A welding neck flange (also called a &#;weld neck flange&#;) is well recognised for its long-tapered hub, which provides mechanical strength (useful to resist &#;dishing&#; and &#;bowing&#;). Welding neck flanges are high integrity flanges and are available in all sizes, all common face types (flat, raised, RTJ), and all classes. Due to the strength of the hub and the integrity of the weld, this type of flange is well suited for elevated temperature and pressure applications.
Welding Neck Flange Cross Section
A butt weld, also known as V-weld or groove weld, provides single full weld penetration and is used to connect the welding neck flange to a pipe or fitting. The single full weld penetration makes this type of flange suitable for severe operating conditions, such as high-pressure systems, sub-zero temperatures, and elevated temperatures. Other welding neck flange benefits include:
Welding Neck Flange
The unrestricted flow and low turbulence characteristics of a welding neck flange are linked to the low pressure drop across the flange; this is because the flange bore is the same as the pipe bore. Erosions rates are also linked to the pressure drop across the flange, although the erosion rate depends heavily upon what is flowing through the flange.
This type of flange has one significant disadvantage compared to other flange types, it is more expensive (a deciding factor for most companies).
Non-Destructive Testing (NDT) Techniques
A phased array (ultrasonic NDT technique) flange face corrosion inspection can be conducted on welding neck flanges; the results reveal any internal damage on the sealing face.
Magnetic particle inspection (MPI), dye penetrant inspection (DPI), radiographic testing (RT) and/or ultrasonic testing (UT) can be used to prove the butt weld.
ASME Standards
The standards ASME B16.5 and ASME B31.3 specify the requirements for welding neck flange installation, maintenance, and testing.
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https://en.wikipedia.org/wiki/Weld_neck_flange
https://www.texasflange.com/weld-neck-flanges
1. Limited flexibility:
One significant disadvantage of a weld neck flange is its limited flexibility. Due to its design, which includes a long tapered hub, it becomes challenging to accommodate piping systems that require angular or rotational movements. The inflexibility of a weld neck flange often necessitates tedious and time-consuming modifications to the piping system, making it less suitable for certain applications.
2. Higher installation time and cost:
Compared to other types of flanges, such as slip-on or threaded flanges, the installation of a weld neck flange requires more time and effort. The welding process involved in attaching the flange to the pipe requires skilled labor, specialized equipment, and compliance with strict safety regulations. Additionally, the welding process increases the overall cost of installation, which can be a significant drawback for projects with tight budgets.
3. Vulnerability to stress concentration:
Weld neck flanges are susceptible to stress concentration, particularly around the welded joint area. The high stress levels can lead to fatigue failure and cracks, endangering the integrity of the entire piping system. To minimize stress concentration, proper welding techniques, such as back purging and post-weld heat treatment, must be employed. However, these additional steps can further increase the time and cost of installation.
4. Prone to corrosion at the weld joint:
5. Difficult to disassemble and replace:
6. Limited compatibility with different pipe sizes and schedules:
7. Challenging to work with in tight spaces:
The long and tapered hub design of a weld neck flange can be challenging to work with in tight spaces, such as equipment with limited access points. The extended length of the flange requires sufficient clearance for proper installation and welding, which may not always be available. In such cases, alternative flange types that offer more compact designs, such as slip-on or socket weld flanges, may be more suitable.
8. Weight and size considerations:
Weld neck flanges are generally heavier and larger compared to other types of flanges. Their robust design, intended for high-pressure and high-temperature applications, often results in increased weight and size. This can pose logistical challenges during transportation and installation, especially in projects with limited lifting capabilities or space constraints.
9. Higher risk of thermal fatigue: