Domestic Large-caliber Longitudinal Welded Pipe Production Process Introduction
- Apr 13, 2018 -

Domestic Large-caliber Longitudinal Welded Pipe Production Process Introduction

Straight seam welded pipes are formed by bending steel plates or strips and then welded. Divided into straight seam welded pipe and spiral welded pipe. According to the purpose, it can be divided into general welded pipe, galvanized welded pipe, oxygen welded pipe, wire bushing, metric welded pipe, idler pipe, deep well pump pipe, automotive pipe, transformer pipe, welded thin-walled pipe, welded special-shaped pipe and spiral welded pipe.

First, the main production process description of large-diameter straight seam welded pipe:

1. Prospecting: After the steel plate used to make large-diameter submerged-arc welded straight-joint steel pipes enters the production line, full-plate ultrasonic inspection is first performed;

2. Milling: Double-sided milling of the two edges of the steel plate by a milling machine to achieve the required plate width, plate edge parallelism and groove shape;

3. Pre-crimping: Pre-bending machine is used to pre-bend the edge so that the edge of the board has a curvature that meets the requirements;

4. Forming: In the JCO molding machine, first half of the pre-bent steel plate is punched several times and pressed into a "J" shape. Then, the other half of the steel plate is also bent and pressed into a "C" shape, finally forming an opening. The "O" shape

5. Pre-welding: seaming the formed straight welded steel pipe and using gas shielded welding (MAG) for continuous welding;

6. Internal welding: Use vertical multi-wire submerged arc welding (up to four wires) to weld inside the straight seam steel pipe;

7. Outer welding: use vertical multi-wire submerged arc welding to weld outside LSAW steel pipe;

8. Ultrasonic inspection I: 100% inspection of the internal and external welds of the longitudinal welded steel pipe and the base metal on both sides of the weld;

9. X-ray inspection I: Conduct 100% X-ray industrial television inspection of internal and external welds, using image processing systems to ensure the sensitivity of the inspection;

10. Expanded diameter: Expand the length of the submerged arc straight seam steel pipe to increase the dimensional accuracy of the steel pipe, and improve the distribution of the internal stress of the steel pipe;

11. Hydraulic pressure test: The root diameter of the expanded steel pipe is tested on the hydrostatic testing machine to ensure that the pipe meets the required test pressure. The machine has automatic recording and storage functions;

12. Chamfering: the pipe after passing the inspection is processed at the pipe end to meet the required pipe end groove size;

13. Ultrasonic inspection II: Ultrasonic inspections were performed one by one to check for possible flaws in straight seam welded steel pipes after diameter expansion and water pressure.

14. X-ray examination II: X-ray industrial television inspection and tube-end weld seam examination of steel tubes after diameter expansion and hydrostatic pressure testing;

15. Tube end magnetic particle inspection: This inspection is performed to find the tube end defects;

16. Anti-corrosion and coating: The qualified steel pipe is anti-corrosion and coating according to the user's requirements.

Second, large-diameter thick-wall welded pipe dry welding technology analytical explanation:

Automatic welding of large-diameter, thick-walled (above 21mm) pipelines often use U-grooves or compound-type bevels, due to U-grooves, composite groove processing time-consuming, labor-intensive control of pipe welding efficiency. V-shaped groove processing is simple, save time and effort, but when large-diameter, thick-walled pipeline V-type groove automatic welding, such as improper selection of welding process parameters will lead to welding defects.

The welding method uses STT root welding + CRC-P260 automatic welding machine heat welding, filling, capping. Welding equipment: Lincoln STT welder, Lincoln DC-400, CRC-P260 automatic welder. Protective gas: 100% CO2 for STT root shield gas, 80% Ar+20% CO2 for fully automatic welding shield gas.

Automatic welding is often used for compound or U-grooves. V-grooves can also be used for small-walled pipelines. Their common feature is that the gap at the top of the groove is small. The wall thickness of the second line of the West-East Gas Pipeline is 21.0mm, and the width of the upper mouth of the V-shaped groove is approximately 22mm, which is close to the limit of the CRC-P260 torch swing. This kind of groove pattern is a huge challenge for automatic welding. Based on past experience, automatic welding test welding process parameters were determined.

The above parameters were used for the automatic welding test. Automatic welding joints were found to be prone to defects such as non-fused layers, unfused sidewalls, dense pores, and over-height at the overhead welding position.

In order to ensure a good cover forming effect, the cover welding in the selection of smaller

While reducing welding torch oscillation frequency as much as possible, the cover weld is thin and wide, which reduces the time of molten pool existence and achieves the purpose of reducing the overhead height of the overhead welding position. According to the welding results and analysis, the STT root welding + CRC automatic welding filling and capping process parameters of the second line of the West-East Gas Pipeline were determined. According to the welding parameters in Table 3, the welds have no defects such as blowholes, cracks, and no welds, and the surface of the weld seam is formed. The macroscopic metallographic phase is good.

The mechanical properties of the welds were tested by the Welding Technology Center of the China Petroleum Pipeline Science Research Institute. All the indicators were in line with the construction requirements of the second line of the West-East Gas Pipeline. The successful application of STT root welding + CRC-P260 automatic welding on large-diameter, thick-walled (V-groove) pipelines fully reflects the characteristics of high-quality, high-efficiency and low labor intensity of automatic welding technology.

Third, the straight seam welded pipe technical requirements and quality inspection:

According to GB3092 "Standard for Welded Steel Pipes for Low-Pressure Fluid Conveying", the nominal diameter of the welded pipe is 6~150mm, the nominal wall thickness is 2.0~6.0mm, and the length of the welded pipe is usually 4~10 meters, which can be length or length Factory. The surface quality of the steel pipe should be smooth, and there must be no defects such as folding, cracks, delamination, and lap welding. The surface of the steel pipe is allowed to have minor defects such as scribes, scratches, misalignment of welds, burns and scars that do not exceed the negative wall thickness deviation. Permissible thickening at the weld seam and presence of weld seams in the inner seam. Welded steel pipes should be tested for mechanical properties, flattening tests, and flaring tests, and must meet the requirements of the standard.

The steel pipe should be able to withstand a certain internal pressure. If necessary, a pressure test of 2.5Mpa shall be carried out to keep it from leaking for one minute. Allows eddy current testing instead of hydrostatic testing. Eddy current testing according to GB7735 "steel pipe eddy current inspection method" standard implementation. The eddy current testing method is to fix the probe on the frame, and the flaw detection and weld are kept at a distance of 3~5mm. The weld is scanned by the rapid movement of the steel pipe. The flaw detection signal is automatically processed and automatically sorted by the eddy current flaw detector. To achieve the purpose of detection. After the flaw detection, the welded pipe was cut off by a flying saw at a specified length and turned off the line. Both ends of the steel pipe shall be chamfered flatly and printed. The finished product shall be packed in a hexagonal shape and then shipped from the factory.