Technical analysis of titanium flange selection: Slip On Flange vs Socket Weld Flange

In today’s highly competitive and technically demanding industrial field, petroleum engineering projects have always been at the core, and their performance requirements for various materials and equipment are extremely demanding. Recently, our company received a technical consultation letter from a petroleum company, which is not accidental. With the continuous development of the petroleum industry, the safety and stability requirements for engineering pipeline systems are getting higher and higher, and the rationality of the selection of titanium flanges as key components of pipeline connections is directly related to the operation effect of the entire pipeline system.
The core topic of this consultation letter focuses on the selection of titanium flanges in engineering pipeline systems, specifically involving the technical comparison between titanium slip on flanges and titanium socket welding flanges. In petroleum engineering projects, pipeline systems need to withstand high pressure, high temperature and complex media environments, so the performance requirements for flanges are extremely high. Titanium alloy, as a new type of material, has become the preferred material under harsh working conditions such as chemical industry and marine engineering due to its lightweight, corrosion resistance and high strength. However, in the face of a variety of flange types, it is far from enough to rely solely on experience or simple comparisons, and systematic technical evaluation is particularly important.
Take an offshore oil extraction platform as an example. Its pipeline system needs to be in a high-salt, high-humidity marine environment for a long time, and it also has to withstand huge pressure and temperature changes. In this case, choosing a suitable titanium flange is crucial to ensure the safe operation of the pipeline system. If the selection is inappropriate, it may cause leakage, corrosion and other problems at the flange connection, which will not only affect the efficiency of oil extraction, but also cause serious pollution to the marine environment.

Ⅰ. Overview of titanium flange types and application scenarios

1. Titanium Slip-On Flange

Before understanding the titanium slip-on flange, we need to understand its origin and development. Flat welding flange, as a traditional flange connection method, has a long history. With the emergence of titanium alloy materials, titanium slip-on flange came into being. It is inserted into the pipe end through the annular socket and welded and fixed. This structural design makes it suitable for medium and low pressure (PN≤10MPa) pipeline systems.

From the structural characteristics, the annular socket design of the titanium slip-on flange makes it more convenient and quick to install. It can be directly sleeved on the pipe end and then fixed to the pipeline by welding. This installation method does not require complex processing of the pipeline, which greatly reduces the installation cost and time. For example, in some small chemical companies, due to the low pressure of the pipeline system, the use of titanium slip on flanges can quickly complete the connection of the pipeline, improving production efficiency.

The advantages of titanium slip on flanges are also reflected in low processing costs and convenient installation. Due to its relatively simple structure and mature processing technology, the processing cost is relatively low. At the same time, it is suitable for standardized connections under conventional environments, and it is a very economical and practical choice for some occasions where the connection requirements are not high. For example, in the water supply pipeline system of some cities, titanium slip on flanges can meet the basic requirements of pipeline connection while reducing engineering costs.

However, titanium slip on flanges also have certain limitations. Its pressure bearing capacity is limited, which is determined by its structural characteristics. Under high pressure, the annular socket and welding may not be able to withstand excessive pressure, and leakage and other problems are prone to occur. In addition, when exposed to corrosive media (such as chloride ion environments) for a long time, titanium slip on flanges need to strengthen surface protection. Chloride ions are highly corrosive and will corrode the surface of titanium alloys, thereby affecting the service life of the flange. For example, in some chemical companies in coastal areas, due to the large amount of chloride ions in the air, if the titanium slip on flange is not effectively protected, corrosion may occur in a short time.

2. Titanium Socket-Weld Flange
The emergence of titanium socket-welded flange is to meet the needs of some special working conditions. Its structural feature is that the pipe end is inserted into the socket hole and then double-sided welding is performed. This design makes it suitable for small-diameter (DN≤40mm) high-pressure scenes, especially in the petrochemical field.

In the field of petrochemicals, the pipeline system needs to transport various high-pressure and high-temperature media, and the sealing and vibration resistance of the flange are extremely high. The double-sided welding structure of the titanium socket-welded flange can ensure that the connection between the pipe end and the flange is more firm, effectively improving the sealing. At the same time, it has strong vibration resistance and can operate stably for a long time under high temperature and high pressure conditions. For example, in the pipeline system of an oil refinery, due to the fast flow rate of the medium in the pipeline, large vibration will be generated. The titanium socket-welded flange can effectively resist this vibration and ensure the safe operation of the pipeline system.

However, titanium socket welding flanges also have their own limitations. Its welding process requirements are high, because its double-sided welding structure requires more precise welding technology. If the welding is improper, defects may occur at the weld, which will affect the connection reliability of the flange. Therefore, during the welding process, it is necessary to strictly follow industry standards such as ASME B16.9. These standards have detailed provisions for welding processes, welding materials, welding parameters, etc. Only by strictly following the standards can the connection quality of titanium socket welding flanges be ensured.

Ⅱ. Differentiation analysis of titanium slip on flanges and socket welding flanges

Titanium slip on flanges Vs socket welding flanges

1. Titanium Slip-On Flange
The applicable scenarios of titanium slip on flanges are mainly in pipeline systems that are not frequently disassembled. For example, auxiliary pipelines or land tank connections on offshore platforms. On offshore platforms, auxiliary pipelines usually do not need to be disassembled frequently, and the sliding design of titanium slip on flanges can adapt to the displacement caused by thermal expansion and contraction, reducing stress concentration. The temperature of the marine environment varies greatly, and the pipeline will expand and contract with the change of temperature. If the ordinary flange connection method is used, the stress caused by thermal expansion and contraction may cause damage to the flange connection. The sliding design of the titanium slip on flange can effectively solve this problem. It can slide freely within a certain range, thereby releasing the stress caused by thermal expansion and contraction.

In terms of technical points, the titanium slip on flange needs to be matched with a high-precision bolt group (such as ASTM A192 grade) to ensure the uniform distribution of the tightening torque. The high-precision bolt group has higher strength and precision, which can ensure that the torque applied by the bolt during the tightening process is evenly distributed on the flange. If the tightening torque is uneven, it may cause leakage and other problems on the flange sealing surface. For example, in some large chemical plants, due to the high pressure of the pipeline system, the sealing performance of the flange is required to be very high. The use of a high-precision bolt group can effectively improve the sealing performance of the flange and ensure the safe operation of the device.

2. Titanium Socket-Weld Flange
Titanium socket-welded flange is preferred for high-purity medium transmission (such as the pharmaceutical industry) or highly corrosive marine engineering environments. In the pharmaceutical industry, the purity of the medium is extremely high, and any small leakage may affect the quality of the drug. The full penetration structure of the titanium socket welding flange can minimize the risk of leakage and ensure the purity of the medium. In the marine engineering environment, ordinary flanges are easily damaged by corrosion due to the strong corrosiveness of seawater. The corrosion resistance of the titanium socket welding flange can effectively resist the erosion of seawater and extend the service life of the flange.

In terms of technical points, the heat input needs to be controlled during the welding process to avoid the grain boundary β phase transformation of the titanium alloy in the range of 400-600℃, which leads to a decrease in toughness. In this temperature range, the internal structure of the titanium alloy will change, resulting in a decrease in toughness. If the heat input is too large during the welding process, the local temperature of the titanium alloy will rise to this range, thereby affecting the performance of the flange. Therefore, during the welding process, it is necessary to adopt appropriate welding processes and welding parameters to strictly control the heat input. For example, when welding titanium socket welding flanges, pulse argon arc welding and other processes can be used. This process can effectively control the heat input and ensure the welding quality.

Ⅲ. Selection decision recommendations

Pressure-caliber matching
When selecting titanium flanges, pressure-caliber matching is an important consideration. When DN≤40mm and PN≥10MPa, socket welding flanges are preferred. This is because the structural characteristics of socket welding flanges enable them to withstand higher pressures. For small-diameter and high-pressure pipeline systems, socket welding flanges are a more suitable choice. For example, in some high-pressure gas transmission pipelines, due to the small diameter and high pressure of the pipeline, the use of socket welding flanges can ensure the safe operation of the pipeline system.

When DN>40mm or PN≤10MPa, flat welding flanges can be considered. Flat welding flanges have low processing costs and convenient installation. For large-diameter or medium- and low-pressure pipeline systems, flat welding flanges can meet the connection requirements and reduce engineering costs. For example, in some urban drainage pipeline systems, due to the large diameter and low pressure of the pipeline, the use of flat welding flanges can effectively reduce the project cost.

Environmental adaptability
In different environments, titanium flanges need to have different environmental adaptability. In the environment containing H₂S and Cl⁻ media, it is recommended to use TA2/TA3 grade titanium alloy flanges of ASTM B348 standard. H₂S and Cl⁻ are highly corrosive, and ordinary flanges are easily damaged by corrosion in such environments. TA2/TA3 grade titanium alloy flanges have good pitting resistance, which is 3-5 times higher than that of 316L stainless steel. For example, in some sour gas fields in oil production, since the medium contains a large amount of H₂S and Cl⁻, the use of TA2/TA3 grade titanium alloy flanges can effectively resist corrosion and extend the service life of the flange.

Economic analysis
From an economic point of view, the initial cost of slip on flanges is low (about 70% of socket welding flanges). This is because the structure of slip on flanges is relatively simple and the processing technology is relatively mature, so the processing cost is relatively low. However, the maintenance cost of slip on flanges throughout their life cycle may increase significantly due to corrosion leakage. Due to the relatively poor sealing performance of slip on flanges, corrosion leakage and other problems may occur during long-term use, requiring frequent maintenance and replacement, thereby increasing the maintenance cost of the entire life cycle. Although the initial cost of socket welding flanges is high, their sealing performance is good, corrosion resistance is strong, and the maintenance cost of the entire life cycle is relatively low. For example, in some large chemical projects, although the initial investment of socket welding flanges is large, in the long run, the cost of its entire life cycle is lower.

Conclusion

The selection of titanium flanges is a complex process, which requires comprehensive consideration of multi-dimensional factors such as working pressure, medium characteristics and economy. In the actual selection process, it is recommended to combine ASME B16.9, HG/T20592-2009 and other standards for finite element simulation (FEA) to quantitatively evaluate the stress distribution of flanges under alternating loads. Finite element simulation can simulate and analyze the stress distribution of flanges under different working conditions through computer software, thereby providing a more scientific basis for selection.

As a professional titanium flange manufacturer, our company has rich experience and a professional technical team. We can provide customers with customized technical solutions and third-party testing services. According to the specific needs of customers, we can design the most suitable titanium flange selection plan for customers. At the same time, we can also provide third-party testing services to ensure that the titanium flanges we provide meet the relevant standards and requirements. Through our services, we help customers achieve safe and economical engineering goals and provide strong guarantees for customers’ engineering construction. In the future development, we will continue to improve our own technical level and service quality to provide customers with better products and services.