Flat head FH

A flat head is an end closure on a pressure vessel and one of its main pressure-bearing components. It serves a sealing function. Firstly, it forms the top and bottom ends of a cylindrical pressure vessel. Secondly, when a pipeline terminates and is not intended to extend further, a head is used to seal the pipe by welding. Products with similar functions to heads include blind flanges and pipe caps, but these two types are detachable, whereas a welded head is non-detachable. Matching pipe fittings include pressure vessels, pipelines, flanges, elbows, and other components.

At present, most pressure vessel manufacturers are separate from pressure vessel design institutes, and they rely on specialized head manufacturers to produce heads. Due to the mismatch between the provision in GB 150 (the minimum formed thickness of a head shall not be less than the nominal thickness minus the negative tolerance of the steel plate thickness) and the manufacturing process, as well as inadequate communication among vessel designers, procurement staff of pressure vessel manufacturers, and sales personnel of head manufacturers, it is easy to cause material waste in head manufacturing, and even disputes arising from the end user’s non-acceptance of the increased thickness and weight resulting from the head manufacturing process.

Design pressure P = 1.6 MPa, design temperature 200℃, inner diameter of the head Di = 1000 mm, corrosion allowance C2 = 2 mm, head material: 16MnR.

(2) Calculation: According to Table 4-1 of GB 150, for δn = 6~16 mm, [δ]t = 170 MPa is adopted; in accordance with GB 150, the shape factor K = 1.00 and the weld joint coefficient is taken as 1.0.

Design thickness of the head:

δd = δ + C2 = 6.72 mm

Steel plate negative tolerance C1 is taken as 0.25 mm, and the nominal thickness of the head δn is set at 8 mm.

Effective thickness of the head:

δc = δn − (C1 + C2) = 5.75 mm

δc > 0.15% Di = 1.5 mm, meeting the stability requirement.

Upon completion of the design process, the designer marks the head as EHA1000δ8-16MnR in accordance with JB/T 4746-2002.

Procurement personnel of the pressure vessel manufacturer issue the specification EHA1000×8-16MnR to a specialized head manufacturer for production based on the drawing.

After receiving the order, the head manufacturer uses 10 mm steel plates for production in accordance with the provisions of GB 150-1998 (the minimum formed thickness of a head shall not be less than the nominal thickness minus the steel plate negative tolerance), which is referred to as secondary process thickening.