The More You Know – Nozzles!
In the oil & gas industry, nozzles are the connections on heat exchangers and pressure-vessels which allow the process to flow in and out. They can also be used for venting, draining, inspection, instrumentation, and other things.
Nozzles are defined by their size, flange rating, flange type, wall-thickness, projection, and material. While they are made up of very standardized parts, they are overall quite unique.
For example, the sketch of the nozzle on left could be defined as:
8”-300# RFWN, SCH XH, 12” projection
Materials: SA-350 LF2 Cl1 flange, SA-333-6 neck, and SA-516-70N re-pad.
Nozzle size and wall-thickness (schedule) are based on US standard pipe sizes under the ANSI standard (B36.10 for carbon steel and B36.19 for stainless and other alloys). Here is a small piece of a much larger table:
In the first column, the nominal pipe size is listed, followed by the actual outside diameter in the second column. The remaining columns specify the pipe thickness for a given schedule, from schedule 5 to schedule XXH. For both engineering and fabrication reasons, we mostly use nozzles about a ½ inch thick or thicker, which generally means schedule XH or greater. In the above table, an 8”-XH pipe has a thickness of 0.5 inches.
Nozzle flange ratings are defined under ASME B16.5 for sizes up to 24” and B16.47 for sizes over that. We reference the following table for carbon steel flanges:
In this table, I have highlighted the material grades A105 and A350 (aka SA-105 and SA-350), and the flange ratings 150#, 300#, and 600#. Higher flange ratings can be used for higher pressures and/or higher temperatures. 400# is never used in our industry.
Flange type – Our nozzles are usually RFWN or RFLWN types:
- Raised-Face Weld-Neck (RFWN) type nozzles have a forged flange welded to a short length of pipe. The weld-neck flange needs to have the same nominal pipe size and schedule as the pipe it is connected to. This configuration often requires a re-pad (circular plate) welded to the shell for reinforcement. For this type of nozzle, there are three different material grades:
- Flange – Forging, typically SA-350-LF2 Cl1.
- Neck – Pipe, typically SA-333-6
- Re-pad – Plate, typically SA-516-70N
- Raised-Face Long-Weld-Neck (RFLWN) is made up of a single forged piece. The advantage of this nozzle type is that they are `self-reinforced’, which means that a re-pad can be avoided, and thus cutting, fitting, welding, and inspection is reduced. While the flange is standardized, the nozzle neck (body dimensions) are customizable to meet the design requirements.
Several different configurations are shown below:
RFLWN and it’s HB and `Equal barrel’ variants do cost more upfront than RFWN, but they are more economical when factoring in labour and other costs
- There are other types of raised-face (RF) flanges noted below, but they are less commonly used on heat-exchangers in our industry (with exception for the blind flange which is used to close up and seal RFWN and RFLWN flanges).
- For the sake of a two-page article, I have skipped over other flange face types (RTJ) and special nozzles like Bluesky connections. Next month I plan to cover air-cooler winterization (recirculation).
