flexibility analysis of high temperature piping system
TRANSCRIPT
Flexibility Analysis for HighFlexibility Analysis for HighTemperature Piping System -Temperature Piping System -
Case Study for Combined CycleCase Study for Combined CyclePower Plant.Power Plant.
What is Pipe ?What is Pipe ? It is a Tubular item made of metal, plastic, glass etc. meant for conveying Liquid,
Gas or any thing that flows. It is a very important component for any industrial plant. And it’s engineering plays
a major part in overall engineering of a Plant
High Temperature PipingHigh Temperature Piping In Power plant there are some piping which carries steam at high pressure and
temperature.. These pipes carries the main cycle steam and water of the steam power plant.
Pipe material selection - to withstand the high pressure and high temperature.
Steam pipes run at very high temperature and the hot pipes expand.There should be enough flexibility in these pipes so that pipe can itself withstand this thermal loading and high loads should not transferred to the nozzles of Turbine or Pumps.
Pipe Stress AnalysisPipe Stress Analysis The process of checking the stress developed in the piping due to various loading is called Pipe Stress Analysis/Flexibility analysis.
It is a discipline highly interrelated with piping layout and pipe support design and normally associated with analysis of stresses in a piping system, primarily due to thermal expansion or contraction.
The objective of the Pipe flexibility analysis is to ensure safety against failure of the piping material or anchor points from overstress.
Check pipe stresses with governing codes (as Design Base Document) .
Support load & movement for various loading conditions.
Check the terminal point loading (Forces & Moments) generated from pipe to the connected equipment.
Types of LoadsTypes of Loads
Sustained Loads– Dead Weight (Weight Of
Pipe, Fittings, Fluid in Pipe, Piping Components valves, valve Operators, flanges so on.)
Thermal Expansion Loads– Due to the Temperature
Occasional Loads– Seismic– Wind– Snow and etc.,
Also loads on piping can be classified as
Static Loads– Dead Weight– Thermal Expansion and
contraction effect– Effects of Support, anchor and
thermal movements– Internal and external loadings
Dynamic Loads– Impact forces– Wind Load– Seismic Load– Steam & Water Hammer effects– Discharge Loads
Stresses in PipingStresses in Piping
Hoop’s Stress Longitudinal Stress Axial Stress Radial Stress Bending Stress Torsion The failure of structural part occurs when a certain function of the
stress or strain components reaches a critical value. The peculiarity of the piping system is such that, there are possibilities of every possible stresses being generated in it
Stresses in Piping…..Contd.Stresses in Piping…..Contd. Circumferential stresses - Due to internal pressure Bending and torsional stresses - Due to dead load, snow and
ice, wind or earthquake. Primary stresses - Due to external effects are the direct
longitudinal Due to pressure inside the pipe - Three-dimensional stresses in
longitudinal, circumferential and radial direction are generated. Bending and torsional stress - Due to thermal expansion or
contraction because of temperature variations, bending and torsional stress are generated.
There are the direct, bending and torsional stresses - Due to the restrained thermal loadings (the restrained thermal analysis, the external forces being supplied in this case by the line of anchors and other restraints.)
Methods of Flexibility AnalysisMethods of Flexibility Analysis
Code Method Approximate Methods
– Guided Cantilever Method– Chart Solutions– Mitchell Bridge Method
Exact Analytical Methods– Simplified Kellogg's Method– General Kellogg's Method– Using Finite Element Technique
Model Tests
Finite Element MethodFinite Element Method
It is a numerical method of solution of complex problems, which is based on the general principle of "going from part to whole". Finite element method converts a continuous system into a discrete system. (Linear, three dimensional finite analysis program)
Derivation of finite element equations [K] * {u} = {F}
where,
[K] = global stiffness matrix,
{U} = global displacement vector,
{F} = global load vector
Pipe Flexibility AnalysisPipe Flexibility Analysis
Inputs and Various Steps in Flexibility Analysis– Geometric layout of Pipe– Pipe supporting configuration– Pipe Diameter and Thickness– Pressure inside Pipe– Cold and Hot temperatures of
Pipe– Weight of Pipe and insulation– Weight of carrying Fluid– Pipe material Property (Young’s
Modulus, Thermal Expansion Coefficient)
– Thrust on pipe due to blowing wind.
– Thrust on pipe due to earthquake
– Load of Snow on pipe
– Any transient loading like Steam Hammer load
– Any other load on the piping
Pipe Flexibility Analysis…Contd.Pipe Flexibility Analysis…Contd.
Piping Analysis Software
– PIPSYS is a PC-based computer program. This software package is an engineering tool used in the mechanical design and analysis of piping systems.
– There are many other commercial software available are SAP-IV, COSMOS/M, NISA, CAESAR-II & CAE PIPE.
Outputs
– Stress of the pipe at various loading conditions
– Load at various supports and restrains.
– Movement of pipe at support locations
– Pipe terminal point (anchor, equipment ) loading.
Piping FlexibilityPiping Flexibility
The major requirements in high temperature piping design is to provide adequate flexibility for in the piping system to allow the thermal expansion of the pipe without causing excessive stresses and without exceeding the terminal equipment allowable loadings.
Flexibility can be provided using Expansion loops, offsets, bends, etc., In piping designing, elbows, Bends, and Pipe Expansion Loops normally provide adequate flexibility for thermal expansion.– The stress can be reduced by introducing an expansion loop.– Expansion loops provided in the pipe length perpendicular to
the direction of straight pipe.
– The expansion of straight pipe will be accommodated between the anchors by flexing the loop legs, thus reducing the stress in
the pipe and loading on anchor.
Expansion LoopsExpansion Loops
Consideration for Piping FlexibilityConsideration for Piping Flexibility
Avoid the use of a straight pipe run of pipe between two-equipment connection or between two anchor points.
A piping system between two anchor points in a single plane shall have as a minimum configuration L-Shaped consisting of two runs of pipe and a single elbow.
A piping system between two anchor points with the piping in two planes may consist of Two L-Shaped runs of pipe. For e.g. One L-shaped run in the horizontal plane and another in vertical plane.
A three-plane configuration may consist of a series of L-shaped runs or U-shaped expansion loops designed into the normal routing of the system.
For high temperature piping following minimum consideration are required to ensure adequate flexibility :
– Adequate developed length of piping system between anchors/ equipment connection with in the physical design constraints as functional design requirements.
Consideration for Piping Consideration for Piping Flexibility….Contd..Flexibility….Contd..
– Provision of flexible supports, when up or down movement of pipe at support location will be made possible
– Provide single or multi direction restrain at strategic location to guide the pipe thermal expansion in a predictable manner and also to constraint where necessary.
– Further guides and restrain help to the control the excessive pipe rotation and resulting the stress in the pipe on moments on the equipment nozzle.
– Provide flexible supports in vertical raiser.
For systems consisting of large diameter main and numerous smaller branch lines, the designer must ascertain that the branches are flexible enough to with stand the expansion in the main header.
Systems that are purged by steam or hot gas must be reviewed to assure that they will be flexible during the purging operation.
Closed relief valve and hot blow down systems should be given special attentions.
Flexibility of Piping - ExampleFlexibility of Piping - Example
Flexibility of Piping - ExampleFlexibility of Piping - Example
Expansion Loop
Constant Load Spring
Variable Spring
Rig
id H
an
ger
Rig
id S
up
po
rt
Dynamic Support, Snubber
Rigid Support
Types of Pipe SupportsTypes of Pipe Supports
There are three general types
Rigid type (no flexibility in the direction of restrain)
Spring type (Allows pipe movement in direction of loading)
Dynamic Support (Degree of restrain depends on acceleration of load)
There are two types of spring support
Variable load type, here support load changes as the pipe moves.
Constant load support, the load remains constant within some range of movement.
Case Study for Combined Cycle for Combined Cycle Power PlantPower Plant
Main Steam Piping System The High Pressure (HP) steam system is designed per
ASME-B31.1(Power Piping Code) to convey HP superheated steam, from the HP superheater outlet to the high pressure section of the steam turbine. HP steam line is provided with a bypass line, with a combined pressure reducing and steam desuperheating valve and is connected to the Condenser.
Normal Operation Start-Up/Shutdown Operation
Piping Material SelectionPiping Material Selection
Piping material selection is based on established industry practices for the temperature, pressures, services and fluid type
General water and steam services less than 750 F ASTM A 106 Grade B or A53 Gr. B Steam Piping above 750 F less than 955 F ASTM A 335 Grade P11 Steam piping above 955 F to 1050 F ASTM A 335 Grade P 22 Steam piping above 1051 F to 1200 F ASTM A 335 Grade P 91 Flashing heater drain service ASTM A 335 Grade P5 Mild corrosive service ASTM A 312 or A 367, Grade TP304 Severe corrosive service ASTM A 312 or A 367, Grade TP316 Low pressure and temperature ASTM A-53 Grade B Concentrated acid handling systems Alloy 20 or HDPE / PVC / Rubber
lined Fire protection Carbon steel
Design dataDesign data Pipe Size = 8 inches for Main Steam Pipe Pipe Thickness = 160 Sch Insulation Thickness = 7.5 inches Pipe size = 24 inches for Bypass connection Pipe Thickness = STD Insulation Thickness = 2.5 inches Design Temperature = 955.4 ° F Design Pressure = 1450 psi Pipe Material = ASTM A335 P22 Insulation Material = Calcium silicate per ASTM C533 for heat retention Pipe Construction = Seamless Flange type = Not Allowed
Fittings Greater than 2 inch ASTM Spec. = A234 WP22 ASME STD. Type = B16.9, B16.28 Type = Butt Weld
Fittings Less than 2 inch ASTM Spec. = A182 F22 ASME STD. Type = B16.11 Rating = 9000 Class Type = Socket Weld Attemperator weight = 1322.5 lbs per 7.87ft
Stress/Node IsometricStress/Node Isometric
Analysis MethodologyAnalysis Methodology The Piping System is considered as an assembly of many pipe segments connected by analytical node
points.
The stress is computed based on internal forces and moments in each segment at all node points.
The reactions at each pipe support location are calculated; force equilibrium check is made at all node on support points.
The stress value as calculated in the analysis for sustained load and thermal expansion load at each node will be verified as per ASME B31.1 code equations for code compliance.
Dead weight AnalysisDead weight Analysis The PIPSYS checks the node formation and end connection of fittings, if it is properly sequenced it will
further proceed by forming a matrix for further analysis else error will be indicated for the specified Node and the same should be corrected.
it is checking the dead weight supporting is within the permissible limit. If the pipe is not properly supported in dead weight the support location should be changed to minimize the sag.
NODE TYPE FACTOR STRESS IN PSI DISPLACEMENTS IN INCHES (GLOBAL COORDINATE)
I (I*M)/Z X Y Z
--------------------------------------------------------------------
5 7 1.46 1389. 0.000 0.000 0.000
10 1 1.00 373. 0.000 -0.010 -0.001
Pipe Behaviour In Thermal Condition - Iteration -IPipe Behaviour In Thermal Condition - Iteration -I
Nodes Failing
Nodes Failing
Maximum stressed Node - Iteration IMaximum stressed Node - Iteration I
NODE NODE STRESS ALLOWABLE RATIO
TYPE (PSI) STRESS(PSI)
95 8 144000. 29180. 4.935
320 1 60800. 29028. 2.095
50 1 42200. 28083. 1.503
5 7 33000. 28619. 1.153
55 8 31400. 28639. 1.096 Ratio are more than 1, means that the stresses are exceeding the allowable stress limits and thus the nodes get
fails.
Equipment Nozzle reactionEquipment Nozzle reactionHrsgHrsg LOAD CASE FORCES (LBS) MOMENTS (FT-LBS)
HOT & WEIGHT FR = 4082. MR = 60244.
COLD & WEIGHT FR = 3516. MR = 72069
Turbine.Turbine. HOT & WEIGHT FR = 6068. MR = 36673.
COLD & WEIGHT FR = 6679. MR = 44044.
CondenserCondenser HOT & WEIGHT FR = 1102. MR = 6646.
COLD & WEIGHT FR = 1734. MR = 9026.
Pipe Behaviour In Thermal Condition - Iteration -IIPipe Behaviour In Thermal Condition - Iteration -II
Expansion Loops
Guide Support
Spring Hanger
Maximum stressed Node - Iteration IIMaximum stressed Node - Iteration II
NODE NODE STRESS ALLOWABLE RATIO
TYPE (PSI) STRESS(PSI)
325 11 24500. 29443. 0.832
305 8 21700. 29332. 0.740
5 7 19800. 28606. 0.692
330 7 18600. 29494. 0.631
55 8 16000. 28651. 0.558
95 8 14400. 29015. 0.496
Equipment Nozzle reactionEquipment Nozzle reactionHrsgHrsg LOAD CASE FORCES (LBS) MOMENTS (FT-LBS)
HOT & WEIGHT FR = 3924. MR = 56488.
COLD & WEIGHT FR = 3260. MR = 67373
Turbine.
HOT & WEIGHT FR = 5983. MR = 33526.
COLD & WEIGHT FR = 6503. MR = 40128
Condenser
HOT & WEIGHT FR = 1109. MR = 9508.
COLD & WEIGHT FR = 1674. MR = 12032.
Final IterationFinal Iteration
As the same Lot of trail and error iteration has been done to keep the pipe within permissible limit in dead weight, minimum stresses at all nodes and all the three equipment nozzles within the allowable limits as specified by the manufacturer of the same.
Finally by doing lot of iteration the best solution has arrived which gives
Minimum stresses in Piping Meets the code limits and Meets the Equipment forces and moments.
ConclusionConclusion
As seen in the case study in detail, the piping stress analysis checks with
The Acceptance of piping system per applicable design code, Requirement related to equipment limitation and
which ensures
The Safety of piping and piping components against failure Maintain system operability to comply with legislation / Indian boiler regulation the piping is well supported and does not sag or deflect in an unsightly way under its
own weight the deflections are well controlled when thermal and other loads are applied the loads and moments imposed on machinery and vessels by the thermal growth of
the attached piping are not excessive
Gives the input for
Input to civil for Structure design And loads and displacement for support design and for hanger design.
Thank YouThank You