Discussion on inspection of pipeline connections for oil and gas transportation at PetroChina – Chinese piping solutions provider

The process flow and most important test contents of pipe connections for oil and gas transmission are presented. The requirements of national standards and CNPC order conditions are analyzed for evaluating the pipe connection process, small batch trial production, first batch testing and group batch testing. Existing problems in testing pipe connections are summarized and sensible suggestions for testing pipe connections are made. It is recommended that the buyer consider the technical agreement of the pipe connections from the aspects of real and economic advantages, such as: B. The specifications, the type of steel, the acquisition volume, the production difficulties and the maturity of the product of pipe connections are formulated comprehensively and appropriate test points are selected.

As part of pipeline engineering, pipe fittings play a role in changing direction, connecting, maneuvering, sealing, controlling, supporting, etc. Pipe fittings are used for pipe connection. These include angle pieces, tee pieces, reducer S pipe caps, bends, pipe outlets flanges, blind flanges and S pipe nipple . In order to check the coordination between the new production process and the pipe fittings production line and the conformity between the new products and order requirements, and avoid the waste of resources caused by the unqualified batch of pipe fittings, During the production of pipe fittings, manufacturing process qualification, small batch trial production, first batch testing and batch testing are carried out. The requirements of relevant standards and technical agreements currently apply Inspection of pipe connections are inconsistent and not easy to implement. According to the production process of pipe fittings, the problems in testing pipe fittings for oil and gas transportation are discussed in detail and suggestions are made.

1. The production process of seamless pipe fittings are as follows : (seamless steel pipe) material testing → Fading → Forming → Coil head straightening → Heat treatment → Surface treatment → Final surface processing → Dimensional inspection → Non-destructive testing → Mechanical property testing → Marking → Packaging and storage → Product shipping.
2. The production process of welded joints for pipes are as follows: (steel plate or welded pipe) Metal material inspection → Fading → Coiled pipe welding → Forming → Coil head straightening → Heat treatment → Surface treatment → Face processing Final → Dimensional inspection → Non-destructive testing → Mechanical property testing → Marking → Packaging and storage → Product shipping.

This includes metal material testing, heat treatment, size testing, non-destructive testing and mechanical property testing to ensure the quality of pipe fittings. During the audit itself, special attention should be paid to key processes.

1. Material inspection: Check the mother tube or steel plate furnace number, tube number, appearance size, marking, specifications, quality assurance, physical and chemical re-inspection of factory results and compliance with the requirements of the technical agreement.
2. Discharge: Typically, pipe fittings have different shapes according to different types of raw materials, steel plate raw materials or steel pipes. According to the different shapes of raw materials, check the consistency of the steel pipe/plate discharge size with the drawing label.
3. Coil tube welding: Check the consistency of process parameters such as steel plate size, welding method, current, voltage, etc. with process documents.
4. Molding: According to the molding method selected for each type of pipe connection, check whether the heating temperature, heating time, number of molding operations, interval between heating and molding, etc. are suitable. during molding are consistent with process documents.
5. Lamination and rounding: Check compliance with process documents for rounding, rounding, appearance, etc.
6. Heat treatment: Check the compliance of heat treatment parameters such as heating temperature, holding temperature, heating speed, cooling speed, holding time and other parameters with the heat treatment process.
7. Surface sandblasting treatment: Check whether the outer surface meets the requirements of Sa2.5 after sandblasting.
8. Pipe end processing: Check the appearance and size of pipe fittings after processing and compliance with standard requirements.
9. Size check: Check appearance, wall thickness, outer diameter, chamfer size and other parameters for compliance with standard requirements.
10. Non-destructive testing: Non-destructive testing of pipe fittings includes magnetic particle/penetration testing (choose one of the two) and ultrasonic testing, checking compliance of flaw detection instruments, flaw detection methods, sensitivity, inspection parts, non-destructive reporting and processing documents.
11. Mechanical properties: Verify compliance of physical and chemical sampling and test results with standard requirements.
12. Labeling: Check logo content, logo format and compliance with standard requirements.
13. Packaging and storage: Check the packaging and storage environment.
14. Product shipping: Check the completeness and completeness of the factory information, and check the pipe connections for any shock during transportation, lifting and loading.

For pipe fittings, national standards generally apply: GB/T 12459-2017 “Type and parameters of butt-welded steel pipe fittings” and GB/T 13401-2017 “Technical specifications for butt-welded steel pipe fittings”. top". Both standards support the application of these two standards. When purchasing pipe fittings, China National Petroleum Corporation (CNPC for short) generally follows CDP-S-OGP-PL-010-2014-3 “Technical specification for pipe fittings with DN350 and below for oil and gas pipeline construction” and CDP -S -OGP-PL-011-2014-3 “Technical Specification for Pipe Fittings with DN400 and Higher for Oil and Gas Pipeline Construction” and selects the standards according to the specifications of the pipe fittings to be purchased. Currently, the procurement standard for pipe fittings is based on the above two types of standards, and now goes into more detail about the different requirements of national standards and CNPC technical specifications for testing pipe fittings.

2.1 Evaluation of the pipe connection process

(1) Technical data for PetroChina pipe fittings.

• Provisions 5.2.3.1 of PetroChina Technical Specification CDP-S-OGP-PL-011-2014-3: Before official production of DN400mm (nominal diameter 400mm) pipe fittings, the supplier shall carry out a pipe process assessment individual accessories according to provisions. Process evaluation can be done through small batch trial production, sampling and inspection prior to production of the first batch. Section 5.2.3.2 of the technical specification states that the supplier may not repeat a single trial production in small batches if it has proven delivery performance for products with equal or higher steel content and larger diameter, as well as impeccable process evaluation documents ​​within one year before signing the contract. However, the PetroChina technical specification CDP-S-OGP-PL-010-2014-3 stipulates that connections for pipes from DN350 mm (nominal diameter 350 mm) do not need to undergo process evaluation.
• Appendix A of Technical Specification CDP-S-OGP-PL-011-2014-3 requires: Butt welding of process evaluation connections shall be subjected to 100% ultrasonic testing + 100% X-ray testing; Longitudinal/transverse crack test of process evaluation fittings tube body base material by ultrasonic flaw detection; Surface testing of process evaluation fittings by magnetic particle or penetration testing and Surface inspection of pipe joints by location and direction of sampling requirements for tensile, impact, guided bending and Vickers hardness testing, metallographic testing.

(2) National standards for pipe fittings. National standards do not require process evaluation.
(3) Comparative analysis. Pipe fittings manufactured in accordance with national standards do not require process evaluation, but PetroChina technical specifications: DN400mm and above must comply with the production order of “process evaluation test → small batch test → test first batch”. A process evaluation test and a small batch test can be dispensed with carrying out the process evaluation test to verify the feasibility of the process, the small batch test and the first batch test. Feasibility, small series testing, and first batch testing are used to verify the feasibility of the mass production process. For pipe connections from DN350mm, no process evaluation and small series tests need to be carried out. This is mainly because the process for small diameter pipe fittings is more mature and the steel grade is inferior, etc. In summary, compared with small diameter pipe fittings, the requirements of large diameter pipe fittings are more stringent than that of small diameter pipe fittings. pipe fittings.

2.2 Testing the first batch of pipe fittings

(1) Technical data for PetroChina pipe fittings.
Section 5.2.3.3 of the PetroChina Technical Specification CDP-S-OGP-PL-011-2014-3 states that the first batch of pipe fittings produced shall be tested in accordance with the requirements of Annex B. Formal production may only occur after the qualification of the first batch tested. The supplier may no longer repeat the hydraulic burst test if there is verifiable documented information about the hydraulic burst test from the three years prior to the signing of the contract (Technical Specification CDP-S-OGP-PL-011-2014-3). Section 5.2.3 of the technical specification OGP-PL-010-2014-3 states that the first batch of pipe fittings produced must be tested in accordance with the requirements of Annex B and formal production can only take place after the first batch tested have been tested. been qualified. However, the technical specification does not mention the alternative requirement for hydraulic rupture tests. Technical specifications CDP-S-OGP-PL-011-2014-3 and CDP-S-OGP-PL-010-2014-3, Appendix B, require the following first batch testing: The first production of accessories using the same manufacturing process becomes 5 accessories selected for Richter hardness testing, optical quality testing and dimensions, as well as non-destructive testing. Of these, 1 pipe fitting part will be randomly selected for a chemical analysis of the pipe body, a tensile test, a Charpy impact test (tees and elbows must also pass a series of temperature impact tests), a guided bending test, a Vickers hardness test and a selected metallographic test. Of the remaining 4 pieces of pipe fittings, 1 piece is subjected to a hydrodynamic burst test.
(2) National standards for pipe fittings . The first round of inspection is optional.
(3) Comparative analysis. Pipe fittings manufactured in accordance with national standards do not need to undergo first batch testing. In PetroChina's technical specifications, testing of the first batch for production is required, regardless of diameter. Test quantities and first batch test designs are clearly defined. Pipe connections of DN400 mm are clearly exempt from the hydraulic burst test. DN350 mm pipe connections are not exempt from the hydraulic burst test. Pipe connections of DN350 mm are not exempt from the hydraulic burst test and must be subjected to a hydraulic burst test. For pipe connections with different specifications, PetroChina's technical specifications determine that larger diameter pipe connections are riskier and more expensive.

2.3 Group batch pipe fittings testing

(1) Technical data for PetroChina pipe fittings.
PetroChina CDP-S-OGP-PL-011-2014-3 Technical Specifications 8.1.2 Provisions: Single test, small batch production process, 1 piece of pipe connection shall be used for mechanical properties and metallurgical testing; formal production process, the same melting batch, the same heat treatment process, the difference in nominal billet wall thickness not more than 6mm of the same Type of pipe fittings for a batch of no more than 50 pieces, shall be 1 piece is removed from each batch for mechanical and metallographic properties testing. Technical Specification 5.2.3 CDP-S-OGP-PL-010-2014-3 stipulates that: In the formal production process, basically according to the same melting batch, the same heat treatment process, the same furnace batch of heat treatment and similar accessories as a batch, each batch must consist of 1 piece so that mechanical and metallurgical property tests can be carried out.
The test points of technical specification CDP-S-OGP-PL-011-2014-3 and CDP-S-OGP-PL-010-2014-3 are the same and include tensile test, Charpy impact test, weld-oriented bending, hardness testing and metallurgical testing for the specified pipe connection parts.
(2) National standards for pipe fittings . Standard GB/T 13401-2017 7.1.1.1.
Provisions: For the production of pipe fittings for 1 batch, use the same raw material quality, melting furnace number, similar raw material specifications (wall thickness difference no more than 6mm) and the same process heat treatment. The test points are the same as the CNPC technical specifications, including tensile test, Charpy impact test, weld-oriented bending test, hardness test and metallographic test on the specified parts of pipe joints.
(3) Comparative analysis. PetroChina Technical Specifications Group Batch Principle Needle
There are slight differences in the connections of pipes with different diameters. For DN400 mm and more, the nominal billet wall thickness is not more than 6 mm, for DN350 mm and less, the provisions for the same batch in the heat treatment furnace. This is mainly because pipe fittings with different specifications for heat treatment than small diameter pipe fittings can be placed in the same batch in the heat treatment furnace, which reduces the cost of group batch testing. Normally, the heat treatment process of large diameter pipe joints with different specifications (especially when the difference in wall thickness is large) is certainly not the same, so the performance of heat treated joints must be guaranteed after providing the range difference in wall thickness. PetroChina's technical specifications and national standards for group batch testing are the same, but the group batch principle is very different. For connections with DN400 mm and above, PetroChina technical specifications require similar connections; Although national standards require the same quality of raw materials, the same principles apply to the rest. Therefore, PetroChina's technical specifications are more stringent than national standards. 3.

3. The importance of PetroChina's strictest technical specifications

In recent years, there have been many accidents involving leaks in pipe connections at PetroChina gas stations and oil and gas pipelines. Due to the special characteristics of the petroleum industry that lead to the high use of compounds, and the fact that compounds in the petroleum industry are used in aggressive environments and other reasons, the probability of accidents is much higher than in other industries. For example, cracks in the main shoulder of the base material of a pipeline T-joint at the fill weld resulted in an accident that resulted in the entire pipeline breaking. At one project station, the breakage of the T-piece dosing slide caused accidents that had extremely serious consequences for society. These accidents resulted in extremely serious personal injuries and material damage, as well as economic losses for society. These factors have led to the need for the oil industry to develop technical specifications that are more rigorous and more appropriate to the industry than national standards. This is how PetroChina's technical specifications were created.

4. Current problems and recommendations for pipe joint inspection

(1) The meaning and applicability of selected test standards for pipeline connections.
National standards and CNPC technical specifications differ in terms of testing, elements to be tested and alternative arrangements. Buyers should appropriately adopt relevant standards according to their needs, and it is best to make relevant technical agreements according to their needs. CNPC technical specifications are more stringent than national standards, and the requirements of large-diameter pipe fittings are more stringent than those of small-diameter pipe fittings. PetroChina Technical Specifications for the Scope of Application of Butt Welded Steel Pipe Joints for Oil and Gas Pipeline Engineering, Joints Fabricated for Transmission of Natural Gas, Crude Oil, Refined Oil and Gas Pipeline Engineering Main Lines and Stations liquefied natural; national standards for the scope of butt-welded seamless steel joints and welded joints. From the perspective of applicability of standards, PetroChina's technical specifications are only applicable to pipe connections for oil and gas pipeline engineering in the petroleum industry. The national standard applies to pipe connections in various industries. In summary, the provisions of the CNPC technical specifications pay more attention to the actual situation of oil and gas pipeline projects, and many provisions relevant to the oil industry have been added. In general, the national standard is the basis for the development of CNPC technical specifications. The CNPC technical specifications are the application of the national standard in the oil industry. The two complement and reinforce each other. Therefore, the review of the CNPC technical specifications cannot be dissociated from national standards. The development and improvement of CNPC technical specifications should be carried out with full consideration of the review of national standards, and based on the usage characteristics of industry accessories, promptly modify and expand provisions suitable for the industry. Increase appropriate conditions for the industry.
(2) In some cases, the trial production of individual pipe fittings, the production of small batches of pipe fittings, the testing of the first batch of pipe fittings, and the testing of group batches of pipe fittings cannot be carried out separately.
Currently, some buyers only purchase a small number of pipe fittings, many of them less than 10 pieces. If the national standard cannot be used for single test production, small batch production, first batch test and group batch test, it is more reasonable. However, if PetroChina's technical specifications must strictly follow the pattern of single test → small batch production → first batch test → group batch test, this makes implementation more difficult for the manufacturer and increases procurement costs. If the purchasing volume is relatively small, it is recommended to carry out individual testing, small batch production, first batch testing and group batch testing according to the principle of “four in one!” All connections are made at once, and then group batches are made according to the principle of group batch testing.
(3) Products ready for processing often have little practical significance.
Mature products must strictly meet the requirements of individual testing, small batch production, first batch testing and group testing. Therefore, PetroChina's technical specifications for individual tests and small batch tests are exempt from the detailed exemption. For conventional products, manufacturers can generally comply with exemptions. PetroChina's technical specifications for first batch testing and hydraulic burst testing are exempt from regulations, resulting in fundamental savings in manufacturing costs.
(4) It is difficult to select a pipe joint inspection program.
The general production process of pipe fittings consists of seamless steel pipes or steel pipes welded through pressing, drawing, forging, extrusion, stamping and other processes. For some unconventional pipe fittings, such as 3D sheets, the factory generally chooses the method of hot bending the sheets to form. At this time, it is necessary to pay special attention to 3D curvature detection in accordance with the relevant standards for bends and cannot be detected in accordance with the standards for pipe connections. This is because every standard test design is based on the molding process. The test elements summarized by the test help identify the weak points of various molding processes.

5. Conclusion