Method of making spheroidal bottoms in pressure vessels

FIELD: mechanical engineering; pressure vessels.

SUBSTANCE: according to proposed method, spheroidal bottom is made of sheet, thickness of 0.5-0.6 of designed thickness for initial elliptical bottom and is subjected to deformation at higher process upsetting pressure of 1.3-1.5 of designed value.

EFFECT: facilitated and reduced cost of manufacture.

2 cl, 1 dwg

 

The invention relates to the field of southstreet and can be used in the manufacture of boilers, tanks, tanks for the storage of gases or liquids in the chemical and petrochemical engineering in the manufacture of vessels with convex bottoms.

A known method of manufacturing spherical bottoms by stamping from flat blanks using the matrix in the form of a ring and punch with a spherical head [1]. The existing technology of punching thinner bottoms spherical shape necessitates a costly punches and due to the large extraction is labour intensive and unsustainable - is accompanied by the appearance of bumps on the cylindrical flared.

The modern rules of calculation of pressure vessels [2] the calculation of the permissible pressure [p] for elliptic bottoms is calculated by the formula

and the thickness of the bottom is determined by the formula

where H is the height of the bottom (or the semiminor axis of the ellipse in cross-section passing through the axis of rotation), r is the inner radius of the bottom at the junction of it with the cylinder, ϕ - weld factor, [σ] - allowable stress for the material of the bottom.

Formula (1) is an approximate expression of extreme pressure for a sphere with inner radius R

which is the place of ultimate strength σ insubstituted allowable stress [σ].

Formula (3) is used to estimate the ultimate strength of the elliptic bottoms on the assumption that the shape of the elliptical bottoms in the process of loading up to fracture does not change and the destruction occurs in the weakest place in the top of the ellipsoid radius of curvature in thisplace defined by the formula. Formula (3) are valid for elliptical heads, made of fragile materials. If the bottom is made of plastic material (e.g. steel), then in the process of loading up to fracture the bottom shape is changed, and the radius of curvature at the vertex of the bottom reduced, and thus the strength of the bottom increases.

As shown by experimental studies [3], for steel bottoms of the formula(1), (2), (3) unsuitable even for rough engineering estimates of ultimate strength elliptical heads. In the process of plastic deformation of the convex bottom gets meridional εzand the ring εt0permanent deformation and takes the form of a spherical segment, the rupture of which is determined by the formula

where the radius of the inner surface of the spherical segment R is equal to

r is the inner radius of the cylinder, which is Edinaya the bottom,

εt0- circular deformation of the bottom at the junction of it with the cylinder,

ϕR- the angle of a spherical segment, which is determined from the equation

Then the formula for the pressure of the destruction of the spherical segment takes the form:

Experimental studies to the destruction of the steel convex bottoms and calculations by the formula (7) shows that the actual pressure of the destruction of the convex bottoms of 70...80% higher than that calculated by the formula (3). Thus, the bottom can produce 1.7...1.8 times thinner than the existing standards [2], using the tooling for punching standard elliptic bottoms with the ratio H/r=0.5 in.

The proposed method of manufacturing spheroidal bottoms produced from standard elliptic bottoms with the ratio of height to radius H/r=0.5 of the hydraulic method, in which the elliptical plate is made of sheet thickness 0,5...0,6 calculated from the original elliptic bottoms by the formula (2) of the regulations [2] and pressed at a temperature of 60...80°With a process pressure of 1.3...1.5 calculated.

For the implementation of the proposed method standard elliptic plate with the ratio H/r=0.5 and a thickness of 0,5...0,6 calculated from the formula (2) is welded to the cylinder. the donkey construction of the shell of the vessel it must be supplied pilot pressure p CRequal to [3]

where [σ]20and [σ]t- allowable voltage (at 20°and at the operating temperature of the vessel respectively.

Proposed primary process pressure equal to

pCR=(...1,5 1,3)p

so that during the further operation of this pressure vessel was not repeated. According to the calculations of the stress state of the bottom and experimental studies (see drawing), while the pressure in several places meridional bending moments, which moves the entire wall thickness of the bottom for the yield strength (the so-called plastic hinges), which result in changes to the shape of the bottom. The drawing shows a plot of bending moments in elliptical bottom and locations of plastic hinges. The bottom turns into a spherical segment with a new radius of curvature at which the voltage from the design pressure does not exceed the permissible value. After changing the shape of the bottom of it can be made the necessary holes and glands.

The plot shows that at the junction of the elliptical plate with a thicker cylinder bending moment occurs the opposite sign. To reduce unwanted Flexural stresses at this location is proposed to perform cilindric the massive flared variable thickness with respect to the difference of the thickness to the length of the flange is not greater than 0.25.

To the deformation of the bottom has not led to brittle fracture, pressure testing should be carried out at elevated temperature (60...80°C), which provides the plastic deformation of the steel.

Literature

1. Okhrimenko AM Technology forging and stamping production. M., 1976.

2. GOST 14-249 "Vessels and apparatus. Norms and methods of strength calculation". The publishing house of standards, 1989.

3. Mordina G.M., Pimshtein p. g Strength elliptical bottom when loading internal pressure // XXIII Russian school of science and technology. Short communications - Yekaterinburg, 2003. - P.123-125.

1. A method of manufacturing spheroidal bottoms in pressure vessels, including stamping standard bottoms elliptical weld plate to the cylinder and the molding at a temperature of 60÷80°C, characterized in that, in order to obtain a given shape of the bottom of it is made of sheet thickness of 0.5÷0,6 calculated from the original elliptical bottom, and the pressure of technological crimp is 1.3÷1.5 km from the settlement.

2. The method according to claim 1, characterized in that, to reduce unwanted stress, flanging is of variable thickness with respect to the difference of the thickness to the length of the flange is not greater than 0.25.



 

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