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Heat Treatment

heat- treatment

Equipment and Appliances for Heat Treatment

1. Equipment and appliances for pre-heating

Preheating may be carried out either in heat treatment equipment or by means of mobile heating appliances,e.g.gas burners or electrical induction or resistance heating appliances as applicable(resistance mats).A condition of their use is that the prescribed preheating and interpass temperatures must be capable of being kept constant and monitored throughout the welding operation.The temperature may be monitored by means of suitable appliances or aids, e.g.contact thermometers, temperature sensors or temperature-sensitive crayons.
2. Fixedheat-treatmentequipment(heat treatment furnaces)
2.1The fixed heat-treatment facilities (heat treatment furnaces) must be of suitable size for the
particular components and structures in question and be fitted with an appropriate temperature control facility.The furnaces must ensure that the particular heat treatment temperatures stipulated can be guaranteed and that the temperature is evenly and accurately controlled (DIN 17052,quality grade C).
2.2An adequate number of temperature recorders shall be provided,subject to a minimum of 2 to each furnace.The temperature variation over the period shall be established and recorded.    The temperature control device and the temperature and time recording instruments used shall be checked at regular intervals(at least once a year)and documentary proof of the inspection results submitted to the society on request.
3.Principles Relating to Heat Treatment
1.Heat treatment,temperature measurements and recording shall be performed by competent personnel.For this and the performance of heat treatment operations,of European draft Standard "Welding,quality requirements relating to heat treatment in conjunction with welding and forming".
2. The type,temperature and duration of the heat treatment process, in addition to the rates of
heating and cooling are determined by the material,the thickness of the material, the production process and the nature of the component or structure.
3.Details of the pre- weld heat treatment and post-weld heat treatment of a component or structure shall be included in the production documents submitted for inspection by the Society.Where the manufacturer’s welding procedure specifications(WPS)are used,these shall contain the necessary information relating to preheating, heat input during welding and post-weld heat
4. The whole of the component is normally subject to post-weld heat treatment.The heat treatment of part or sections of welds or the heat treatment of partial areas,especially pressurized components,require the Society’s consent in each individual case.A specification relating to this shall be submitted to the Society for examination.
5. Where welded joints are to be produced between different materials,in the case of complex
welded components (e.g. LNG/LPG process pressure vessels andgas tanks), components which have high levels of cold forming(more than 3 %)or extensive structural and repair welds to castings,the need for, type and extent of any heat treatment shall be agreed with the Society.
6.Parts shall be prepared for heat treatment in due order.Flange facings and sealings must be adequately protected against scaling. Precautions shall be taken to protect against component
distortions; components and structures shall be positioned accordingly.Unacceptable temperature gradients during the heat treatment process and during heating and cooling shall be avoided.



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