A–B–C–D–E–F–G–H–I–J–K–L–M–N–O–P–Q–R–S–T–U–V–W–X–Y
Hammer Blow
In electric actuators, it is a lost motion mechanism to allow a motor to reach full speed before engaging the gear drive. Provides a higher efficiency for overcoming valve break torque, but it does not produce more torque than the nominal actuator rating.
Handpump
Manually operated hydraulic pump used to provide hydraulic pressure.
Handwheel
Wheel consisting of a rim connected to a hub and used to manually operate a valve.
Handwheel Rim Pull
The manual effort (force) required on the rim of a handwheel to open or close the valve. Normally expressed in Newton Metres (Nm).
Hardfacing
A surface preparation such as Fusion Hardfacing detonation gun or High Velocity Oxy-Fuel (HVOF) in which a hard alloy is deposited on a metal surface to increase wear and/or corrosion resistance.
Hardness
In metallurgy, hardness is defined as the ability of a material to resist deformation usually by indentation. Hardness measurement can be defined as macro, micro or nano-scale according to the forces applied and the displacements obtained.
Hardness Test
A means of determining resistance to penetration. In the metal industry the most used tests are the Brinell hardness test, the Rockwell hardness test and the Vickers hardness test. These tests determine the resistance to the penetration of a non-deformable ball or cone by measuring the depth which such ball or cone sink into the metal under a given load within a specified period of time. ASTM A370 specifies procedures for Brinell Test and Rockwell Test.
HART
A bi-directional industrial field communication protocol used to communicate between intelligent field instruments and host systems.
Hazardous Areas
Locations where hazardous materials, sufficient in quantity to create an explosion, will require electrical equipment to have special protection to prevent causing an explosion.
Head
The vertical distance between two levels in a liquid.
Heat Affected Zone (HAZ)
Portion of the base metal which has not been melted, but whose mechanical properties or microstructure has been altered by the heat of welding or cutting.
Heat Analysis
A chemical analysis conducted by the foundry immediately prior to pouring which measures the exact chemical composition of a particular batch of molten metal. Does not include analysis of physical properties.
Heat Treatment
Describes any process or procedure by which the internal structure of steel is altered by heating to produce desired physical characteristics. This is usually accomplished by furnace heating followed by controlled cooling.
Heat Treatment Charts
Furnace charts providing a temperature against time record of the heating and cooling cycle required by a specific heat treatment process for a particular furnace load of steel or steel parts.
Helical Gears
Cylindrical in form with the teeth having a constant section and cut along a helix on the pitch diameter.
Hermetically Sealed
Enclosure constructed so that there is zero ingress of gasses, liquids or solids.
Hertzian Contact Area
The magnitude of the pressure at any specified location in a Hertzian contact area as calculated from Hertz’ equations of elastic deformation.
HIC (Hydrogen Induced Cracking)
A planar cracking that occurs in carbon and low alloy steels when atomic hydrogen diffuses into the steel and then combines to form molecular hydrogen at trap sites. Cracking results from the pressurization of trap sites by hydrogen. No externally applied stress is needed for the formation of hydrogen-induced cracks. It is usually associated with low-strength plate steels used in the production of pipes and vessels.
HIPPS (High Integrity Pressure Protection System)
An actuated valve and control system to protect against overpressure of pipeline risers.
Holiday
An imperfection or bare spot in a coating or plating.
Hot Isostatic Pressure (HIP)
Special forming process used to compact and metallurgically bond metal powder. This process takes place within a flexible, metal container whose contents are formed into the desired shape by subjecting the container to high temperature and pressure in an autoclave. It produces a fully wrought structure.
Hot Tapping
The process by which a pipeline under pressure is cut into to provide a side outlet. A flanged fitting is saddle welded to the pipeline and a full port valve bolted to the flange. The hot tapping machine bolted to the outboard valve flange operates through the open valve. After cutting out a circular piece coupon from the pipe wall, the coupon is removed from the pipe by retracting it through the valve and into the chamber of the tapping machine. The valve is then closed and the tapping machine and coupon are then removed from the valve.
HPU (Hydraulic Power Unit)
A device to create kinetic energy within a hydraulic system. Usually comprises a motor (Electric/Air/Engine powered) a storage tank, filters, regulators, directional valves, gauges etc. to power one or multiple valve actuators.
HSC (Hydrogen Stress Cracking)
Cracking that results from the presence of hydrogen in a metal and tensile stress (residual and/or applied). HSC describes cracking in metals that are not sensitive to SSC (Sulphide Stress Cracking), but which may be embrittled by hydrogen when galvanically coupled to another metal that is corroding actively as an anode.
Hub
Protruding rim with an external angled shoulder and a sealing mechanism used to join pressure containing equipment.
HVOF (High Velocity Oxy-Fuel)
A thermal spray technique used to deposit protective coating on a substrate. A blend of fuel (gaseous or liquid) and oxygen is injected into a torch and burned. The combustion products flow through a nozzle that accelerates the flow to a speed up to 1500 m/s. A powder feed stock is injected into the gas stream which accelerates the powder up to 800 m/s. The stream of hot gas and powder is directed towards the surface to be coated. The powder partially melts in the stream and deposits upon the substrate. The resulting coating has low porosity and high bond strength.
HWO (Handwheel Operated)
A valve on which the handwheel drives the stem directly to operate the valve.
Hydraulic
Pertaining to or using water, oil or other liquids.
Hydraulic Actuator
A device that converts hydraulic pressure into motion via a pressurized piston within a cylinder. This linear movement is converted into rotary movement for quarter-turn valves by a scotch-yoke mechanism.
Hydraulic Motor Actuator (Operator)
A device by which rotation of a hydraulically powered motor is converted into mechanical motion.
Hydraulic Seats
The movement of the seats in a valve is controlled by using water, oil or other liquids under pressure.
Hydrostatic Test
A test in which a valve is filled with water and pressure tested. According to ISO 14313 / API 6D, hydrostatic tests on a valve are:
- Hydrostatic Shell Test: done at a pressure 1.5 times the design pressure
- Hydrostatic Seat Test: done at a pressure 1.1 times the design pressure
Hyperbaric Testing
It is a simulated pressure and depth test.