Pipe Support

Welcome to Presentation on PIPE SUPPORT SYSTEMS & PIPING FLEXIBILITY (03-Feb-2005)

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Program Objectives 1.

To create a sense of appreciation for compliance of best engineering practices , and improve understanding of piping through preliminary knowledge of Pipe supports.

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To enable faster & better interpretation of engineering deliverables by working knowledge of these Pipe supports .

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To enable maintenance engineers to take preventive action case of exceptions.

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INDEX

PART-I Overview. PART-II Support Basics. PART-III Support Classification. PART-IV Support Detailing. PART-V Support Design. PART-VI Line Designation PART-VII Piping Flexibility PART-VIII Sample Drawings .

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OVERVIEW 9/19/2006

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THE CODE ASME B 31.3 SPECIFIES UNDER CLAUSE 321.1.1, THE OBJECTIVE OF THE SUPPORT DESIGN AS PREVENTION OF

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Piping stress in excess of those permitted in the code. Leakage at joints due to misaligned flanges. Excessive thrust and moments on connected equipment (such as pumps and turbines). Excessive stresses in the supporting (or restraining) elements.

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Resonance with imposed fluid induced vibrations Excessive interference with thermal expansion and contraction in a piping system, which is otherwise adequately flexible.(No unwanted rigidity). Unintentional disengagement of piping from its supports. Excessive piping sag in systems requiring drainage slope.

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PIPE SUPPORTS STANDARDS

1. ANSI31.1 &31.3 ie Power Piping & Process Piping 2. *MSS –SP 58 Pipe Hangers and Support : Materials, Design & Manufacturers 3. *MSS –SP 69 Pipe Hangers and Support : Selection & Application. 4. *MSS –SP 77 Guidelines for Pipe Support Contractual Relationships. 5. *MSS –SP 89 Pipe Hangers and Supports: Fabrication & Installation Practises. 6. MSS –SP 90 Guidelines on Terminology of Pipe Hangers & Supports. * These are advisory standards recommending standard practices.

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SUPPORT OR SUPPORTING ELEMENTS The term “supports” or “supporting elements” encompasses the entire range of various methods of carrying the weight of pipeline and the contents. It therefore includes “hangers” which generally carry the weight from above, with the supporting members being mainly in tension. Likewise, it includes “supports” which on occasion are delineated as those which carry weight from below, with supporting member being in compression. Pipe supports refer to the physical structural elements such as pre- engineered structural steel along with suitable springs, snubbers, fixed on pipes to reduce or nullify the forces created in piping systems due to self weight, thermal expansion or contraction, shock load, etc.

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Basic Terminology

•Pipe : Pressure tight cylinder to convey fluid/fluid pressure •Pipe Support Elements: Transmit the load from pipe to structures& /or pressure equipment Ex. Spring Hangers, Guides, Hangers. These are called Fixtures. Attachment like clips, clamps, strips etc. are called Structural Attachments.

•Piping Components: Joining/Assembling Mechanical elements for pressure tight piping etc. like Flanges, Gaskets, Valves, Expansion Joints, Hoses, Traps Strainers etc.

•Piping: Assemblies of piping components used to convey, distribute, mix etc. flows. Also includes piping elements.

•Piping Elements: Any material or work required to plan & install piping system is called piping elements. Specs, Materials, components, supports inspection etc.

•Piping System : Interconnected piping subjected to same set or varying sets of Design conditions. 9/19/2006

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Continued….. Hot load / Hot setting / Operating load The weight that the spring has to support while the pipe line system is in operation. This is also called Operating load. Cold load / Cold setting / Installed load The weight that the spring has to support while the pipe line system is NOT in operation. This is also called pre-set load. Travel stops Limit the spring travel at the top and bottom to a small percentage beyond the specified range. In addition, they prevent the spring form moving while the spring is not in operation (in pre-set mode) or in hydrostatic testing phase. Travel Compression or expansion of spring in “mm” from Hot to Cold or vice versa load variation. 9/19/2006

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Elements Of Pipe Support

1.

Fixtures: a. Hanger Rods b. Spring hangers c. Turn Buckles d. Chains e. Anchors f. Brackets g. Guides h. Saddles

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Structural Attachments: a. Clips b. Lugs c. U-bolts d. Straps

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Classification of Pipe Supports 1. 2. 3. 4.

Rigid or Weight Supports (Rod Hangers, Sliding supports, VS & CS Supports) Rigid Restraints & Anchors (Supplementary Steel or Structural Members ) Snubbers (Hydraulic & Mechanical ) Sway Braces

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Rigid Type Supports (Weight supports)

All sliding type supports: Bare, Clamped, Shoe, Dummy supports, bracket supports, etc. (supported from bottom). In this the supports members are in compression.

Hangers rods (without spring): Will be supported from top. (Designed on the basis of max. weight carrying conditions, including Hydro test). In this the supports are in tension.

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SHOE

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SADLE

CLAMP SHOE

BASE SUPPT

BASE ADJ.SPT

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BASE ELL SPT

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BASE ADJ SPT

DUMMY SPT

DUMMY SPT SHOE

VERT DUMMY

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ADJ. ELL. SPT

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ADJ. SPT.

ADJ.GUIDE

ADJ. GUIDE

SPT. NO WELD

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TRUNNION

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ELL.SPT.

SUPPORT

SUPPORT

CLAMP ELL.SPT

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ROD HANGER

THE

ROD

HANGERS

ARE

USED

FOR

NON

CRITICAL

SUPPORTS.

DIFFERENNT ATTACHMENTS LIKE EYE-NUTS,TURNBUCKLES,RODS HEX NUTS & BOLT CLAMPS ARE USED IN CONJUNCTION WITH HANGER RODS. TURNBUCKLES ARE FOR ADJUSTMENT IN THE SUSPENDED LENGTH FROM THE PIPE.

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ROD HANGERS

Offset Limitation of rod hangers a)

Pipe With Movement In Axial Direction

b)

Cold Pipe Positioning

– 1) Offset,Cold -- 2) Operating Position Hot Permissible horizontal movement not to exceed +4° for Rod hangers . 9/19/2006

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Anchors & Guides (Restraint Type) Anchors & Guides are provided to restrict movement of pipe in any one or all 6 freedom of movements. 1. They are provided to restrain, direct or absorb piping movements. 2. Their design takes into account forces/moments at these elements caused by internal pressure and thermal expansion/contraction. Supplementary Steel

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To attach the pipe with various type of supports mentioned above we need to tie it with the existing structure. To achieve this we either weld structural members to the supporting elements or supporting brackets on to the existing structure.

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PIPE SUPPORT MATERIAL FOR COLD SERVICES 1. Natural seasoned wood – IS 3629 Gr.I •

Along the grain cutting & across the grain loading

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Timber group A

1. HDPUF – Compressive Strength 70000 Kpa OR 70 KG per cm 2 •

Loyde grade 320 – 82000 KPa - Standard

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Loyde grade 250 – 49000 KPa - Standard

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Loyde grade 300 – 70000 KPa – (IPCL Customized) 9/19/2006

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Variable & Constant Supports (Flexible Supports) Variable Spring Supports: Variable spring supports are so called because they provide variable supporting forces as the pipe moves vertically due to contraction or elongation. Maximum variation in load is 25%. Constant Spring Supports: Constant spring supports are used where thermal movements are too large (over 2 inches & max 6% load variation is allowed). Such spring supports are used to restrict the loads created in piping systems on to critical equipment nozzles. NOTE: (In Spring Supports springs are not designed for Hydrotest loads, however supports members are designed to take hydro-test loads.) 9/19/2006

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Spring Hanger in four different load conditions

a) Unloaded Position 9/19/2006

b) Loaded in Hot position

c) Pipe moves down from cold to hot position

d) Pipe moves up from cold to hot position 22

TYPES OF VARIABLE –SPRING HANGERS

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Variable Spring Supports (Flexible Supports)

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SELECTION OF FLEXIBLE SUPPORTS CONSTANT SPRING :

Constant spring hangers are selected where absolutely necessary, when the percentage variation of load from cold to hot should be less than ± 6% for critical pipelines, which give the lowest %, load variation. The geometry & kinematics of these constant spring hangers is such that theoretically and constant supporting force can be achieved throughout its full range of expansion and contract.

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Constant Effort Spring support

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CONSTANT-SPRING SUPPORT

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Constant Spring Supports (Flexible Supports)

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VARIABLE SPRING Variable spring hangers are recommended for general use on non-critical piping systems & where constant supports are not required. The inherent characteristic of a variable spring is such that its supportings force varies with spring deflection and spring scale. The vertical expansion of piping causes a corrresponding compression or extension of spring & causes a change in the actual supporting force is equal to the product of amount of vertical expansion & the spring scale. 9/19/2006

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Comparison of variable support & constant support Springs

Particular

Variable Spring Support

Constant Spring Support

Design

Simple design with Helical spring

Sophisticated design with Spring & Bell Crank Lever

Application

Non critical applications – Ex. Heat Exchangers, Vessel, ordinary piping etc.

Critical applications – Ex. Steam piping near steam turbines , Steam Headers ,Boilers etc.

Movement

Applicable for Low thermal movements (upto 50 mm)

Applicable for large thermal movements (above 50 mm)

Space

Less space for installation

Large space for installation

Cost

Low cost

High cost

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Formulas And Calculations

Upward movement

- If Cold load is greater than Hot load

Downward movement

- If Hot load is greater than Cold load

Movement = (Cold load - Hot load) / Spring rate. If result > 0 then movement direction is up. Otherwise, it's down. Variability (% load change)

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= ((Movement x Spring rate) / Hot load) x 100

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SNUBBERS Rigid restraints are usually necessary when the pipe is strong to survive loads such as earthquake or high winds or other dynamic loads such as fluid hammer. But when these restraints are used in high temperature piping at some location it may develop elevated stress levels. In these cases snubbers are used.

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SNUBBER ASSEMBLY

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Mechanical Snubber

a) Photograph b) Schematic 9/19/2006

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Hydraulic Snubber

a) Schematic b) Photograph 9/19/2006

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SWAY BRACES Sway braces are used to limit the effect of pipe vibration. These are little more than variable springs acting in horizontal plane. When sway brace is installed, the spring preload is adjusted to be zero when pipe is in the operating position. Sway braces, like variable springs, do add some expansion stresses in the pipe.

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SWAY BRACES

A) Vibration Control & Sway Brace. B) Cutaway Section C) Deflection of Spring when Thrust Exceeds Pre-compression D) Tension Causes deflection of Spring in Opposite Direction

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LOAD COMBINATIONS

Pipe supports must be designed to withstand any combination of loading which is postulated to occur simultaneously. Normal operating loads are either deadweight or deadweight plus thermal. These loads may be combined with occasional loads, as required by the design criteria of the specific project. Under certain conditions, capacities of materials may be increased for occasional loads. E.g. is the concept of service level instituted by ASME Boiler & Pressure Vessel Code, Section III. A typical spec for design load combination is as follows:-

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Load Cases Normal

I Deadweight II Deadweight + Thermal

Upset

I Normal + relief valve discharge II Normal + earthquake(DBE) +relief valve discharge. III Normal + water hammer

Emergency

Normal + earthquake (DBE)+ Relief valve discharge.

Faulted

Normal + earthquake (DBE) + pipe rupture.

These loads may be added either algebraically to arrive at realistic values or absolutely for added conservatism, according to the design criteria requirements.

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MAXIMUM SPAN BETWEEN TWO SUPPORTS As per ASME B31.1 Table 12.5 adopted from MSS-SP-69

Pipe (NB)

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Suggested Maximum Span Water mtr. (ft)

Air /Steam mtr. (ft)

1

2.1 (7)

2.7 (9)

2

3.0 (10)

4.0 (13)

3

3.7 (12)

4.6 (15)

4

4.3 (14)

5.2 (17)

6

5.2 (17)

6.4 (21)

8

5.8 (19)

7.3 (24)

12

7.0 (23)

9.1 (30)

16

8.2 (27)

10.7 (35)

20

9.1 (30)

11.9 (39)

24

9.8 (32)

12.8 (42)

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GUIDELINES FOR LOCATION OF SUPPORTS

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Support should be located at near as possible to concentrated loads as valves, flanges etc. To keep the bending stress to the minimum. When changes of direction in a horizontal plane occur, it is suggested that the spacing be limited to 75% of the tabulated values to promote stability and reduce eccentric loadings.

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The standard span does not apply to vertical run pipes (risers) since no moment and no stress will develop due to gravity load in the riser. The support should be located on the upper half of a riser to prevent instability in overturning of pipe under its own weight. Support location should be selected near the existing building steel to minimize the use of supplementary steel. 9/19/2006

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SPECS FOR ORDER o

o o o

o o o

o o

The exact hot or operating load required to be supported during the working condition. Hydrostatic test load. The total travel. The direction of travel either upwards or downwards from the erected position. The set pin locking position (top, middle, bottom or as required). The basic model. Requirement of bottom accessory components such as rods, clamps etc. Any hazardous environmental conditions. Any special finish on the body such as galvanizing etc.

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Phenomenon in Piping Flexibility CREEP RUPTURE STRENGHT Time dependant stress is usually related to the “Creep Rupture Strength” at high temperature. At temperature above 1/3 of the melting point most metals will exhibit creep in standard tensile test. If the load is kept constant the specimen will continue to deform and subsequently fail. Hence considering this creep, the allowable stresses are 62.5% of the yield stress. Hence taking a conservative estimate the limit of the bending stress at which plastic flow starts is 1.6 times the allowable cold or hot stress. FATIGUE ON PIPING ARC Markl investigated the phenomenon of fatigue in piping. He observed that the fatigue failure occurred not in the middle of his test spans, but in the vicinity of fittings and that also at a lower stress than that for pipes. This lead to a factor called “Stress Intensification Factor”. 9/19/2006

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Piping Support Design Tips 1.

2.

3.

4.

5.

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Since most piping systems are not made strictly of straight horizontal runs, the standard support spacing may not be applied uniformly throughout. Locations of supports should consider the following guidelines. Pipe supports should be located as near as possible to concentrated weights such as valves, flanges, etc. From a pipe stress point of view, the best location for support attachment is directly on the equipment. When changes of direction in a horizontal plane occur between the pipe and associated supports, such as with pipe elbows, it is suggested that the spacing be limited to three-fourths of the standard span shown in table. The standard span does not apply to vertical runs of pipe (risers) since no moment (and therefore no stress, as defined by the piping codes) will develop owing to gravity loads in riser. Support locations should be selected near existing building steel to maximize ease of design & construction and to minimize the supplemental structural materials used to transmit the pipe loading back to the building structure.

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Key Maintenance Tips •

Adequately designed piping and support systems are absolutely critical & important.

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Major failure of supports can be catastrophic.

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It becomes absolutely necessary for maintenance engineers to be very vigilant towards critical support systems and check for following common piping support problems : Shoe not resting on the sleepers. Shoe twisted. Support weathered away. Trunnion / Dummy bent on vertical lines. Structural members bent near loops. LPDs embedded in soil thus turning it into an anchor support.

1. 2. 3. 4. 5. 6.

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Key Maintenance Tips Continued…. • • • • • • • • •

Wooden blocks placed under elbow dummies weathered off. Guide plates in guided supports missing. Pipe stops in axial restraint broken / bent. Blocks attached to these pipe stops weathered off. Variable Spring Supports Corroded. Variable Spring Supports locks not removed. Due to displacement Variable spring supports not operational. Pipe is corroded where it is directly resting on sleeper rod. Line is not supported adequately, high cantilever.

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PIPING CLASS CODING „ „

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„

„

3-Character System : X - X - XXXX - XXX - XX 1st Slot/Character : Line size in inches 2ND Slot/Character : P-Process ; CWS-Cooling Water Supply ;CWR-CW Return; N2-Nitrogen; H2-Hydrogen; AS-Service Air; AI-Instrument Air; AP-Plant Air; FW-Fire Water; DMW-DM Water, etc. 3rd Slot/Character : 4 Digit Line Sr.No. 4th Slot/Character : Piping Class a) First Character specifying : A-150# B-300# D-600 # E-900 # F-1500 # G-2500 # b) Middle No. specifying variants. (1 2 3 4 5 7 8 9 10 13 19 20) c) Third Character specifying : A-CS, B-CS MOLY, C D E H K M N S-PVC, T YMSRL Z-HDPE (Ex: A1A, A2A A3A, A4A, B1A, B2A.., B1K, B2K, D1A,D2A, D5A, F2A, F2D, G2E)

„

5th Slot/Character : Insulation Type IH, IC, IS, ET

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Piping Flexibility An Introduction

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Expansion Loads Piping system which is too well restrained will not be able to expand and large forces will develop at the points of lockup, causing large stresses to develop in the pipe. The ideal restraint conditions for thermal considerations is a total lack of restraint. Since this is not feasible, given other loads, some forces due to expansion will develop on restraints even in the most optimally supported system. Hence it is necessary to determine piping thermal movements for use in spring hanger selection and design of clearances in restraints.

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THERMAL EXPANSION OF PIPING SYSTEM

(a) Loop without directed thermal growth 9/19/2006

(b) Loop with directed thermal movement

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a.Poor Service/Piping Distortion.

b.Proper Service/Piping alignment & limited stresses through PSA . c.Poor Service/ Unnecessary looping etc . a.Good but Costly due to heavy design . 9/19/2006

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Calculation of Pipe Expansion A pipe will expand when heated up and contract when cooled. This can be expressed through the expansion formula.

The temperature expansion of pipes depends on the start and final temperature and the thermal coefficient of expansion of the piping material. The general expansion formula can be expressed as: dl = ∝ x Lo x dt

where: dl = expansion (inches) Lo = length of pipe (inch) dt = temperature difference (oF)

∝

= linear expansion coefficient (inch/inchoF) (available in 31.1,

31.3,etc) Example: Thermal expansion for 1 meter Carbon steel pipe at 100ºC. dl = 6.38/10

x 1000 x (212 – 93) = 0.76 mm/meter

For Carbon Steel ∝ = linear expansion coefficient (inch/inchoF) = 6.38/10 Remember Expansion in SS pipe will be approx. 30- 50% more than in a carbon steel pipe. 9/19/2006

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CTE OF PIPING MATERIALS (Total linear Thermal Expansion in / 100’) c

-300 °F

-100 °F

- 25 °F

70 °F (ambient)

200 °F

400 °F

A 106 (CS)

- 2.24

- 1.15

-0.32

0

0.99

2.70

A 312 – 304 (SS)

- 3.63

- 1.75

-0.46

0

1.46

3.80

CTE (At 1000F) CS

6.13

micro in./In./ °F

SS

9.16

micro in./In./ °F

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PIPE UNDER STRESS There are two types of loads which put a pipe under stress: 1.

Primary Loads: These loads are typical loads such as internal pressure, external pressure, gravitational forces like the weight of pipe and fluid. These loads are generally called as sustained loads. Failure of the pipe due to any of the mentioned loads are called as catastrophic failures.

2.

Secondary Loads: Just as primary loads have origin in some force, secondary loads are caused by displacement of some kind. e.g the pipe may be under load if the tank nozzle moves up or down. A pipe subjected to a cycle of hot and cold fluid similarly undergoes cyclic loads and deformation.

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PSA OBJECTIVE Pipe Stress analysis is carried out to ensure safety against failure of the PIPING SYSTEM by verifying the structural integrity against the loading conditions, both external and internal during the life time of the system in the plant. Hence the objectives can be stated as : 1. Ensure that the stresses in the piping components in the system are within the allowable limits. 2. Solve dynamic problems developed due to mechanical vibration, fluid hammer, pulsation, etc. 3. Solve the problems associated due to higher or lower temperatures. When piping is connected to strain sensitive equipment, the flexibility required to satisfy the acceptable limits of nozzle loading on the connected equipment overrides all other considerations. The piping systems are mainly classified into 3 main categories and then again sub-categories. The main categories are HOT Systems, COLD Systems and CRYOGENIC Systems. In this the hot and cryogenic lines must undergo FLEXIBILTY ANALYSIS. 9/19/2006

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• REQUIREMENT OF STRESS ANALYSIS No formal stress analysis is required if: • The piping system is duplicate of successfully operating installations or replacements. • Can be readily adjudged adequately by comparison with previously analysed systems. • Satisfy equation Specified in the clause 119.7.1(A3) / 319.4.1(c).

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BASIC INFORMATION

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A set of piping general (GAD) A Complete set of steel & structural drgs including the equipment foundation. A set of drgs showing the location of ventilating ducts, electrical trays, instrument trays etc. A set of piping spec and line list, which includes pipe sizes, M.O.C., thickness of insulation, operating temperatures etc. A copy of insulation spec. With densities. A copy of valve and specially list indicating weights. The movement of all critical equipment connections such as turbines, compressors, boilers etc.

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ON COLLECTION OF THE ABOVE DATA, THE STEPS IN WHICH THE PIPE STRESS ENGINEER WILL APPLY THIS BASICS TO DESIGN THE PIPING SUPPORT SYSTEM .

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The determation of support location. The determination of thermal movement of the piping at each support location. The calculation of load at each support location. The selection of load at each support location. The selection of type of support i.e. Anchor, Guide, Rest, Constant or Variable Spring etc. Checking physical interference of the support with structures, trays, ducts eqpts etc

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• Excessive distortion subject to creep under conditions of repeated thermal cycling. • Excessive heat flow, exposing supporting elements to temperature extremes outside their design limits.

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Support Drawing Samples

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Thank you 9/19/2006

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