Quality control of flange management
Flange is a connection component that has an important role in ensuring the tightness between pressure pipelines, valves and various types of equipment. Combined with the pressure pipeline construction of ICHTHYS module, the control measures of flange installation tightness are explained, mainly including material control, quality control in the welding process and quality control in the connection assembly. Through reasonable material selection, correct installation (implementation of standards and specifications) and safe operation, we can ensure the safe and stable long-cycle operation of production units.
Various types of pressure pipelines, valves and equipment are mostly connected in the form of flanges, and the operational safety of pressure pipelines is directly related to the quality of flange connections. Therefore, it is necessary to pay attention to and do a good job in flange management, Chen et al  pointed out the importance of flange seal management database construction and analysis, Deng Xianjun  analyzed the anti-corrosion construction management in LNG pipeline flange management, Wang Hongwei et al  did not involve the specific quality control in flange welding assembly and connection process, although they described the flange management of Majnoon project in Iraq. This paper is an effective combination of the construction practice of ICHTHYS module to explain the quality control of flange management in the construction process, mainly including material control, welding assembly and flange connection tightness.
Overview of flange management
Table of Contents
Flange management is a general term for activities such as flange piece storage, welding assembly, bolt tightening, site inspection, tagging and data preparation, etc. The whole process management is implemented within the scope of prefabrication, installation and construction, commissioning and operation stages. Its advantages are to realize strict inspection of materials, effectively control welding errors, standardize all kinds of installation operations, solve the leakage problem caused by uneven flange tightening, and thus improve safety performance.
As an important connecting part between pipes, valves and equipment, flanges have strict requirements on their own materials, and need to ensure the specification of materials from the source, and need to standardize the installation operation in the process:
- 1) When the flange is supplied, the material engineer will organize the acceptance to meet the design requirements [5-6] as the target, and the acceptance will include appearance, inner and outer diameter, bolt hole center distance and flange height, etc.
- 2) After the flange is accepted, it is necessary to take measures such as applying anti-rust oil and buckling flange cap in time, and then transported to the warehouse for storage.
- 3) Store flanges on shelves in separate areas, following the principle of stacking in layers and classifying, and marking well to facilitate material collection.
- 4) Receive materials as needed and pay attention to protect the sealing surface of flanges and prevent the loss of flange caps during the backward transportation of flanges.
Welding assembly control
1) Before welding the flange, its sealing surface should be inspected, including flatness inspection and finish inspection, and the flange with burr or radial groove should not be used.
2) Welding, the number of isometric spot welding needs to meet the standard, under general conditions, the pipe diameter ≤ 101.6mm, isometric spot welding number ≥ 3; pipe diameter > 101.6mm, isometric spot welding number ≥ 4. special conditions, the designated personnel need to check and advice, and finally determine the appropriate number of isometric spot welding.
3) When spot welding, use the horizontal ruler to detect the connection line of 2 relative bolts to ensure that the error is within the allowable range. For vertical installation, the bolt holes should be ridden across the vertical axis; while for horizontal installation, the screw holes should be ridden across the north-south axis.
4) In welding, the deformation deviation needs to be strictly controlled to ensure that the error after welding is within the permissible range, as shown in Figure 1, where the error range [7-9] of numbers ① to ⑥ are:
- ① The maximum allowable tolerance of ± 3mm;
- ② The maximum allowable error in the length direction is ±3mm;
- ③ The maximum allowable error of the maximum lateral deviation of the branch is ±1.5mm;
- ④ The maximum deviation of the bolt hole is ±1.5mm;
- ⑤ The tolerance of flange surface inclination is 0.6mm;
- ⑥ The maximum permissible angle tolerance is ±1°.
Figure.1 Schematic of welding error
Flange connection control
Flange connection control is also an important management content, including the standardized management of the entire flange data system, the training management of professionals and the installation management of construction practice.
Establishment of data system
- 1) Establish a flange management data system, and enter all information in the data system in categories and batches, including drawing number, pipe grade, joint node information (size and type), bolt information (size, quantity and material), gasket information (size and type), lubricant type, fastening method, joint node risk level, torque and tensile force value, etc., and implement dynamic management of the entered data information.
- 2) In flange management, supervision is classified according to different risk levels to achieve scientific and efficient supervision. When it comes to high-risk joint nodes and tensile joint nodes, the construction unit must be formally notified by the construction supervision, and only after receiving the witness permission from the construction supervision can the subsequent construction be carried out; when it comes to medium-risk joint nodes, the construction supervision randomly samples 10% from the system and implements the witness permission system, while the remaining 90% is monitored by the quality control inspectors commissioned by the construction supervision; when it comes to low-risk joint nodes, the construction supervision All entrusted to quality control inspectors for monitoring.
- 3) The flange management data system needs to record each connection detail in the form of joint node completion, providing complete information (date of assembly, gasket, bolt and nut specifications, torque/tensile force values, assembler’s name, name of the person responsible for witnessing the completion of the connection, hydraulic tool maintenance records and calibration records).
- 4) After the joint node is completed and received, the relevant signatory shall return the complete documentation to the system and submit it to the construction supervisor who will confirm the accuracy and completeness and update the system data.
- 5) Flange management hangtags are divided into red, orange and green, as shown in Figure 2. The red tag is to be removed after the flange management is completed, and the removal means that this joint node shall not be altered or damaged at will; the orange tag is to be removed after the seal test is witnessed by the owner during the pre-commissioning of the system, and the seal test record sheet is attached and entered into the data system; the green tag is to be kept on the flange.
Figure.2 Record sheet schematic
- 1) During flange construction, the installation and assembly of flanges shall be carried out by qualified professionals, while the training work and qualification of professionals shall be carried out by trainers appointed by the construction supervision.
- 2) The trainer prepares the assembly instruction steps of flange joint nodes, and the operators should be familiar with the important steps in advance and clear about the assembly ability and scope of assembly.
- 3) The participants are divided into 3 categories according to the assessment results, and their numbers and grades are marked with different tags. Among them, Grade I, the assemblers who are formally identified as qualified to assemble low-risk joint nodes; Grade II, the assemblers who are formally identified as qualified to assemble low- and medium-risk joint nodes; Grade III, the assemblers who are formally identified as qualified to assemble low-, medium- and high-risk joint nodes .
- 4) Quality control and inspection professionals should have the skills, knowledge and experience of each link to ensure that the operational links in the field are in accordance with the procedures.
Construction practice installation
1) The construction unit identifies the risk of flange joint nodes according to ISO drawings and selects the appropriate qualified assemblers.
2) The correct materials are used to ensure that the bolts used are not damaged or visibly rusted, that components, flanges, gaskets, bolts and nuts are clean and meet specifications, and that the lubricants used in the process are of a brand specified by the construction supervision, thus ensuring that the entire process meets project requirements and is standardized. The torque requirements for the bolts are shown in Table 1.
3) Using the equipment manufacturer’s manual and installation procedures as guidelines, torque wrenches or tensioners will be used to tighten the flanges. In special cases, if pneumatic or electric wrenches are required, they should be reported to and agreed by the construction supervisor.
Table.1 Bolt torque requirements
|Bolt specification / ″ (inch)||Material B7, L7 / nm||Material b8m grade 2 / nm|
Note:Take the friction coefficient of lubricant as 0.11, 1 inch = 25.4mm.
4) When tightening joint nodes, hammering method shall not be used.
5) Each pressure level range, 1-3/8 inch diameter and above joint node bolts, the preferred bolt tension method for tightening, bolt stress and torque values shown in Table 1, based on the standards [10-12] including A193-B7, A320-L7: 290MPa; A193-B8M Class2: 174MPa. torque should be based on the bolt oiling state and Friction coefficient should be selected.
6) First tighten the nut by hand/wrench, not exceeding 20% of the target torque, and check the uniformity of the flange gap on the circumference; if the circumferential gap is inconsistent, adjustments should be made before the tightening work.
7) Adopt the symmetry principle to tighten the bolts, and mark the correct tightening order in clockwise direction. The bolt is tightened in 3 times: the first tightening torque does not exceed 30% of the final torque, the second tightening torque does not exceed 70% of the final torque, and the third tightening reaches the final torque. In addition, the flange gap needs to be monitored during the tightening process, and the proper parallelism of the gap is maintained through the adjustment of the bolt sequence.
8) Change the sequence from diagonal to adjacent bolt sequence and tighten one by one along the flange perimeter with 100% of the set torque in clockwise direction, and confirm again that the nut does not turn.
9) For joint nodes that have been received but still require disassembly, report to the construction supervisor and receive permission to work while replacing the original placard, and after reassembly, resubmit to the system for documentation.
10) In the process of loosening the flange, use a torque wrench to gradually increase the removal torque, starting with the farthest bolt, then move the torque wrench to the symmetrically located bolt and repeat the operation until all the nuts evenly distributed along the circumference of the flange are loosened. In the process of loosening, the nut shall not be separated from the bolt immediately.
11) Slack or damaged flange joint nodes shall be considered as failure, and their tags shall be removed and torn off, and the end item of the treatment requiring reassembly shall be proposed according to flange management.
12) If a joint node has no placard or carries an exception placard, the joint node shall be considered unfinished and shall be reassembled.
13) Flange placard shall carry detailed information, its number shall be identified on the end item, the record shall be resistant to the environment and not fade, and the placard shall be tied to the joint node or nearby location.
14) The joint shall not be reusable and shall be manually connected, shall be with self-locking function and its minimum breaking strength shall not be less than 20kg.
15) Each flange joint node shall have independent and unique and the same labeling as ISO drawing. The joint node belonging to the scope of flange management shall have a unique and independent label attached by the flange assembler.
Author:Ma Zhijie, Yang Qing, Wu Xue
Source: China Flanges Supplier: www.epowermetals.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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