Important technical terms

Hardening test
For the hardening test, a standardized hardened or diamond indenter is pressed into the material to be tested with a certain test force during a determined exposure time. The respective depth of penetration and/or indentation surface (impression) is referenced as measure for the hardness of the material/component.

Heat exchanger
A heat exchanger is a plant, which transfers the thermal energy from one medium to another. Heat exchangers are very often used to utilize idle energy, e.g. of an exhaust gas, for pre-heating of combustion air and thus achieve a higher efficiency. In other cases, a circulating (radioactive) medium is not to leave the circuit and the energy is transferred to a medium harmless for further processing. Mostly tube or plate heat exchangers are used, whereat the heat transfer from one medium to the other takes place by means of heat conduction via the separating plate/tube walls.

Heat-resistant steel
In case unalloyed steel is exposed to gaseous aggressive media (air or combustion gases) at temperatures of over 550 °C, they scale at the surface and permanently offer new reaction possibilities with the flaking of the scale. By adding chromium in contents of about 3 to 28 %, scaling is inhibited. This behavior is still enforced by addition of silicon and aluminum. In an oxidizing atmosphere, the three elements form tight and adherent coatings, which inhibit further scaling. These layers have to be elastic, so that they are not destroyed by the material expansion caused by heating. The upper limit of resistance is about 1,200 °C. For an increase of the high-temperature strength and continuous stressability, Ni in graded contents of about 8 to 35 % is added, to make the steel capable to sustain simultaneous mechanical stresses.

High-pressure pipes
High-pressure pipes means pipes, which are stressed with internal pressures of more than about 500 bars (= 50 MPa).

High temperature steel
Steel, which has good mechanical properties (creep strain limit, rupture strength, etc.) under long-term load (> 1000 hours) at temperatures of up to about 540 °C.

Hold Point
That means a holding point marked on the route card during or after a certain activity, at which an examination or investigation is required, before further processing is possible. Holding points have to be confirmed by the signature of the person authorized for that or a person representing him/her.

Hollow
Hot- or cold-manufactured tube, which is used as starting tube for a subsequent forming step or a tube, which is not finally dressed and straightened.

Hollow bar
Hollow bars are thick-walled, extruded, from case to case also cold manufactured tubes. Hollow bars serve as starting material for ring- and sleeve-shaped construction elements and offers substantial cost benefits compared to solid material.

Hot-formed tube
Is a tube manufactured by billet extrusion. The forming temperatures of the extruding press lie between 1050 °C and 1250 °C, depending on the material and finished tube dimensions.

Hot tension test
In the hot tension test, a tension sample is stretched until fracture at a certain (constant) temperature; the drawing stress required for that is measured. The hot tension test serves the determination of characteristic material values like yield limit, tensile strength, fracture elongation, etc. at a certain temperature.

Huey Test
The Huey Test is a corrosion test for the determination of resistance against inter-crystalline corrosion. First of all, the sample is carefully weighed, a surface determination is executed and afterwards it is boiled in a test solution for 5 periods of 48 hours each. After each period (48 h) the weight is determined and at the end the removal rate is calculated. There is resistance against inter-crystalline corrosion, when the determined removal rate does not exceed a defined, critical limit value.

Hydraulic pressure test
The hydraulic pressure test is used for the examination of tightness and resistance against high internal pressures in seamless stainless pipes. The respectively required pressure and/or the required holding period are determined by the respective standard. In the internal pressure test executed for examination of tightness according to DIN 50104, the test pressure is 50 bars and is to be maintained for at least 5 seconds.