Local heat treatment residual heat stress control method of spherical vessel
Technical field
The invention relates to heat treatment technics, particularly a kind of local heat treatment residual heat stress control method of spherical vessel.
Background technology
Spherical vessel is widely used in belonging to large-scale pressure-bearing special equipment in the industries such as oil, petrochemical industry, chemical industry and municipal administration.In use, defect risks such as crackle often appear in spherical vessel, need carry out REPAIR WELDING.Because the inherent characteristics of welding process, welding residual stress certainly leads to, and because the spherical tank wall thickness is bigger usually, and binding force is strong, and the unrelieved stress that repair welding brings can reach the yield strength of material usually, equipment safety operation is constituted potential threat.Therefore need heat-treat and eliminate welding residual stress.
Usually adopt the partial heat treatment mode to eliminate the unrelieved stress that repair welding brings in the engineering, at D. La Dayi work, " welding effect: temperature field, unrelieved stress, distortion " (China Machine Press that translate in bear capital etc., July in 1997 the 1st edition) think in, in most of the cases, after the partial heat treatment, unrelieved stress is only to outer displacement.Zhang Yiliang etc. are by adopting the X-ray diffraction method, contrast test a 2000m
3The unrelieved stress of 8 measuring points before and after the spherical vessel partial heat treatment, show that the each point mean stress is 243.8MPa after the thermal treatment, compare before with thermal treatment, only descended 22.8%, and the position unrelieved stress of repair welding does not also improve after partial heat treatment to some extent, rises to 479MPa (2000m by 468MPa
3The inservice pressure vessel stress state is analyzed, test mechanics, 2001,16 (3): 276-282).Zhang Yiliang etc. pass through a 1500m
3The difference of two kinds of different case heat treating method test results of spherical vessel, draw local repair postwelding rectangle heat hot processing back (heated perimeter 400 * 600mm) among a small circle, unrelieved stress still near or reach the yield strength of material, illustrate that partial heat treatment do not play effect; And adopt the domain heating unrelieved stress can be reduced to 50% original (1500m
3The lpg spherical tank analysis of Residual Stress, petrochemical equipment, 2004,33 (6): 9-12).These cases show, eliminate welding residual stress by partial heat treatment and also do not reach gratifying effect.
The regulation of identical spherical shell partial heat treatment is disclosed in three bundlings of U.S.'s " ASME boilers and pressure vessel standard " VIII volume, " the heat penetration zone " of pointing out partial heat treatment (soakband) should be circular, and its radius should exceed the smaller value among the repair welding thickness of slab in zone and 2 inches (51mm).Here " heat penetration zone " refers to that temperature meets or exceeds between the metal area of regulation thermostat temperature.Because " heat penetration zone " can not think the local heating zone simply in the partial heat treatment process, therefore this requirement is not easy to use in engineering.Even therefrom find to satisfy fully the regulation of ASME, residual thermal stress still can reach the yield strength of material, and this regulation that shows ASME can not instruct engineering reality.
China's concerned countries standard and special equipment technical specification of security are all less than the regulation about the spherical vessel partial heat treatment.In fact domestic research to the spherical vessel partial heat treatment at present still is in the case state, still lacks sophisticated experience, does not also carry out systematic study.The partial heat treatment effect assessment once just needs tens thousand of units (common more than 30000 yuan) in the engineering, and most of user's financial insolvencies make processing parameter select to be in blindly state, can't guarantee heat treated effect.
Generally, for prevent that unrelieved stress from bringing such as major accidents such as stress corrosion crack and brittle ruptures, unrelieved stress should be controlled at the material yield ultimate below 40%.Because spherical vessel develops to maximization and high-parameters direction at present, the a large amount of Hi-Stren steel that adopt of beginning are made spherical vessels, and along with the deterioration of international petroleum quality, strict more to the requirement of unrelieved stress, under the certain situation, unrelieved stress need be reduced to below 10%.
Causing the bad major cause of partial heat treatment effect is the residual thermal stress that the partial heat treatment process itself is brought.In the partial heat treatment process, the thermal expansion that high-temperature area produces is subjected to the strong constraint of cold metal on every side, can not freely expand; Temperature spread between high-temperature area and the normal temperature zone also can be brought very big thermograde simultaneously, and everything all can cause thermal stresses.Thermal stresses generally can meet or exceed the yield strength of the material under the corresponding temperature under the high temperature, thereby produces plastix strain; In process of cooling, these plastix strains can not recover fully, thereby cause residual thermal stress and residual set.
Summary of the invention
The present invention is the purpose that solves spherical vessel partial heat treatment residual thermal stress problem in order to overcome the problem that above technology exists, a kind of local heat treatment residual heat stress control method of spherical vessel to be provided, reaching, and residual thermal stress is controlled on the aspiration level.
To achieve these goals, the technical solution used in the present invention is: a kind of local heat treatment residual heat stress control method of spherical vessel, it is characterized in that, at first according to the required area that is subject to processing the zone of volume, wall thickness and the partial heat treatment of spherical vessel, according to different residual thermal stress aspiration level, calculate heating region arc length radius, when the residual thermal stress of expectation be material normal temperature yield strength 40%, 30%, 20%, 10%, 5%, 0% the time, corresponding heating region arc length radius calculation formula is respectively
R is the spherical vessel inside radius, t is the spherical vessel wall thickness, calculate the pairing heating region arc length of intermediate stress level radius by linear interpolation, when the arc length radius that needs thermal treatment zone surpass heating region arc length radius 50% the time, should enlarge heating region arc length radius to the arc length equivalent that the major general exceed part; Selected heating appliances is placed on is subject to processing the zone, heat, adopt unilateral heating or two-sided heating, when adopting inboard unilateral heating, corresponding outer surface should be provided with thermal insulation layer, when adopting outside unilateral heating, corresponding inner surface should be provided with thermal insulation layer, but no matter unilateral heating still is two-sided heating, and heating appliances and air contacting surface all should be reliably adiabatic, and heating appliances is infrared ray heating plate, track type electric heating panel; Hot face is circular, and the zone that is subject to processing should be positioned at the hot face center; Should control heat-up rate in the heat-processed, make to be not more than 150 ℃/h; Reach thermostat temperature and handle by predetermined constant temperature time constant temperature after cool off; Speed of cooling should be controlled at heat-up rate 50% in, be cooled to 300 ℃ according to speed of cooling after, thermal insulation layer is removed, thermal treatment finishes.
Above-mentioned heating appliances is infrared ray heating plate, track type electric heating panel or flame heating.
Above-mentioned thermal insulation layer thickness should be not less than 100mm.
Beneficial effect of the present invention, solved the spherical vessel partial heat treatment residual thermal stress control problem of long-term puzzlement industry, can be according to different needs, the residual thermal stress that the spherical vessel partial heat treatment is caused be controlled at from yielding stress 40% to approaching zero level, thereby avoid potential safety hazards such as the stress corrosion crack that brings thus and brittle rupture, increase the main equipment safe reliability of operation continuously, and operational safety is convenient.
Embodiment
Below in conjunction with embodiment the present invention is described in further detail: a kind of local heat treatment residual heat stress control method of spherical vessel, at first according to the required area that is subject to processing the zone of spherical vessel volume, wall thickness and partial heat treatment, calculate the arc length radius of circular heating region, selected heating appliances is placed on is subject to processing the zone, heat.Can adopt unilateral heating or two-sided heating.When adopting inboard unilateral heating, corresponding outer surface should be provided with thermal insulation layer; When adopting outside unilateral heating, corresponding inner surface should be provided with thermal insulation layer.But no matter unilateral heating still is two-sided heating, and heating appliances and air contacting surface all should be reliably adiabatic.Hot face is circular, and the zone that is subject to processing should be positioned at the hot face center.Should control heat-up rate in the heat-processed, make to be not more than 150 ℃/h.Reach thermostat temperature and handle by predetermined constant temperature time constant temperature after cool off; Speed of cooling should be controlled at heat-up rate 50% in, be cooled to 300 ℃ according to speed of cooling after, thermal insulation layer is removed, thermal treatment finishes.Above-mentioned heating appliances comprises infrared ray heating plate, track type electric heating panel or flame heating.Above-mentioned thermal insulation layer thickness should be not less than 100mm.
The hot face of spherical vessel partial heat treatment should be circle.The zone that is subject to processing comprises that repair welding zone and heat affected zone thereof should be positioned at the center of hot face.Heating appliances comprises far-infrared heating plate, track type electric heating panel or flame heating, and heating appliances should be positioned at the homonymy, the outside or the inside and outside both sides that are subject to processing the zone and heat simultaneously.According to different residual thermal stress aspiration level, as follows with the heating region arc length radium computing method that the bus arc length is represented:
The applicable elements of aforementioned calculation method:
(1) thermostat temperature and constant temperature time should meet the regulation of concerned countries standard and technical specification of security.
When (2) adopting inboard unilateral heating, corresponding outer surface is thermal insulation reliably; When adopting outside unilateral heating, corresponding inner surface should be reliably adiabatic.Unilateral heating and two-sided heating all allow, but heating appliances and air contacting surface should be reliably adiabatic.
(3) exceed outside the circular heating region, annular adiabatic zone should be set, with the detrimentally affect that prevents that excessive thermograde from bringing.The width of annular adiabatic zone should be not less than 50% of heating region arc length radius.The annular adiabatic zone can be provided with circular adiabatic zone is unified.Thermal insulation layer thickness should be not less than 100mm.
(4) heat-up rate should be not more than 150 ℃/h, speed of cooling should be controlled at heat-up rate 50% in.
(5) when the arc length radius that needs thermal treatment zone surpass heating region arc length radius 50% the time, should enlarge heating region arc length radius to the arc length equivalent that the major general exceed part.
(6) should respectively two points for measuring temperature be set at least in the inboard that needs thermal treatment zone and the outside, centering and thermal treatment zone outer rim are as the feedback parameter of adjusting the heat input.But when thermal treatment zone is big, should set up point for measuring temperature in the thermal treatment zone outer rim.
If can not determine the residual stress level of expectation, should be according to 10% yielding stress Standard Selection heating region arc length radius.
When the heat treated zone of needs surpass heating region 50% the time (by arc length), should enlarge the heating region radius to the arc length equivalent that the major general exceed part.
The present invention adopts bigger heating and adiabatic area, and the thermal treatment zone speed of cooling can obviously slow down along with the reduction of metal temperature.In order to increase work efficiency, when the thermal treatment zone temperature drops to below 300 ℃, thermal insulation layer can be removed, to shorten man-hour.
The invention will be further described below by specific embodiment.
To a 1000m
3(inside radius R is 6204mm), wall thickness t are the spherical vessel of 40mm, if there is the long repair welding weld seam of 120mm, then the thermal treatment zone diameter is 120+40 * 2=200mm.The spherical vessel material is 16MnR, and the normal temperature yield strength is 307MPa, and with 40% (being 122.8MPa) of the yield strength expected value as the average residual thermal stress of thermal treatment zone, then heating region half arc length is
Owing to need heat treated regional arc length radius (100mm) less than 50% of heating half arc length, therefore do not need to increase hot face.The circular shape heater tool is placed inner surface, getting annular adiabatic zone width and be 1000mm, thermostat temperature and be 600 ℃, constant temperature time is that 2h carries out partial heat treatment, in the heat treatment process rate of heating is controlled at 100 ℃/h, speed of cooling is controlled at 50 ℃/h, the thermal treatment zone internal surface residual thermal stress that obtains is 123.4MPa, as seen very near expected value (122.8MPa).At this moment, thermal treatment zone outside surface residual thermal stress is 87.9MPa.