In ultra-pure and corrosive fluid-handling environments, the smallest variation at a tubing connection can become a leak path, a contamination risk, or a repeatability problem. That is why tubing end formation matters as much as tubing material selection. When fluoropolymer tubing (commonly PFA or FEP) is used with flare-style fittings, hot flaring mandrels help produce a consistent flare geometry that supports reliable sealing and predictable assembly results.
Below is how hot flaring mandrels support quality, what “good” looks like in practice, and how teams can reduce variability when flaring tubing in the field or on the production floor.
What “hot flaring” is and why it’s used
Hot flaring is a controlled heating and forming process that permanently expands the tubing end into the flare profile required by the fitting system. In many high-purity flare fitting systems, the flare is created with an external heat source (often a heat gun) and a forming mandrel.
This matters because the flare end is the interface that ultimately helps create the seal. If the flare is uneven, overheated, underheated, or formed inconsistently, sealing performance becomes less predictable.
Why mandrels improve flare consistency
1) They standardize flare geometry
A properly designed mandrel acts as a fixed “mold” for the flare shape. When the tubing is heated and seated to a defined stop/shoulder on the mandrel, the operator is far less reliant on feel or guesswork to achieve a repeatable flare length and profile. Parker’s flare-fitting instructions, for example, describe heating, then pushing the tubing over the correct flaring mandrel until the end reaches the mandrel stop shoulder, and holding until cool.
2) They reduce circumferential variation from uneven heating
One of the biggest sources of poor flare quality is inconsistent heating around the tubing circumference. A well-known issue with purely hand-held heat-gun flaring is that uneven heat application can reduce repeatability and introduce quality-control challenges.
Mandrels don’t replace heating, but they reduce what “variation” can turn into by forcing the final formed shape to conform to a consistent geometry.
3) They support controlled cooling and stress reduction
In higher-throughput flaring systems, mandrels can also play a role in how heat is extracted from the formed end. Some engineered flaring systems describe mandrels designed to extract heat evenly after forming, helping create a more “stress-free” formed flare end.
Even when you’re not using an automated system, the principle holds: consistent forming and consistent cooling time reduce the odds of distorted flare shapes.
What a “quality flare” looks like
You don’t need a microscope to catch most flare issues. Here are the practical indicators teams commonly use to assess flare quality during assembly:
- Symmetry: flare should be even around the full circumference (no lopsided “thin side / thick side”).
- Smoothness: inner and outer surfaces at the flare should be clean and uniform (no tearing or rough edges).
- Correct flare length: flare should match what the fitting design expects, minimizing dead volume and supporting full engagement. (Many flare fitting systems emphasize leak-tight connections with minimal dead volume when assembled correctly.)
- No overheating indicators: signs of scorched, overly softened, or distorted tubing at the flare zone suggest excess heat or dwell time.
A repeatable hot-flare workflow
While each fitting system and tubing size has its own best practices, a common, repeatable workflow looks like this:
- Cut tubing cleanly and square to support even forming.
- Heat the tube end consistently (some instructions call for rotating the tube while heating to promote uniformity).
- Immediately form on the correct mandrel to the defined stop/shoulder.
- Hold until cooled so the flare “sets” in the correct geometry.
- Inspect the flare (symmetry, smoothness, proper length), then assemble the fitting.
If you’re seeing inconsistent results, the most common culprits are: uneven heat application, inconsistent timing, wrong mandrel sizing, or rushing the cool-down step (which can allow the flare to relax or deform).
One-of-a-kind flaring equipment from Crist Group
At Crist Group, we build and support flaring solutions for industries that can’t afford leaks, inconsistency, or downtime. When you’re working with PFA and FEP tubing in industrial and fluid-handling environments, precision flaring is what helps create leak-proof, high-performance connections. Poorly flared tube ends can lead to leaks, inefficiencies, and costly system failures, which is why we focus on tools designed for repeatable results.
We offer hot flaring mandrels for PFA and FEP tubing designed for accuracy and ease of use, featuring ergonomic handles for portable use (with optional bench mounting) and compatibility from ¼” to 1″. Our mandrels are available as a full-size kit (¼”, ⅜”, ½”, ¾”, 1″) or as individual sizes, and they’re built around simple insertion of preheated tubing for reliable flares. Each mandrel includes a handle for flexibility across applications.
If you’re trying to standardize flare quality, reduce rework, or equip your team with dependable flaring tools, we can help you choose the right mandrel size and tool type for your tubing and application. Contact Crist Group to talk through your requirements and get the right flaring setup in place.
