DN15 Titanium Slip-On Flange ASME B16.5 Class 150

DN15 Titanium Slip-On Flange ASME B16.5 Class 150

DN15, or 1/2 inch, is the smallest size listed in ASME B16.5, and a slip-on flange in this size is rarely limited by its pressure rating. What decides whether the joint survives is the fit between the flange bore and the wall of the 1/2 inch seamless pipe it slides onto, and the two fillet welds that hold it there. This flange is machined from titanium in Grade 2 or Grade 7 and supplied with a raised face, ready to pair with a matching 1/2 inch seamless pipe.

The Pipe Wall Governs the Joint

A slip-on flange is located by the pipe, not by a machined socket, so the bore has to clear the pipe outside diameter with enough clearance to slide on cold and still leave a fillet to deposit. Schedule 10S pipe in 1/2 inch has a wall around 2.8 mm; schedule 80S is over 5 mm. On the thin wall the risk is burn-through and a concave fillet that cracks at the toe. On the heavy wall the flange absorbs much more heat and the raised face can distort enough to leak at the gasket line. Both are welding variables, not material variables, which is why the pipe schedule should be stated with the order.

Flange Data

Grade 2 or Grade 7

Grade 2 covers most of the work: seawater, brine, chlorinated cooling water, hypochlorite dosing and food grade lines, where the commercially pure metal passivates and stays clean. Grade 7 adds 0.12 to 0.25 percent palladium, which raises the breakdown potential in reducing acids such as hydrochloric and in hot chloride service where Grade 2 would begin to pit. For a DN15 line the cost difference is small, so the choice should follow the chemistry of the worst case rather than the normal case.

Class 150 is a rating at ambient temperature. As the line temperature rises the allowable pressure falls, so a hot 1/2 inch branch needs the rating table rather than the headline number. Titanium also has a low thermal expansion compared with stainless steel, which keeps the bolt load more stable through a heat up and cool down cycle.

Welding a DN15 Slip-On

Because the part is small, heat input per pass matters more than on a large flange. Tack the flange square to the pipe, check the face run-out with a straight edge, then weld the inner fillet first and the outer fillet second, alternating sides so the pull stays balanced. Keep the arc off the raised face. A chill ring or a damp cloth behind the hub holds the face flat, and a slow cool after the last pass avoids the hard, crack prone zone that air cooling can leave in thicker sections. Pickling after welding restores the passive film at the heat tint.

Inspection and Packing

Each lot is checked dimensionally against B16.5, positive material identified on the hub and traced to the heat number, and packed in a plywood case with the faces protected so the serrations arrive intact. Flanges are quoted by size, class, grade and pipe schedule, and matched gaskets and bolt sets can be added to the same shipment if the line is being built as a unit.

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