Pipe caps and heads are two components commonly used to seal the ends of pipelines or vessels, with distinct differences in definition, manufacturing standards, pressure-bearing capacity, connection methods, and other aspects.
Definitions
●Pipe Cap: Also known as a plug or end cap, it is a pipe fitting welded to the pipe end or mounted on the external thread of the pipe end to seal the pipeline. It serves the same function as a pipe plug and is similar in form to a blind flange. Welded pipe caps are non-removable.
●Head: Also referred to as an end cover, it is a component used to seal the end of a vessel and isolate internal and external media. It is an indispensable core component of pressure vessels.
Common Materials
●Carbon steel, stainless steel, alloy steel, etc.
Common Implementation Standards
Pipe Cap
●ASME B16.9 "Factory-Made Wrought Buttwelding Fittings"
●EN 10253 (European Harmonized Standard)
●Other relevant international and national standards
Head
●ASME Section VIII Div.1 "Boiler and Pressure Vessel Code (BPVC) Section VIII Division 1"
●EN 13445-3
●DIN series
●Other relevant pressure vessel design standards
Pressure-Bearing Capacity
Pipe Cap
●Suitable for low-pressure service below PN16, generally not intended for high-risk media.
●Typically adopts Class or PN rating matching the pipeline system; no separate strength calculation is required, but it must be compatible with the pipeline's pressure rating.
Head
●Features a wide pressure-bearing range (PN16 to PN400 or higher).
●Requires verification through stress analysis and burst testing, and must be designed in accordance with pressure vessel design standards.
●Has strict requirements for materials and welding processes; material certificates and non-destructive testing (NDT) certificates must be provided.
Connection Methods
Pipe Cap
●Butt welding: Suitable for pipeline systems subjected to higher pressure and temperature.
●Socket weld: Suitable for small to medium diameters and medium to low pressure pipeline systems.
●Threaded connection: Suitable for small diameters and low pressure pipeline systems; easy to disassemble but with relatively lower sealing performance and strength.
Head
●Must be welded to the pressure vessel shell to ensure the strength and tightness of the entire vessel.
●Common welding methods include butt welding and fillet welding.
Application Fields
Pipe Cap
●Mainly used at the ends of various pipeline systems to seal pipelines, prevent medium leakage or the entry of foreign objects.
●Also commonly used for temporarily sealing unused pipelines.
●Widely applied in pipeline systems of petrochemical, electric power, construction, and other industries.
Head
●Mainly used at the ends of various pressure vessels, storage tanks, boilers, reactors, towers, and other equipment.
●Plays a key role in reaction vessels and storage tanks in the petrochemical industry, boilers in the electric power industry, and pressure vessels in the pharmaceutical, food, and other industries.
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