Expansion & contraction

Transcription

1 Expansion & contraction All materials expand & contract with thermal change & pressure change. In case of piping systems, this dimension change can produce excessive stresses throughout the piping system and at fixed points such as vessels and rotating equipment, as well as within the pipe itself.

2 Expansion Joint Pipe expansion loop may add the required flexibility to a piping system if space permits. However the initial cost of the additional pipe, elbow & support must be considered for the pipe expansion loop system. In addition, increased continuous operating cost due to pressure drop may result the frictional resistance of the flowing media through additional pipe & elbow. In some cases, pipe diameter must be increased to compensate the losses due to pressure drop. Pipe Expansion Loop

3 Expansion Joint A practical & cost effective means of achieving piping system flexibility in a compact design is through the application of Expansion Joints. The most efficient piping system is the shortest and most directly routed system & expansion joints make it possible. Expansion joint provide an excellent solution for isolation of settlement, seismic deflection, mechanical vibration and sound attenuation transmission produced by rotating equipment.

4 Expansion Joint Metal bellows expansion joint consist of a flexible bellows element, appropriate end fitting such as flanges or butt weld ends to allow connection to the adjacent piping or equipment, and other accessory items that may be required for a particular service application.

5 Expansion Joint

6 Expansion Joint Bellows are manufactured from relatively thin walled tubing to form a corrugated cylinder. The corrugations, commonly referred to as Convolutions add the structural reinforcement necessary for the thin wall material to contains system pressure. The bellow designer selects the thickness and convolution geometry to produce a bellow design that approaches, and often exceeds the capacity of adjoining pipe to contain system pressure at a specific design temperature. Flexibility of the bellows is achieved through bending the convolution side walls, as well as flexing within their crest & root radii. In most cases, multiple convolutions are required to provide sufficient flexibility to accommodate the expected expansion and contraction of the piping system.

7 What metallic expansion Joint DO

8 Expansion Joint

9 Expansion Joint Axial movement is the change in dimensional length of the bellows from its free length in a direction parallel to its longitudinal axis. Compression is always expressed as negative ( ) and extension as positive (+). The units for axial spring rates displayed in N/mm.

10 Expansion Joint Lateral movement is the relative displacement of one end of the bellows to the other end in a direction perpendicular to its longitudinal axis (shear). Lateral movement can be imposed on a single bellows as depicted below but to a limited degree. A better solution is to incorporate two bellows in a universal arrangement as shown This results in greater offset movements and much lower offset forces. The units for lateral spring rates displayed in N/mm

11 Expansion Joint Angular movement is the rotational displacement of the longitudinal axis of the bellows toward a point of rotation. The convolutions at the inner most point are in compression ( ) while those furthest away are in extension (+). The angular capability of a bellows is most often used with a second bellows. The units for angular spring rates displayed in Nm/deg

12 Expansion Joint Torsional movement is the rotation about the axis through the centre of a bellows (twisting). Many expansion joint manufacturers DISCOURAGES ANY TORSIONAL ROTATION OF METAL BELLOWS EXPANSION JOINTS. Torsion destabilizes an expansion joint, reducing its ability to contain pressure and absorb movement. If torsion is present in a piping system, hinges, slotted hinges or gimbals are recommended to combat the torsion. Torsional spring rates are in Nm/deg and maximum torsional limits in degrees for computational modelling only. Piping software such as CAESAR II and COADE often require these spring rates for nodal input.

13 Pressure thrust

14 Pressure thrust

15 Single bellow expansion Joint

16 Single bellow expansion Joint The simplest type of expansion joint consists of a single Bellows element welded to end fittings, normally flange or pipe ends. The single bellows can absorb small amounts of axial, lateral and angular movement with ease, but adequate anchors and guides must be provided

17 Single bellow expansion Joint

18 Axial type bellow expansion Joint Unrestrained expansion joint must be used in anchored & guided systems which require anchors at each end of a pipe run that are sufficient to react to pressure thrust at the highest pressure anticipated. These fixed points (anchors) insure that the pipe grows (or contracts) & compressed (or extends) the expansion joint. The guides insure the motion is axial only.

19 Axial type bellow expansion Joint

20 Axial type bellow expansion Joint

21 Pipe anchor & Pipe support/guide Pipe anchor Pipe support/guide

22 Universal expansion joint

23 Universal expansion joint This expansion joint consists of two bellows connected by a centre spool piece with flange or pipe ends. The universal arrangement allows greater axial, lateral and angular movements than a Single Bellows Increasing the centre spool length produces increased movement capability. Like the single, adequate anchors and guides must be provided.

24 Externally pressurized expansion joint

25 Externally pressurized expansion joint Line pressure acts externally on the bellows by means of a Pressure chamber. This allows a greater number of convolutions to be used for large axial movements, without fear of bellows instability. Externally Pressurized Expansion Joints have the added benefit of self draining convolutions if standing media is a concern. Anchors and guides are an essential part of a good installation.

26 Single tied bellow expansion joint

27 Single tied bellow expansion joint The addition of tie rods to a Single Bellows Assembly adds design flexibility to a piping system. The tie rods are attached to the pipe or flange with lugs that carry the pressure thrust of the system, eliminating the need for main anchors. With the assembly tied, the ability to absorb axial growth is lost. Only lateral and angular movement can be absorbed with the tied expansion joint. The addition of tie rods does not eliminate the need for a well planned guide system for the adjacent piping.

28 Tied universal expansion joint

29 Tied universal expansion joint Similar in construction to a Universal Assembly except that tie rods absorb pressure thrust and limit movements to lateral offset and angulation. Large offset movements are possible in a Universal Assembly by increasing the distance between the two bellows

30 Tied universal expansion joint

31 Hinge expansion joint

32 Hinge expansion joint When a Hinged Expansion Joint is used, movement is limited to Angulation in one plane. Hinged Assemblies are normally used in sets of two or three to absorb large amounts of expansion in high pressure piping systems. Only low spring forces are transmitted to the equipment. The hinge hardware is designed to carry the pressure thrust of the system, and often times, used to combat torsional movement in a piping system. Slotted Hinged Expansion Joints are a variant of the standard Hinged Expansion Joints that allow axial and angular movement. Important note: Once a Slotted Hinge is introduced, torsion in the piping system is still resisted but the hinge no longer carries pressure thrust.

33 Hinge expansion joint

34 Gimbal expansion joint

35 Gimbal expansion joint The gimbal restraint is designed to absorb system pressure thrust And torsional twist while allowing angulation in any plane. Gimbal Assemblies, when used in pairs or with a Single Hinged unit, have the advantage of absorbing movements in multi planer piping systems. The gimbal works the same as an automobile's universal drive shaft.

36 Gimbal expansion joint

37 Pressure balanced elbow expansion joint

38 Pressure balanced elbow expansion joint These assemblies are used in applications where space limitations preclude the use of main anchors. Pressure thrust acting on the line bellows (bellows in the media flow) is equalized by the balancing bellows through a system of tie rods or linkages. The only forces transmitted to equipment are low spring forces created by the axial, lateral, or angular movements. An elbow must be present in the piping network to install this style of expansion joint.

39 Inline pressure balanced expansion joint

40 Inline pressure balanced expansion joint If an elbow is not present in a piping network and pressure thrust Must be absorbed by the expansion joint, an In Line Pressure Balanced expansion joint is the solution. An equalizing bellows with twice the effective area as the line bellows is tied in the expansion joint through a series of tie rods. The opposing pressure forces cancel each other leaving only the low spring forces generated from the bellows deflection.

41 Externally pressurized pressure balanced expansion joint If large amounts of axial movement in a system are needed and the expansion joint must absorb pressure thrust, an Externally Pressurized Pressure Balanced expansion joint is the solution. The opposing force balancing theory is similar to the In Line Pressure Balanced Assembly except the opposing forces are generated from pressure acting on the outside of the bellows

42 Pressure balanced expansion joint

43 Pipe Stress Analysis ± Some pipes are subjected to high pressure and high temperature. Also pipes carry the load of the flowing fluid. ± We need to check and confirm the pipe is not going to fail with these loading. ± This process of checking the stress developed in the piping due to various loading is called Pipe Stress Analysis/Flexibility analysis. ± In the process of Analysis we apply various postulated loading on the pipe and find out the stress resulted from these loading. ± Then we check with governing codes if those stresses generated are acceptable or not.

44 Pipe Stress Analysis ± We have to check support load & movement for various loading condition. ± We also have to check out the terminal point loading generated from pipe to the equipment connected to the pipe. This loading are to be within acceptable limits of the equipment suggested by the vendors. ± We also have to find out the pipe (expansion) and need to keep the movement of pipe within acceptable limits. ± Pipe Stress Analysis is an Interactive and Iterative process. Each step is checked ± If a check fails we have to go back, modify the layout and restart the analysis. ± There are many piping stress analysis software in the market to help us to design a correct piping design

45 Expansion Joint A design specification shall be prepared for each pipe expansion joint application. Prior to writing the pipe expansion joint design specification it is imperative that the system designer completely review the piping system layout, flowing medium, pressure, temperature, movements, and other items which may effect the performance of the pipe expansion joint. Particular attention shall be given to the following items. The piping system should be reviewed to determine the location and type of pipe expansion joint most suitable for the application. Both the EJMA (expansion joint manufacturer association) standards and most reliable pipe expansion joint manufacturers' catalogues provide numerous examples to assist the user in this effort. The availability of supporting structures for anchoring and guiding of the piping, and the direction and magnitude of thermal movements to be absorbed must be considered when selecting the type and location of the pipe expansion joint. Torsional rotation of the bellows should be avoided or special hardware should be incorporated into the design to limit the amount of torsional shear stress in the bellows.

46 Expansion Joint The bellows material shall be specified by the user and must be compatible with the flowing medium, the external environment and the operating temperature. Consideration shall be given to possible corrosion and erosion. The 300 Series stainless steels may be subject to chloride ion stress corrosion. High nickel alloys are subject to caustic induced stress corrosion. The presence of sulphur may also be detrimental to nickel alloys. The material chosen shall also be compatible with the environment surrounding the pipe expansion joint, water treatment and cleaning materials. In some cases, leaching of corrodents from insulating materials can be a source of corrosion. Internal sleeves shall be specified in all applications involving flow velocities which could induce resonant vibration in the bellows or cause erosion of the convolutions resulting in premature failure.

47 Expansion Joint The system design pressure and test pressure shall be specified realistically without adding arbitrary safety factors. Excess bellows material thickness required for unrealistic pressures will often produce an adverse effect on the bellows fatigue life or increase the number of convolutions required which may reduce the stability of the bellows. In the case of high temperature applications, it may not be possible to test the expansion joint to 1.5 times the equivalent cold pressure rating of the system. This results from the various materials employed in the construction of the pipe expansion joint, temperature gradient utilized in the design, pressure stability criteria, anchor strength, etc. The manufacturer must be consulted. The maximum, minimum and installation temperatures shall be accurately stated. Where the ambient temperature can vary significantly during pipeline construction, pre-positioning of the pipe expansion joint at installation may be required. The pipe expansion joint manufacturer shall be advised if the pipe expansion joint will be insulated. Insulation details shall be furnished to the manufacturer in order to properly design the component parts.

48 Expansion Joint.The movements which are to be absorbed by the pipe expansion joint shall include not only piping elongation or contraction, but also movement of attached vessels, anchors, etc. and the possibility of misalignment during installation. Unless included in the design requirements, misalignment of the pipe expansion joint must be avoided. Where movements are cyclic, the number of cycles expected shall be specified. Similar to pressure, the movements specified must be realistic. An excessive safety factor can often result in an expansion joint which is unnecessarily flexible; thus its stability under pressure is unnecessarily reduced If the flowing medium can pack or solidify, provisions shall be made to prevent entrapment or solidification of the material in the convolutions which could result in damage to the pipe expansion joint or pipeline. Internal sleeves are usually installed in the direction of flow. If the stagnant flow medium trapped behind the sleeve is undesirable, drain holes in the sleeve, purge connections, or packing shall be specified. Where backflow will be encountered, an extra-heavy sleeve shall be specified to prevent buckling of the sleeve and possible damage to the bellows.

49 Expansion Joint The predicted amplitude and frequency of external mechanical vibrations to be imposed on the bellows, such as those caused by reciprocating or pulsating machinery, shall be specified. A resonant condition in the bellows will result in a grossly reduced fatigue life and must be avoided. The pipe expansion joint designer will attempt to provide a non-resonating design; however, the ability to always assure non-resonance is impossible. Therefore, field modifications to the pipe expansion joint or other system components may be necessary The piping system drawings shall specify the location of all anchors, guides, supports and fixed points. Both the anchors and guides must be suitable for the highest pressures to be applied to the system. IN MOST CASES THE TEST PRESSURE WILL BE SIGNIFICANTLY HIGHER THAN THE SYSTEM OPERATING PRESSURE

50 Expansion Joint The system designer shall specify those special features which best accomplish personnel protection in his particular system. Piping systems containing high pressure and/or hazardous materials which are located in close proximity to personnel shall be provided with additional safety features which will protect such personnel in the event of a failure in the system.

51 Expansion Joint Extra-heavy covers which could serve to impede the effect of a jet flow produced by a failure; however, such covers will not prevent the escaping medium from expanding and filling the surroundings in which it is located.

52 Expansion Joint Limit rods designed for dynamic loading can be employed to restrain the longitudinal pressure

53 Expansion Joint A two-ply or two concentric bellows design may be employed with each ply or bellows designed to contain the full line pressure. The annular space between the plies or concentric bellows can be monitored continuously for leakage by means of suitable instrumentation. A change in pressure in the annulus could be used to detect bellows leakage.

54 Expansion Joint The system designer shall provide for the accessibility of components (anchors, expansion joints, guides, etc.) in the piping system for periodic inspection after initial start up.

55 Expansion Joint

56 Expansion Joint

57 Shipping bar Shipping Bars These are temporary attachments that "hold" the expansion joint at its correct installed length during shipping and installation. Angle iron or channel section is used and is always painted bright yellow. Shipping bars must never be removed until after the unit has been correctly welded or bolted into the piping system. Caution: Tie rods or limit rods are sometimes mistaken for shipping bars. NOTE: Great care must be taken when removing the shipping bars. If a welding or burning torch is used, ALWAYS protect the bellows element from burn splatter with a flame retardant cloth or other shielding material.

58 Expansion Joint

59 Expansion Joint

60 Anchor

61 Anchor

62 Pipe guide