Design of Marine hydraulic flange and connecting bolt
This paper discusses the key points and methods of marine hydraulic flange design, and provides a group of Marine hydraulic flange design examples.
There are three kinds of marine hydraulic flange standards: asian system represented by Japanese standard, European system represented by German standard and North American system represented by the United States. German standard and American standard varieties are more complete, but in the shipbuilding industry is far less than the use of Japanese standard. The conventional flange of JIS is more popular, while the hydraulic flange is not separate into a system, commonly used only 210 Kgf /cm2, 280 Kgf /cm2 and 350 Kgf /cm2 three specifications.
For a long time, high pressure marine hydraulic flange has few specifications, high price, long delivery time and other problems in the market. Considering that the number of hydraulic flanges required throughout the ship is not much. Some shipyards with machining ability often manufacture high-pressure hydraulic flanges by themselves. This paper mainly discusses the basic points of marine hydraulic flange design and gives a design example.
Marine flange design
There are many methods for marine flange design, such as bach method based on material mechanics, waters method based on elastic analysis by TY8100 method, and analysis method based on plastic limit load, etc. These methods are too cumbersome and complicated for engineering applications. Based on the JIS hydraulic flange standard, this paper explores a design method suitable for shipyards.
Key points of marine design
Marine flange as a connector, facing the big problem is sealing leakage – gasket leakage and pressure surface leakage. The former is mainly related to the gasket material, which requires us to consider the temperature, hydraulic oil characteristics (acid and alkali, etc.), the working mode of hydraulic power source (reciprocating pump or rotary pump, etc.), working pressure, hydraulic oil flow rate and so on to choose the appropriate gasket. There are many reasons for the latter, including insufficient flange stiffness, uneven flange surface, insufficient gasket stiffness, etc. Most of these are technical reasons, as long as the process is well controlled, the problem can be solved. Insufficient stiffness must be paid attention to at design time. Insufficient stiffness is prone to excessive warpage deformation, resulting in leakage. The simple way to improve stiffness is to increase thickness. The following provides a calculation method with flange thickness as the final value of the design, for your reference.
Design with marine flange thickness as final value
Marine flange connection of various forms, the hydraulic system for the method of orchid. Here, only the case of the O-ring seal embedded in the method blue is considered, as shown in Figure 1, from which the relevant parameters can be understood.
Fig.1 Method of embedding a sealed O-ring
To simplify the calculation, the following external forces are excluded:
- (1) the external force transmitted by the connecting piping systems;
- (2) thermal stress generated by internal high-temperature oil.
The stress of flange and bolt due to different thermal expansion difference.
The designed working pressure of A hydraulic system is 42.5 MPa, and the pipe diameter is 50 A.
The connecting flange and bolt of this system are designed by trial. The material is 45 steel.
Flange thickness calculation:
T take 37 mm, flange cover take the same thickness.
Note: For simplicity in this example, only the operating state is considered, not the preload state.
- M0: total external torque of marine flange;
- Md: HDHD, moment generated by internal pressure on inner diameter surface (N.mm);
- Mg: HGhG, torque generated by the difference between bolt compression force and internal pressure (N.m);
- MT: HTHT, torque generated by the difference between the total internal pressure and the internal pressure in the inner diameter surface force (N. Mm);
- HD: distance between bolt hole center and HD operation point;
- Hg: the distance from the center of the bolt hole to the point of operation of Hg;
- HT: Distance from bolt hole center to HT application point;
- C: The diameter of the circle with the radius from the center of the flange to the center of the bolt hole is 2 times the inner diameter;
- B: inside diameter of flange, take inside diameter of pipeline, 50 A;
- G: gasket diameter: 1.25 times of flange inner diameter;
- DG: outer diameter of gasket (DG-G is O ring in the marine flange contact area, generally take 1~2 mm);
- P: internal pressure, 42.5 MPa;
- N: number of bolts, take 4;
- Dh: bolt diameter, take 20;
- Sigma F is tensile strength at service temperature.
The diameter of the bolt is coarsened to 20 for checking:
- The value of dh is 27;
- Dh: bolt diameter;
- A: Effective cross-sectional area of bolts;
- H: Total internal pressure;
- σb: the tensile strength of the material;
- Finally, the bolt hole is 27mm and the flange thickness is 40mm.
Fig. 2 Finished marine flange
As a result, the marine flange thickness and bolt holes are less than the standard size of 42MPa flanges. Our factory has produced marine hydraulic flange according to this calculation for many times, and the effect is good without leakage. Fig. 2 shows the finished marine flange, and it is hoped to be beneficial to our shipyard by extension.
Author: PAN Deng, HE Lingfeng
Source: China Marine Flange Manufacturer – Yaang Pipe Industry (www.steeljrv.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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Please notice that you might be interested in the other technical articles we’ve published:
-  Japanese Industrial Standards Committee JIS B2220 Flange Thickness Calculation Standard [S].2002
-  Li Xinhua Flanges Practical Manual [M]. China Standard Press,2006.4
- Mechanical Design Manual of Marine Editorial Committee Mechanical Design Manual [M]. China Machine Press,2005.3
-  Zhang Xu. Discussion on Flange Checking Method in Pressure Pipeline Design [J]. Petroleum & Chemical Equipment,2010,(8)