A general installation requirements
① gasket and flange sealing surface should be clean, without any impact on the performance of joint seals scratches, spots and other defects.
② washer OD should be smaller than the outer diameter of the flange sealing surfaces, gaskets diameter should be slightly larger than the pipe diameter, half the difference between the two inner gasket thickness 2 times to take in order to ensure pressed, the washer will not extend into the inner edge container or pipe, container or pipe to avoid affecting the flow of the fluid.
③ gasket preload should not exceed the design requirements, in order to avoid excessive compression gaskets lose resilience.
④ gasket compression, it is best to use a torque wrench. For large bolts and bolt, preferably using a hydraulic tightening device. Tightening torque should be based on the given gasket clamping force obtained by calculation, hydraulic oil pressure to tighten the size should be determined by calculation.
⑤ mounting pads, they should be the sequence of Figure 3-14 tighten the nut. It should not reach the design value winding once. Usually at least for 2 to 3 times to gasket stress distribution.
⑥ for flammable and explosive media pressure vessels and piping, gaskets facelift security tools should be used, so as to avoid tools and flange bolts with flange or collide, sparks, causing a fire or explosion.
⑦ If leaking pipes must be replaced or adjusted antihypertensive treatment after installing gaskets, non-pressure operation.
Second, special installation requirements
① mounted on the flange mating projection plane spiral wound gasket should be taken to ensure that seals the pipe concentric outer reinforcing Universal bolts commonly used surface contacts the inner circle to locate, not eccentrically mounted. Installing tongue and groove flange sealing surface of the basic type spiral wound gasket, attention should be consistent with the groove wall to keep the gap.
② mounting width narrower metal coated pad, should a gasket placed on the outside of the plate thickness, and then pressing the flange, so the coated filler gasket pressure after the metal shell interface (or ride buckle) expansion opened, damaged gasket.
③ When the flange temperature higher than 200 ℃, the flange and gasket sealing surfaces should be coated with sealant between to prevent high temperature gasket and flange sealing surface sintering, to repair and replace gaskets increase the trouble.
④ sealing surface is not flat, the surface can be coated with the sealing gasket sealant before installation. Sealants generally manganese dioxide, lead, graphite powder and survived linseed oil (drying) components. According to the sealing medium, temperature and pressure conditions choose the appropriate media type and brand of liquid sealant.
⑤ For installation octagonal metal ring gasket, when a metal ring gasket and flange seal groove machining is not ideal, it can be achieved by coordination study snug fit. For large diameter metal ring gasket, with research more difficult, in order to fill the tiny metal surface uneven, use sealant.
Third, the installation before the bolts, flanges and gaskets inspection
1 check for bolt and nut
① bolts and nuts of the material, type, size should be consistent with requirements of the drawings;
② Turn the nut on the bolt should be flexible, do not shake;
There should be bent bolt ③ phenomenon;
④ bolt threads are not allowed off phenomenon.
(2) the inspection of the flange
Should check the flange type meets the requirements, the sealing surface is smooth, with or without mechanical damage, radial scratches and corrosion.
3 check the gasket
① gasket material, type, size meet the requirements;
② gasket surfaces for mechanical damage, radial scratches, severe corrosion, damage and other defects inside and outside edge;
③ For oval and octagonal-shaped metal ring gasket should be checked before installation flange trapezoidal groove dimensions to meet the requirements, the tank is clean. Ring gasket contact surface can be painted in red lead oil to check the contact is good. Such as poor contact, should be ground.
Fourth, the quality of the pipe and flange mounting requirements
1 flatfish
Refers to the pipe and the flange is not perpendicular to different heart, flange faces are not parallel. Permissible deviation between the two flanges is: the use of non-metallic gaskets, should be less than 2mm; using metal - nonmetal combination of gaskets and metal gaskets should be less than 1mm.
2 wrong port
Refers to the vertical pipes and flanges, but the two flanges of different heart. Hole diameter of the bolt and the bolt diameter composite standard case, no other tool can freely penetrate the bolt bolt holes to pass.
3 mouth
Refers to the flange gap is too large. Allowed between two flanges mouth value (the value of pre-stretched tube was removed and the plate thickness shims or blind) as: pipe flange mouth should be less than 3mm; connected with the device over the flange should be less than 2mm.
4 wrong hole
Means concentric pipes and flanges, but the two flanges corresponds to the distance between bolt holes chord large deviations. Bolt circle radius tolerance of:
Bolt diameter ≤ 30mm, the tolerance of ± 0.5mm;
Bolt diameter> 30mm, the tolerance of ± 1.0mm;
Spacing between two adjacent bolts allowable deviation of ± 0.5mm.
Any of several chord distance between holes total deviation is:
DN ≤ 500 flanges, tolerance of ± 1.0mm;
DN600 ~ 1200 flanges, tolerance of ± 1.5mm
DN1300 ~ 1800 flanges, allowable deviation of ± 2mm.
V. The method of controlling the bolt fastening force
Mounting bolt flange connection, before the bolt according to recency, lubrication, material, etc. estimate the clamping force. If the tightening force is too small, then the gasket preload stress enough connection can not be achieved seal. If the tightening force is too large or the sealing surface of gasket often cause damage. For spiral wound gasket, such as tightening force is too large, due to excessive compression gaskets will lose elasticity; For metal corrugated gasket, such as tightening force is too large, sharp teeth will be flattened and lost tooth washer advantages. Therefore, the bolt tightening force to be controlled, the control bolt tightening force has the following three methods.
1 Use the special tool
Use of force, such as wrenches, torque wrenches and other special tools set, calculate and control the preload.
(2) measuring bolt elongation
Measuring bolt elongation calculated according to the following formula preload: δ = Wnl / Ed0
Where: Wn - each bolt preload;
      δ - bolt elongation;
      l - the distance between the two nut bearing surface;
      E - modulus of elasticity of the bolt material;
         d - diameter of the bolt rod section.
3 using the torsion angle method
Nuts and flange nuts after snapping, this time with the desired angle of rotation to control the preload.
     ψ = 3600 / P * δ
Where: ψ - the angle of rotation required;
       P - the distance bolt.
Six, high-voltage equipment fastening bolt
 Generally large cap high-voltage equipment, manhole flange bolt diameter coarse, workers hammering or previously used cranes, winches pull the long-handled wrench to tighten the bolts, labor-intensive, low efficiency, tightening force on the uneven, often resulting in inadequate or bolt force too large. Hydraulic tensioner bolt tightening pressure equipment is an ideal approach.
 By the high pressure pump hydraulic tensioners, hydraulic tensioners delivery tube and the first three parts. High pressure pump is generally hand pumps, hydraulic transfer tube pressure rubber hose. China has developed a maximum pressure of 150MPa hydraulic stretcher and put into small batch production [7].
 Figure 3-15 is a schematic structural view stretcher head. High pressure pump generates high pressure oil into the cylinder through the high pressure rubber hose to push the piston 2, on top of a nut and tighten bolts 9. Reaches a predetermined hydraulic pressure, with a small iron bar into the high-pressure side of the nut 6 hole will tighten them. The middle of the support tube 7 is opened 2-3 long holes, in order to ensure high iron insert can spin the nut over a certain angle. A pump can be equipped with a number of stretcher head, commonly used is 4.
The final hydraulic hydraulic tensioner bolt force can be calculated based on the total:
      p0 = ηW / Na
Where: p0 - the ultimate oil;
      η - Tighten coefficient;
      W - total bolt force;
      n - the number of bolts;
A - stretcher head piston effect of the total area.
    Tensioners tighten the coefficient η is the reciprocal of its mechanical efficiency, it is part of the length of the bolt is stretched and polished rod diameter ratio Ls / d0 relevant. Ls / d0> 15 ~ 20, η changes little and tends to a constant value. η generally take 1.3.
    Hydraulic stretching device easy to use. High pressure pump and tubing can be generic, just under high pressure bolt diameter matching a certain number of stretcher head can be.
Tighten the bolts must be repeated, general circulation 4 to 5 times.

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