0

1.0

0.28

3.45

0.74

1016

15.3

3.0

1.0

0.27

4.63

0.88

The specification of main pipeline is Φ one thousand and sixteen ×  12.8 mm, Φ one thousand and sixteen ×  15.3 mm; The blunt edge height P is 0.6 ~ 1.4 mm, with an average of 1.0 mm; Groove angle α For 44 ˚; The average weld reinforcement h is 2 mm; The root butt clearance B is 2.5 ~ 3.5 mm, with an average of 3.0 mm; Weld width C (mean): 15.04 mm for 12.8 mm wall thickness and 17.06 mm for 15.3 mm wall thickness; Root weld layer thickness δ 1:2.5 mm.

Automatic welding

The full-automatic welding adopts gas shielded solid welding wire for welding, and the root welding and filling cover welding adopt welding wires of different models and specifications, which shall be calculated separately.
Because the calculation of the above formula is very complex, in order to improve efficiency and ensure the accuracy of calculation, the automatic calculation function in Excel can be used to compile and set relevant formulas, and automatically generate results after entering parameters, so as to obtain the required values. Based on specification Φ eight hundred and thirteen × The calculation of process consumption of cellulose electrode root welding + flux cored wire semi-automatic welding and capping for 11mm pipeline is taken as an example, as shown in Table 3 below.

Table 3. Calculate welding materials consumption with Excel table formula

Kn Conversion coefficient of metal from welding wire to weld (burning loss, splash and unused welding wire loss) 0.72~0.75 0.75 Kb Weight coefficient of flux cored wire powder 0.15~0.2 0.15
Kn Conversion coefficient of cellulose electrode (burning loss, splash and unused electrode head loss) 0.53 Kb Weight coefficient of cellulose electrode coating 0.4 Wall thickness 11.0 Wall thickness 12.5
Number of welded junctions Number of welded junctions
A1 Sectional area of deposited metal of root weld 9.01 3017 1836
A3 Sectional area of deposited metal of semi-automatic flux cored wire filling and cover weld 75.82 Cellulose 1900.16
Electrode consumption
G root Theoretical value of cellulose (root welding) electrode consumption (single port volume / total volume) 0.48 1439.52 Amount of cellulose electrode 1900.76
G filling Theoretical value of filler and cover welding wire consumption (single mouth / total amount) 2.33 7032.72 Flux cored wire consumption 7890.71
G root solid Actual value of cellulose (root welding) electrode consumption (single port volume / total volume) 0.63 1900.76
G stem Actual value of flux cored wire consumption (single flux / total flux) 2.62 7890.71

Analysis of calculation results

Taking the line of the first bid section of the railway Dalian line safety reconstruction project (Anshan Dalian section) as an example, the main line and joint welding have been completed, and cellulose electrode root welding + self-protection flux cored semi-automatic welding filling cover are adopted. According to the data provided by the welding material requisition and consumption details of the EPC project department, the consumption coefficients of cellulose electrode and flux cored wire are 0.69kg/well and 2.47kg/well respectively; There are 3017 pipe junctions with wall thickness of 11mm and 1836 pipe junctions with wall thickness of 12.5mm. According to the calculation data in Table 2 above, the calculated consumption of single port cellulose electrode and flux cored wire is 0.43kg/well and 2.55kg/well respectively. Comparing the calculated and actual values of welding material consumption, the calculated value of root welding (cellulose) electrode consumption is small, which deviates greatly from the actual consumption, and the calculated value of flux cored wire consumption is basically consistent with the actual value. Compared with the current quota [3], the calculated consumption of semi-automatic root welding rod and flux cored wire is slightly less than the quota consumption; The actual amount of root welding rod is slightly greater than the quota amount, and the actual amount of flux cored wire is slightly less than the quota amount. Therefore, it can be analyzed and judged that the cellulose electrode in this bid section has low use efficiency, underutilization and more loss and waste in on-site construction.

Conclusion

Long distance pipeline welding is a long-term dynamic process. There are many uncertain factors in determining the amount of welding materials, such as different proficiency and personal habits of welders, inconsistent butt clearance of each weld, different grooves of different batches of pipes, deviation between actual wall thickness and nominal wall thickness of pipes, changes in construction site environment and site, and commissioning of welding equipment, The quality, performance and parameters (such as electrode coating coefficient and conversion coefficient) of welding materials of the same model and different brands are different, and the loss of welding materials in the process of transportation, storage and requisition is different. Therefore, the results calculated by the above formula will deviate from the actual value, but the calculation results can provide reference for other projects. In different projects, the relevant parameters are corrected according to the actual situation to reduce the deviation between the calculated value and the actual value as much as possible and improve the accuracy. In this way, the above calculation method can accurately guide the construction, determine the consumption quota and avoid waste caused by excessive welding materials, And lead to inventory backlog, increasing storage costs; It can also avoid that the shortage of welding materials will affect the procurement and construction progress, and lead to secondary additional transportation costs. In particular, international projects have the characteristics of long distance, high transportation costs and long material customs clearance time, so the accuracy of welding material consumption calculation is more important.
Author: Li Dan

Source: Network Arrangement – China Welded Pipe Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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Reference:

  • [1] Xu Xiaobing. Construction technical manual of oil and gas long distance pipeline engineering [M]. Beijing: Petroleum Industry Press, 2011:27-29
  • [2] Zaitsev, long distance pipeline welding and installation engineering manual [M]. Translated by Li Rongen. Beijing: Petroleum Industry Press, 1991:53
  • [3] Wang Qinmin, Meng Qingfeng, Zhang Xuefeng, et al. Budget quota of petroleum construction and installation engineering (Volume IX) long distance transmission pipeline engineering [M]. Beijing: Petroleum Industry Press, 2014:197-199
  • [4] Li Dan. Welding method and welding material consumption calculation of oil and gas long-distance pipeline [J]. Journal of petroleum and natural gas, 2021, 43 (3): 267-272 https://doi.org/10.12677/JOGT.2021.433060

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