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The Steam Trap Design Group

Date: Dec. 19, 2008 Faculty: Dr. Sadegh ME473 Students:

Ivan Pinzon David Rodriguez

Syed Hasan Luis Molina

Massamaghan Kone

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The Steam Trap Design Group Table Contents

NOMENCLATURE ........................................................................................................................................... 3

EXECUTIVE SUMMARY .................................................................................................................................. 5

INTRODUCTION ............................................................................................................................................. 7

PROBLEM STATEMENT .................................................................................................................................. 9

Gantt Chart ................................................................................................................................................. 16

Design Concept ........................................................................................................................................... 17

ANALYSIS ..................................................................................................................................................... 30

Heat transfer ............................................................................................................................................... 43

Energy Balance method for modeling the upward movement of a thermodynamic steam trap disc. ...... 45

NEW TECHNOLOGIES .................................................................................................................................. 48

CONCLUSION ............................................................................................................................................... 54

REFERENCES ................................................................................................................................................ 55

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NOMENCLATURE Name Abbreviation Units

Sustained Stress Expansion Stress Allowable stress

Internal Design Pressure Outer Pipe Diameter

Inner Pipe Diameter Thickness

Stress Intensification

Resultant Moment Stress Reduction Factor

Section Modulus Volumetric Flow Rate

Velocity Area with respect to outer and

inner diameter

Mass Flow Rate Hydraulic Diameter Reynolds Number

Kinematics Viscosity Friction Factor

Saturated Fluid Density Length of Pipe

Pressure Drop Head Loss due to fittings, valve

and other components

Head Loss due to friction Total Head Loss

Resistance Coefficient

Gravitational Acceleration Pressure Wave Velocity

Bulk Modulus Young’s Modulus Pressure due to water hammer

Maximum Pressure due to water hammer

Pressure increase due to valve closing

Maximum pressure increase to valve closing

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Time requires valve to close

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EXECUTIVE SUMMARY

On July 18, 2007, at the intersection of 41st and Lexington in Manhattan, New York, a

geyser of hot steam erupted for over 2 hours. The force from the steam shook the ground and

spewed mud and debris, thus creating a steam cloud over 1000 feet high. The blast made a

crater over 35 ft wide and 15 ft deep through the middle of the street. At first people did not

know what was the cause of the explosion but after careful examination it was determined to

be due to the water hammer effect. Excess condensate is routinely removed in stations called

steam trap assemblies. It was discovered that the devices that removed the condensate,

referred to as steam traps were severely clogged with debris and were not functioning

properly. As a result, the steam main at that intersection filled up with condensate, due to a

routine pressure change, a large steam bubble entered the region, and then imploded. The

surrounding condensate fills in the void faster than the speed of sound. The force generated

was greater than the pipe can withstand, thus allowing the steam to burst into the streets.

Our objective as mechanical engineering students at the City College of New York in

conjunction with Con Edison is to design a steam trap assembly. The three main objectives are:

to increase steam trap capacity, to prevent the steam trap from clogging, to apply a device that

remotely monitors the steam trap’s performance and that would alert Con Edison when the

traps are failing. During our design process, safety is our main concern given the circumstances.

Pressure and temperature analysis was the main concern when dealing with high pressure

water main systems. Factors such as stress analysis due to sustained and expansion loadings

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and heat transfer through the pipes were all incorporated into the selection process. The

materials, sizing and flow rate capacity for the steam trap assembly are dependent on the

results of the analysis. Solid modeling software such as Solidworks and Cosmosworks were

utilized in simulation and comparison of analysis.

The last aspect of the project was to implement a device that would remotely monitor

the steam trap. Several new technologies were considered such as: acoustic sensors and

ultrasonic flowmeters. Due to the expensive costs of these devices, further analysis will be

need in order to incorporate them into the next phase of the project. For the following

semester, an actual model will be assembled and we will attempt to simulate the conditions of

the steam trap assembly during normal operations. Our goal is to test the device that we

eventually select to detect when the trap is not working properly or if it’s completely clogged in

order to provide a means of remote monitoring. Hopefully our research will be a useful tool

that can be applied to future additions to steam trap monitoring systems.

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INTRODUCTION

Con Edison provides steam as a carrier of energy through 105 miles of piping systems in

New York, providing heat and energy clean and efficiently. Steam is known for its efficient

means of transferring heat. Steam is non-flammable and non-toxic thus making it safer when

compared to fuel oils. Con Edison has 3 plants that produce 50% of its steam through a process

called co-generation. During this process the steam leaves the boiler and then goes through

pipes into a turbine generator. The resulting spinning of the turbine blades produces electricity.

The remaining steam then goes into the steam system. This results in the elimination of 1.6

million tons of CO2 annually.

There are a number of factors that come into play in order to create conditions for an

explosion. The infrastructure under the streets is overcrowded, and the steam mains are

subject to water infiltration, if systems such water pipe or sewer leaks. The main consensus as

the cause of the explosion is a phenomena called water hammer effect. According to the ABS

report, “It is a phenomenon that can occur when cold water comes in contact with a hot steam

pipe, causing the steam inside to condense into liquid water, locally increasing the pressure,

causing the pipe to burst.” Other factors were also considered that contributed to this localized

pressure increase. Con Edison has designated areas along its main steam line that drain excess

condensate (water in liquid form) into stations called steam trap assemblies. The main

component that converts excess steam into condensate is called the steam trap. Steam traps

are automatic valves that selectively allows condensate to pass and traps steam and creates

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conditions that converts it back into its liquid form. In the Con Edison steam piping steam the

condensate is drained into the sewer system and therefore having unnecessary steam in the

sewer system is unfavorable.

Upon investigation, the steam traps failed to remove the condensate on that day for

two reasons. First there was heavy runoff from 1.59 inches of rainfall in a 5 hour period. Cold

water on the surface cooling the steam in contact with the pipe created a significant amount of

condensate. The condensate fills the pipe at the lowest point, the steam bubble forms and the

rupture occurred in a rising pipe bend section. The steam trap assembly was unable to remove

the condensate due to lack of flow. It was discovered that the traps that were used on 41st and

Lexington were almost completely clogged. Upon removal it was discovered that the

substances in the clog were metallic substances that have collected over the years which have

reduced the flow of condensate unnoticeably and compromised the ability of the steam traps

to remove condensate. It was discovered that the manholes that morning were releasing

steam, which was a clue to what was happening. However there is no automatic system in

place to notify Con Edison when there is too much condensate in the steam mains. It is

important to keep safety first in investing in steam operations in order to avoid accidents such

as the one in midtown in 2007.

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PROBLEM STATEMENT

Objectives

The main objective of this project is to re-engineer the steam trap system so that all the

causes of the explosion can be diminished or avoided entirely. The primary cause of the

explosion was clogging of the steam trap due to debris and sealant. The debris came from a

source of erosion of the pipes interior wall. The sealant was present because it leaked in after

previous maintenance work done on leaky pipes throughout the system. The combination of

the debris and sealant lead to the grave explosion, which occurred on July 18, 2007 at East 41st

Street and Lexington Avenue. The explosion happened because the traps were clogged, steam

and condensate began to build up, the steam bubble formed and burst, causing intense

shockwaves due to the water hammer effect.

The type of water hammer that occurred in the system was a condensation-induced

water hammer effect. This kind of water hammer occurs when steam collapses into condensate

creating a void thus causing the condensate to rush in to fill the void and smash into itself. This

then creates a pressure pulse that can reach magnitudes of 1,000 to 2,000 psig. This pulse then

traveled through the condensate at the speed of sound in a fluid, 4,000 ft/s, combined with the

internal loadings and stresses of the pipes it exceeded the material strength of the pipes and

the pipe ruptured. The objective here would be to find a way of preventing the steam traps

from getting clogged.

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After determining a way of preventing the steam traps from getting clogged the next

objective would be to increase the capacity of the steam trap system. Now this is an open-

ended problem because there is more than one way of increasing the capacity of the steam

trap system. The trap itself can be re-designed to increase capacity or the system can be re-

designed so as to include more traps, thus increasing the capacity of the system. Our challenge

here is determining which method of increasing the capacity of the system is the most efficient,

cost-effective, and works best with our constraints.

The next objective of the project was to develop a remote monitoring system. Con

Edison wants to develop a system that will allow them to monitor the steam trap system from

their plant. The problem here is the extreme conditions within the manhole chamber in which

the steam trap system is located are not ideal for sensors. The temperature in the chamber is

212°F and there is a high oxidation rate, there are very limited sensors that would survive in

that kind of environment. Placing sensors within the piping system itself is a problem as well

because of pipe erosion, high temperature, and once again oxidation. The challenge here is to

try and find a technology that can determine whether or not the steam traps are working

properly as well as withstand the extreme conditions of the steam trap chamber.

Another objective of the project is to calculate internal pressures and stresses at key

points in the steam trap system. For this a thorough understanding of fluid dynamics, stress,

and heat transfer analysis in pipes is needed. The formulas needed to carry out these

calculations were obtained from a number of mechanical engineering handbooks. The results of

this objective will be compared with the results of FEM analysis that will be done using

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SolidWorks, CosmosWorks, FlowWorks, and ANSYS. This objective will be the most time

consuming due to errors in calculations, and determining how to setup the correct boundary

conditions for the analysis.

The next objective would be material selection. This is a very important aspect of the

project because of the environment of the steam trap chamber. Not all materials would be able

to survive under those extreme conditions. In addition to the life span of materials we would

need to select materials that would be able to sustain the pressures and stresses obtained from

the calculations of stresses and pressures. Steel and Iron pipes are not a good fit because of

oxidation; these systems are intended to last many years and using pipes made from these

materials would require frequent maintenance of the system. The challenge here is to be able

to determine which materials will be able to sustain the loads, pressures, and stresses as well as

resist erosion and oxidation.

Specifications

There were certain specifications and constraints given for this project. One was size

constraint. The chamber of the manhole has a measurement of 4 ft tall by 3 ft wide by 2 ft

deep. This constraint was essential in our designs because it restricted the variation of the

assembly of the system. Another constraint that applied to the manhole chamber is that all the

valves must be installed with the knobs facing upward at a 45° angle. This allows for Con Edison

maintenance workers to easily access the valves from the street using a special apparatus.

Specifications of the inlet parameters were given to us as well. The inlet pressure of the

system is 180 psig. The inlet temperature is 381° F and the mass flow rate at the inlet header is

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2300 lbm/hr. The ambient temperature of the chamber is in the range of 212-250° F. These

specifications were important in our hand calculations for fluid dynamics, stress analysis, and

heat transfer analysis. The calculations and specifications were instrumental in the selection of

material.

Steps Taken

The proposition of strainers was the solution to trap clogging. Strainers come in all

shape and sizes. A strainers job is to act as a filter in a pipeline; it contains a cylindrical screen

that traps foreign particles in the fluid. The size of the holes in the screen determines the size of

the particles that are allowed through. Some steam traps come with a strainer already

implemented in it, it is something that we are considering.

In order to increase the capacity of the steam trap system from 4600 lbm/hr to 8000

lbm/hr there were two methods that can be employed. The first method would be to increase

the capacity of each steam trap itself. This is the more difficult and time consuming (in terms of

design) of the two methods. Increasing the capacity of the trap would allow a greater flow rate

through it but many aspects must be taken into account when doing this. The most important

aspect is the backpressure of the system. If not designed correctly the trap may be caused to

fail and depending on the backpressure it could fail open, which would be good in terms of

safety, or it could fail closed, which would lead to the same outcome as if the trap were

clogged. The second method would be to increase the number of lines with steam traps. This

would allow us to use a larger quantity of the same steam traps that are already in use in the

system. The flow rate that goes through the system can be increased by the capacity of each

trap. This method is more feasible and can be implemented into designs with more ease.

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The solution to remote monitoring of the system has not yet been determined. We have

looked into a number of sensors and technologies trying to determine which would be best

suited for our system. Once again the problem here are the extreme conditions of the chamber

of the manhole as well as inside the pipes, not many sensors would survive very long under

these conditions. We have found some technologies that offer potential but most would be too

expensive to purchase for this purpose. We intend to continue to look at the technologies with

potential as well as try and find some others. The solution that Con Edison suggested was the

use of two thermal couples per steam trap. This would allow them to monitor the temperature

of the pipe as the fluid comes out of the trap, if the temperature is fluctuating between

ambient temperature and the temperature of the fluid then the trap is working, if the

temperature stays constant (such as reading the ambient temperature) that means the trap is

not working. This solution works but it also adds length to the assembly, which is not good in

regards to our space constraint.

The calculation of stresses inside the pipes took some time in terms of investigating the

correct formulas to use as well as getting reasonable numbers from our calculations. The

calculations included two-phase fluid dynamics in a pipe; stress analysis due to static loading,

internal pressures, and thermal expansion; and heat transfer analysis on the system

(Conduction through pipes and Convection with Ambient Air). The material for the system was

given to us by Con Edison to be red brass for the pipes, bronze for the valves, and steel for the

strainers and steam traps. The solid modeling for the project was done using SolidWorks, while

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the analysis was tried in ANSYS but to no luck. None of the group members were able to master

the program in time to get the results, so FlowWorks and CosmosWorks were used instead.

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Gantt Chart

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Design Concept

In order to begin the design a starting point was need so to start a simple question was

to be answered: what are some of the important factors that are desired for the design? Having

a starting point can allow for the expansion and implementation of ideas that were gathered

through brainstorming. A simple flowchart was constructed in order to assist the design process

(shown below). One of the important design selections was selecting a steam trap that would

sustain the condition of the manhole it will be in. Since there are different types of steam traps

they will be discussed in detail including why some were not suitable.

Many of the steam traps used to remove condensate fall into three different categories:

Mechanical, Thermostatic, and Thermodynamic. Mechanical traps utilize the difference in

densities of steam and condensate in order to detect any such presence of condensate.

Examples of the mechanical traps include the Inverted Bucket trap and the float thermostatic

trap (figure 1 and figure 2 respectively.)

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Figure 1- Inverted Bucket Trap.

Figure 2- Float and thermostatic trap.

For the inverted bucket, condensate flows around the bucket discharging

through the open valve. Steam the collects in the top of the bucket, due to the buoyancy of the

steam the bucket raises closing the valve. Float and thermostatic traps follow the condensate

level in its chamber in order to open the discharge valve. Due to this reason there is a constant

water level within the trap resulting in a continuous discharge. The thermostatic element within

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the trap purges air and other gases at temperatures lower than saturation temperature of the

steam.

The next category of traps is the thermostatic trap or temperature controlled traps.

They function by using an alcohol mixture; the temperature difference of the mixture’s boiling

point and the surrounding condensate is exploited through this method. It is important to note

that there two types of thermostatic traps one being the bellows trap and the other the liquid

capsule trap. Both traps function similarly where as the condensate reaches steam temperature

the alcohol mixture reaches its boiling point causing this mixture to evaporate.

So as the mixture is evaporating it begins to expand with the capsule causing the

internal pressure of the capsule or the bellows to increase. This force is greater that within the

trap thereby causing the valve to close, preventing steam from blowing out of the trap. So as

the steam turns into condensate, the temperature inside the trap drops causing the alcohol

mixture to recondense lifting the valve off its seat.

(a) (b)

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FIG 3- Liquid Capsule Trap filled with isopropanol mixture. In (a) valve is opened, in (b) the capsule has expanded causing valve to close.

A very important aspect of the thermostatic trap is the mixture of distilled water and

alcohol inside the bellows or capsule for determining operating temperature. But most

importantly it must be noted that thermostatic traps will cause condensate to backup in the

system. The amount of condensate that is backed up is dependent upon the temperature the

trap was designed for. Thermostatic traps can work up to 250 psig and will provide consistent

periods of subcooling condensate with respect to the steam.

FIG. 4- Bellows Type Steam Trap.

Other types of thermostatic traps include bimetallic traps; these traps uses a bimetal

stack made from two different metals. These two metals are 304 and 316 stainless steel where

one expands more than the other at a given temperature due to different coefficient of

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expansions. As the stack expands it tends to bend or arch causing the valve to close or open in

an accordingly manner.

FIG 5- Bimetallic Steam Trap with a close up of bimetallic stack.

Bimetallic traps have extensive subcooling ranges which can reach to almost 100oF

below saturation temperatures. As a result of this large amounts of condensate are backed

within the system similar to the other thermostatic trap. Bimetallic traps are able to withstand

waterhammer but are also more susceptible to it due to large amounts of backed up

condensate. Though bimetallic traps suffer from lag time in responding to large loads of

steam/condensate they are able to withstand a lot lower temperatures than most other steam

traps. Those traps that do not have low temperature limits are inhibited by subcooling

temperatures and are not suited for those types of environments.

One last type of thermostatic trap to mention is the liquid expansion trap. These types

of traps function similarly to the bellows type except that instead of alcohol mixture a mineral

oil is used. As condensate begins to enter the trap the temperature of the oil begins to rise

causing to expand within its capsule. Due to the expansion the oil exerts a force on the end of

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the bellow causing the plunger valve to close. One other characteristic that is different in the

liquid expansion trap is the presence of an adjustable nut. This nut is then adjusted for the

desired temperature range under which condensate is discharged.

FIG. 6- Liquid Expansion Trap.

For this reason liquid expansion trap can be utilized as an inexpensive temperature

regulator on an as needed basis. Liquid expansion traps primarily can be used for hot water that

must be kept below steam temperature. Though they have the ability to have adjustable

discharge temperatures, liquid expansion traps are prone to back up condensate as well. In

addition liquid expansion traps are unable to rapidly respond to a change in loads making them

more susceptible to waterhammer.

The last trap to be discussed is the Thermodynamic (disk) trap. These types of traps

discharge condensate at an intermittent rate by using a dynamic effect caused by flash steam

passing through it. The incoming pressure at start-up raises the disc allowing air and cool

condensate to be discharged immediately (Figure 7A). As condensate flows into the chamber its

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temperature reaches that of saturation temperature releasing flash steam that is moving at a

high velocity. The high velocity that it is created as a result of flash steam creates a low pressure

area below the disc pulling it towards the seat (Figure 7B).

FIG. 7A FIG. 7B

The buildup of pressure inside the chamber as a result of flash steam pushes against the

disk that the completely snaps the disk shut onto the seat (FIG. 8A). At the instant the disk is

shut the pressure above the disk is equal to the pressure upstream (FIG. 8B). Now the reason

the disk is maintained closed is due to the fact that the pressurized area above the disc is larger

than the area of the inlet.

The flash steam trapped in the upper chamber begins to lose pressure as it begins to

become condensate or many cases air is leaked through a micro-bleed. So as soon as the

pressure is low enough condensate is discharged, the disk is lifted up off its seat as the cycle

repeats. A lot of thermodynamic traps have a built in strainer thereby reducing the amount

space used in the steam trap station.

Disk

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FIG. 8A FIG. 8B

There are different kinds of traps for different applications, so it is important to select

the correct trap for it to be effective in the steam system. The selection depends on different

parameters such as the pressure the system is at, temperature and the amount of load it can

handle (Table 1).

Criteria Inverted Bucket

Thermodynamic Thermostatic F&T

Air Venting Low Low High Medium/High

Application Drip Legs, Process Equip.

Drip Legs, Tracing Drip Legs, Process Equip.,

Tracing

Drip Legs, Process Equip.

Resistant to Water Hammer

Yes Yes No No

Relative Cost Medium/Low Low Low Medium/High

Ease of Maintenance

Moderate Very Easy Very Easy Moderate

Capacity High Low Medium High

Pressure Range Up to 250 psig

Up to 600 psig Up to 125 psig Up to 250 psig

Figure Criteria for Steam Trap Selection

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Next to be discussed is another component of a steam trap assembly and it is valves.

The purpose of valves is so that there is proper control and regulation with respect to steam

pressure. For this design one of the valves used was the gate valve which is also known as the

sluice valve. A distinctive feature of the gate valve (FIG. 9) is the planar surface between the

gate and seat which serves as the sealing surface. This valve is opened by lifting a round or

rectangular gate out from the incoming fluid. Because the gate valve retracts fully when opened

there is a minimal pressure loss in the fluid as it passes through the pipe.

FIG. 9- Solid model of gate valve from steam trap assembly cad model.

The most important thing to consider in the design of a new steam trap assembly is keeping

from clogging. The fact that the trap was clogged was one of the factors that lead to the

incident on Lexington Avenue and 41st. The figures below are comparisons of the old and

current steam trap assembly.

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FIG. 10- Old steam trap assembly design that failed as a result of clogged steam traps.

FIG. 11- Current steam trap assembly design.

The problem with the old design (FIG. 10) is that there was no implementation in

keeping the assembly free of any debris. So as a result what ever debris that was in the pipe line

made its way through to the steam trap assembly. After a certain amount of time the steam

traps just got clogged and no condensate was being discharged as rapidly as it should.

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Therefore in order to remedy the clogging problem Con Ed added Y-strainers into the steam

trap assembly. These strainers have a mesh within its cavity with holes for fluid to pass through.

The smallest particle size would determine the mesh size, for different mesh sizes there is a

maximum particle size it can filter (table 2).

Relationship of Mesh Size and Particle diameter Mesh size Particle Diameter (μm)

4 5,205 8 2,487

10 1,923 14 1,3007 18 1,000 20 840 25 710 30 590 35 500

Table 2- Relationship of mesh size with respect to particle diameter (μm).

In addition the sizes of the inlet and outlet headers were increased from one inch to two

inch in the current design. The reason for this was to allow particle settling and reduce some

backpressure before condensate went into steam trap lines. One of the Steam Trap Designers

own concept is shown below.

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FIG. 12- Design Concept One

In this concept the inlet header would have a nominal pipe size of three inches; in

addition there would be strainers in the lines to prevent clogging. The design concept would

also have temperature sensors in order to monitor the temperature of condensate, if the

condensate would reach the high limit on the set parameter it would be know whether or not

the trap had failed/clogged. Although this design concept was very good there were a couple

problems with this design one being the amount of space it required. The amount of space

inside the manhole would not have sufficed for this concept; in addition the valves would not

be able to be adjusted from street level.

So for next concept, what was kept in mind was increasing the capacity of the steam

trap assembly while also keeping or reducing the amount of space needed (see figure below).

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FIG. 11- Design Concept Two

In this design concept the bypass line that exists in the current ConEd assembly has been eliminated.

Instead all three lines have thermodynamic traps with strainers and a bypass line is going out from the

first valve connecting to valve following the trap in each line. Components have been eliminated, weight

has been reduced, and capacity has been increased to a total of approximately 8000 lbs/hr. In addition

maintenance of the assembly is very easy, without losing much capacity when working on one line, and

valves are easily accessible from street level by using a handle with claw end to turn them. For the

moment this is the design the group will go with; other technologies being considered will be discussed

later in this report. For all steam trap assemblies red brass pipe was used because it is more corrosion

resistant than stainless steel pipes when steam or condensate is the medium and is able to withstand

the harsh conditions of the manhole .

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ANALYSIS

The analysis of the following steam trap assembly has been divided into two parts for the Con-Edison purposed model and the design concept that we have purposed. First part contains the stress analysis and the second part is the analysis with respect fluids (saturated water at 200 Psig).

STRESS ANALYSIS

The power piping codes are included but are not limited to the steam, water, gas, oil and air services. In other industrial application these codes are applicable as well. Design requirements in this code includes for pipes, flanges, gaskets, valves, relief devices, fittings, and pressure-containing parts of the piping components. The loading requires for the following system are pressure, weight (live, dead and under test loads), impact (fluid hammer), wind, vibration and earthquakes (if applicable). Therefore once any piping system has been designed it requires passing the stresses or any failure due to loadings. Hence for the system we are analyzing two stresses are very important and those are as follows:

1. Stresses due to sustained loadings 2. Stresses due to expansion loadings

STRESSES DUE TO SUSTAINED LOADINGS

Stress of a type has been already formulated and given in most of the handbooks thus it can be determined as,

STRESSES DUE TO EXPANSION LOADINGS

Similarly stress due to expansion loadings also have been formulated and given in many of the piping handbooks thus it can also be determined as,

Loading Types Con-Edison Assembly Conceptual Design Assembly

Allowable Stresses

Sustained Loadings (ksi) 1.6387 1.4325 5.1150 Expansion Loadings (ksi) 1.5919 1.1768 8.3913

Stress due to loadings

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FLUID ANALYSIS

The fluid analysis for the particular type of structure or assembly is not easy and cannot be done in one shot. Thus it may required series of calculation and might require iterating the problems in determining the desire unknown values. With respect to the fluid flow in any piping system there are three important concepts always required to keep in mind. Those concepts are as follows:

1. PRESSURE DROP- The drop in pressure caused by viscous effects during the fluid flow through the pipes or ducts.

2. HEAD LOSS-A pressure loss of fluid in terms of fluid height either due to friction or change in velocity. The head loss can be major that will be due to the friction and minor due to the valve or any other fitting or components.

3. BACK PRESSURE-A pressure that is created by water hammer due to the sudden stoppage of flow when a valve or closing component (Thermodynamic steam traps) closes rapidly. Such type of a pressure also called HAMMER PRESSURE.

FROM POINT-1 TO POINT-2

Fluid flow from point-1 to point-2

VELOCITY DETERMINATION

Since the mass flow rate is known thus the entrance velocity in the header and the velocity at 1st horizontal pipe can be determined. Thus the velocities can be calculated as

The volumetric flow rate then can be determined as,

1

2

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Thus the velocity with respect to the point-2 can finally be determined and is given as,

PRESSURE DROP CALCULATION

In determining pressure drop it is important to know the type of the flow through the pipe, thus the Reynolds number are required to determine. Hence it can be calculated as

Once the Reynolds numbers are obtained as Laminar flow then using Darcy equation friction factor can be determined. But, on the other hand if the flow is turbulent then friction factor can be determined using Colebrook equation. Therefore considering a turbulent flow as the application indicates friction factor can be calculated either using Moody’s chart or the equation given below as

Where

The above A, B and C are the constant coefficients that are known as Serghide’s solution for the Colebrook equation that is often use in practice rather than Moody’s chart. It allows reducing the percent of error due to reading the graph.

Finally the pressure drop can be determined and is given as,

HEAD LOSS CALCULATION

Since the pipe are connected through a Tee-Socket therefore a minor head loss is expected during the calculations and can be determined as,

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Similarly major loss also will occur during the flow through the pipe and it also can be determined as,

Finally the total head loss can be determined and is given as,

Con-Edison Purposed Assembly Conceptual Design Assembly

0.0020514 0.0020514

0.004669 0.004669

0.010828 0.010828

0.015497 0.015497

FROM POINT-1 TO POINT-3

Fluid flow from point-1 to point-3

Similar analysis will be used to analyze the fluid flow from point of entrance of the fluid to the 2nd horizontal pipe which is considered to be the point-3 of the vertical inlet header. The major difference in

1

2

3

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the study will be pressure drop, minor head loss and major head loss due to the two Tee-Sockets and also length plays another important factor in pressure drop.

Con-Edison Purposed Assembly Conceptual Design Assembly

0.003608 0.003608

0.009338 0.009338

0.019041 0.019041

0.028380 0.028380

FROM POINT-1 TO POINT-4

Fluid flow from point-1 to point-4

Con-Edison Purposed Assembly Conceptual Design Assembly

0.001134 0.001134

0.002350 0.002350

0.005983 0.005983

0.008333 0.008333

1

2

3

4

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FROM POINT-1 TO POINT-4

Fluid flow through header

Con-Edison Purposed Assembly

0.001378

0.008460

0.007273

0.015733

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HORIZONTAL PIPE ANALYSIS

PIPE-1

Fluid flow in horizontal pipe-1

As far as the pressure drop and head losses concerned they can be obtained analytically same way as the inlet header has been solved.

BACK PRESSURE DETERMINATION

The fluid flow in a horizontal pipe is little complex not because of joining by valves and the other joining component. But, steam trap is the complex component that creates the problem. Thus in the following analysis there is a slight chance of less head loss due to other joining components beside the steam trap that may affect on the flow creating large head loss due to back pressure that is also called hammer pressure.

Since the pressure goes down when fluid reaches to the horizontal pipe, thus all the properties must be required to obtain at the following operating pressure. In this case of study the operating pressure has suggested to be at 180 Psig.

Since the fluid will be flowing within this part at the speed of sound that is equal to be 4720 ft/s therefore the velocity of the pressure wave can be determined. Hence it is calculated as,

The velocity has been previously determined at point-2 (See flow from point-1 to point-2), therefore it can simply be considered that velocity for the liquid will remains almost same. But, can be calculated as,

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The pressure within the pipe will increase due to the water hammer that can be determined and is given as,

The maximum pressure due to the water hammer can be obtained to see how much pressure the pipe can easily be hold due to the water hammer affect. Therefore it can be calculated as,

Finally, the pressure rise can be determined that is caused by the opening and closing of the steam trap. Thus it is given as,

Similarly, the maximum operating pressure due to the opening and closing the steam trap can also be determined and is given as,

It is very important in such type of calculation that the closing time of the closure valve is rapid such that the valve is completely closed before the negative pressure wave returns to the valve. In other words

the closure time must be less than , also very important is to carry out the right unit system.

Con-Edison Purposed Assembly Conceptual Design Assembly

0.029120 0.022120

0.070393 0.050393

0.153128 0.100128

0.223543 0.150521

264.39 264.39

453.39 453.39

264.39 264.39

453.39 453.39

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PIPE-2

Fluid flow in horizontal pipe-2

Con-Edison Purposed Assembly Conceptual Design Assembly

0.029166 0.023356

0.070575 0.069231

0.153566 0.112456

0.224163 0.181687

264.7 264.7

458.7 458.7

264.7 264.7

458.7 458.7

During the back pressure calculation it has been noticed that the pressure increased by water hammer and pressure increased by closing and opening of a steam trap for both the horizontal pipe has been noticed to be same. It is because the length of the pipe is relatively smaller and such type of pressure increases largely depend upon the length of the pipes.

SOLID MODELING OF TRAPS AND STRAINER

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Figure: Spirax TD-52 solid model

Figure: Strainer

FEA ON PIPING ASSEMBLY

40

Piping Assembly

41

Von Misses Stress Plot

Stress in Y-Direction

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Deformation Plot

For the FEA analysis the entire assembly was modeled as a part and the loads included the

weight of the pipe and the weights of the steam trap, valves, strainers, etc.

Maximum overall von mises 279 psi

Displacement Y direction 0.000357 inches

As it was expected there was no much deformation do to the loadings and also the comparison of Von

Misses stress to the stress in y-direction shows that the bending stresses are within the range. The

steam trap assembly is very stable for almost any kind of configuration, due to the light weight of the

parts, and the fact that it is not a moving part. Since we would be using standard pipes and not

manufacturing our own, we would use the loading constraints specified by the manufacturer. Instead

heat transfer would be more important to analyze along the pipe.

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Heat transfer

This report details the analysis and the result of the heat transfer analysis performed on the

steam trap. Heat losses due to friction and other factors such as convection and conduction through

valves, fittings and other piping elements are neglected here.

Before elaborating the formulas and the procedure used, we would like to specify the status of

our flow. Saturated Water, mainly condensate, flows through pipes until it reaches the steam trap

where most the steam is extracted from the mixture, condensed and drained along with the condensate

out to the pipe leading to the sewer.

To facilitate our analysis, we will assume the assembly to be simply made of pipes. Valves, traps

and other components are eliminated. Even though, heat is tremendously lost in the traps, we will

assume them inexistent to facilitate our analysis (See figure below).

Figure: Simplification of the Trap assembly for Heat Transfer Calculations

The following table details the inlet and outlet conditions. In addition, other factors such as ambient

temperature are added. Also, we assumed the flow to be purely condensate.

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Inlet Conditions Outlet conditions Pressure 180 Psi 14.7 psi or 29.82 Psi Temperature 373.1 F 212F or 250 F Mass flow rate 2300 lbm/hr 2300 lbm/hr

Additional information given about the pipes dimensions are also considered in the analysis. It’s clear that the equations describing the system are those of an internal flow. Since the fluid is considered saturated water mainly condensate, we have accumulated the necessary properties at the conditions specified above.

The following set of equations is used in the order presented.

After hand and Matlab computations, we found out that the flow is turbulent (Re>2300). Additionally, the heat transferred due to convection to the surrounding is approximate to be 5500 Btu/hr.

Still interested to the heat transferred, we have performed additional evaluations, notably using FloWorks, a computer software. We devise the assembly according to the data presented above and simulate the heat losses by analyzing the decrease of temperature as the fluid flows through the assembly. As such we have these visual graphics.

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Figure: Temperature Distribution for the Pipe Subjected To Heat Losses

As we expected, Heat is lost as it goes along the pipes, resulting to a cooler liquid when we reach the outlet. This is a more general analysis. With a trap, we expect more heat losses.

When it comes to our own design, we would like to emphasize that a heat transfer analysis is practically useless for both elements are simply the same. We have however diminished the amount of elements on the whole assembly.

Energy Balance method for modeling the upward movement of a thermodynamic steam trap disc. Assumptions: Closed system, mass constant above the disk.

Kinetic and potential energy changes are negligible. Friction between the disk and cylinder is negligible.

Analysis:

H2

H20- steam 180 Psi 373.1 ⁰F

Q H20 14.7 Psi 212 ⁰F

State 1 State 2

Wb

H1

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Where: u- internal energy m- mass per unit volume v- specific volume V- volume H- height D -diameter of disk T –temperature P –pressure Wb –boundary work Q -heat Ein-Eout=∆E Qout – Win= ∆U Qout =Win+ m (u1-u2) State 1: P1 =180 Psi v1= 0.0183 ft3/lbm T1= 373.1 ⁰F u1= 345.5766 Btu/lbm To obtain V1: D= 1.356 in Ac= 1.44 in2 H1=0.119 in V1= Ac*H1= 0.17136 in3 = 9.9167 e-5 ft3 m= V1/v1 = 9.9167 e-5 (ft3) / 0.0183 (ft3/lbm) = 5.415 e-3 (lbm) To obtain V2: D= 1.356 in Ac= 1.44 in2 H2=0.0108 in V2= Ac*H2= 0.015647 in3 = 9.055149 e-5 ft3 v2=V2/m= 9.055149 e-5 ft3 / 5.415 e-3 (lbm) v2=0.001671 ft3/lbm State 2: P2 =14.7 Psi T2= 211.95 ⁰F V2= 0.001671 ft3/lbm u2= 180.1199 Btu/lbm The boundary work during this process is the area under the process P-V curve.

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Assuming a linear change:

Wb= (P1+P2)/2 * (V2-V1) = (180 + 14.7 psi)/2 * (9.9167*e-5 -9.055149*e-5 ft3)* (1 Btu/5.40395 psia*ft3) = 0.04745 Btu The Heat Loss is: Qout =Win+ m (u1-u2) = 0.04745 Btu + 5.415 e-3 lbm *( 345.5766 -180.1199) Btu/lbm = 0.849205 BTU The heat is transferred out of the system and the boundary work is done to the steam and thereby temperature and pressure decrease in a linear fashion as the disk moves upward. The position of the disk can then be determined if you know the pressure of the steam at any given time.

1

2

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NEW TECHNOLOGIES

Ultrasonic Flowmeters

An ultrasonic flow meter measures the velocity of a liquid or gas through a pipe using ultrasonic

transducers. The results are slightly affected by temperature, density or viscosity of the flowing medium.

Ultrasonic flowmeters operate on this principle, using sound waves in the ultrasonic range (typically at a

frequency of 1 MHz). Ultrasonic (or acoustic) flowmeters operate by generating sound waves with a

transducer and measuring the propagation of those waves through a flowing fluid. There are two basic

kinds of ultrasonic flowmeters: transit time and Doppler-effect (or frequency shift) flowmeters. The

transit time flowmeter transmits sound waves in the upstream and downstream directions and

measures the difference in travel time. A typical transit time ultrasonic meter is shown schematically in

the figure below.

Figure: Transit Line equipped with Ultrasonic Flowmeter

It involves two transducers that alternately transmit and receive ultrasonic waves, one in the direction

of flow and the other in the opposite direction. The travel time for each direction can be measured

accurately, and the difference in the travel time can be calculated.

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Doppler-effect ultrasonic flowmeters measure the average flow velocity along the sonic path. This is

done by clamping a piezoelectric transducer on the outside surface of a pipe (or pressing the transducer

against the pipe for handheld units). The transducer transmits a sound wave at a fixed frequency

through the pipe wall and into the flowing liquid. The waves reflected by impurities, such as suspended

solid particles or entrained gas bubbles, are relayed to a receiving transducer. The change in the

frequency of the reflected waves is proportional to the flow velocity, and a microprocessor determines

the flow velocity by comparing the frequency shift between the transmitted and reflected signals. The

flow rate and the total amount of flow can also be determined using the measured velocity by properly

configuring the flowmeter for the given pipe and flow conditions. The operation of ultrasonic

flowmeters depends on the ultrasound waves being reflected off discontinuities in density.

Ultrasonic flowmeters have the following advantages:

• They are easy and quick to install by clamping them on the outside of pipes of 0.6 cm to over 3

m in diameter, and even on open channels.

• They are nonintrusive. Since the meters clamp on, there is no need to stop operation and drill

holes into piping, and no production downtime.

• There is no pressure drop since the meters do not interfere with the flow.

• Since there is no direct contact with the fluid, there is no danger of corrosion or clogging.

• They are suitable for a wide range of fluids from toxic chemicals to slurries to clean liquids, for

permanent or temporary flow measurement.

• There are no moving parts, and thus the meters provide reliable and maintenance-free

operation.

• They can also measure flow quantities in reverse flow.

• The quoted accuracies are 1 to 2 percent.

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Ultrasonic flowmeters are noninvasive devices, and the ultrasonic transducers can effectively transmit

signals through polyvinyl chloride (PVC), steel, iron, and brass walls. If added into our design, it will help

reduce the space used by the bushing adapter for the thermocouples. Plus, it will help prevent cloaking

and warn of air bubbles formations. Additional information as to pipe cloaking and sizes of debris

traveling in the flow can also be detected. This is can efficiently help prevent another explosion. Even

though being widespread on the market, we are still searching for a cheap ultrasonic flowmeters. They

tend to be very expenses.

A trap usually requires a valve (maybe two, one upstream and one downstream), a strainer or a filtering

system, a most importantly a by-pass system, in case of cloaking. These elements along with piping

connections in between following different arrangements produce a steam trap assembly. Our design

simply combines a steam trap with a strainer with by-pass system associated with each line, parallel to

the main-line.

While researching new and yet efficient technologies, we encountered different types of elements. One

that certainly caught our attention, for its simplicity, is the Velan Forged Piping King Automatic

Condensate Drain Units ®.The Piping King Package unit fitted with a bypass, enables the steam trap to

be isolated from the system allowing routine maintenance to be carried out.

The unit consists of a steam trap with integral strainer and check valve and of two high-quality forged

steel special stop check globe valves mounted on either side of the trap. The valves are connected by

the bypass pipe, enabling the steam trap to be isolated while the steam flow is maintained. The

manufacturers are proud to specify that it reduces spaces in assembly and easy to mount, as it is shown

in the figure below.

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Figure: Graphics Depicting the Utility and the Space-Saving of the Piping King Units

The working principal of the Piping King Units is simple. We will break it up in 4 steps:

1. AUTOMATIC STEAM TRAP OPERATION

Inlet valve and outlet valve both in top, closed position to provide double protection against leakage through the bypass.

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2. COMPLETE SHUTOFF - NO FLOW TRAP ISOLATED FOR SERVICE

Inlet valve in bottom position, outlet valve in top position. The trap is now sealed off by the inlet valve and the bypass is closed by the outlet valve. The valve is protected from back-pressure by the check valve portion of the outlet valve.

3. BYPASS OPEN - FULL FLOW TRAP ISOLATED FOR SERVICE PREFERRED SERVICE POSITION

Both inlet valve and outlet valves in bottom position to seal off the trap against flow and back-pressure. Trap is isolated and ready for service.

4. THROTTLED BY-PASSING - TRAP ISOLATED FOR SERVICE

Inlet valve in bottom position, outlet valve in intermediate position. The trap is sealed off by the inlet valve and flow through the bypass is restricted by the position of the outlet valve. The floating check valve of the outlet valve protects the trap from back pressure.

53

Velan Piping Kings can be installed in any position, and require only a minimal amount of space.

This can be a great element in our assembly. It will reduce down our trap assembly to a few elements.

Costs of the system are unknown of us as of now. However, we have noticed that it can be simply to

manufacture such a steam trap if we are given the chances and the necessary tools to do so.

Even though untested, we are sure that these technologies specified above can easily be

adjusted t our design. However, the main key is to determine whether they will be not only efficient and

useful to our conditions but also cost efficient. We will still look for better and yet simpler designs for

our assembly, and continue to improve its capacity.

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CONCLUSION

This semester, we have taken upon the task of designing a new steam trap assembly for our

senior design project. We have analyzed the design proposed by Con Edison, as a pedestal on which we

raise our design. For that, we have focused our analysis on the heat transfer, the stress analysis and the

fluid dynamics. This has allowed us to situate and improve our objective.

We have decided to choose this design for we have a common interest in steam production and

distribution. We also noted that it looked challenging. We expected a challenging problem to work on

because that will give us enough experience when it comes to engineering. At the same time, this

project does not only deal with High temperature and pressure but it also analyzes complex piping

structures. This is a good project in the sense it has allowed us to apply all the engineering knowledge

we have accumulated during our education.

As challenging it was, we had to face many frustrations in the sense where not a lot of literature

was available, literature that dealt with the mathematical analysis of steam trap assemblies. We have

gone through a lot of research and tutorials. We are glad that we have finally come to satisfying results.

We had hard time learning new software to realize a FEM analysis on the model. Plus, designing a new

model revealed to be harder than expected. We were restrained by the constraints specified earlier.

However, we have come to develop a more efficient design.

We are hoping to be able to develop an actual model of our assembly next semester and we are

expecting to be able to run it under normal conditions. Also, we will continue analyzing our design for

better performance. Analytical solutions will be implemented and we will continue searching for better,

cheaper and efficient technologies and ideas to implement in our design.

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REFERENCES

1. 2007 New York City steam explosion

http://en.wikipedia.org/wiki/2007_New_York_City_steam_explosion

2. Bill Harms, Water hammer in steam systems: cause and effect, “Mechanical Engineering”

3. Lucius Pitkin, Inc, Consulting Engineers, “July 18 2007 Steam Incident 41st Street and Lexington

Ave, New York, NY, Volume 1.

4. ABS Consulting, Risk Consulting Division, “July 18 2007 Steam Incident 41st Street and Lexington

Ave, New York, NY”

5. Con Edison Steam Operations, “Steam Operations: An overview”, Powerpoint presentation

6. Bevelhymer, Carl, “Steam”,

http://www.gothamgazette.com/article/issueoftheweek/20031110/200/674

7. Hicks Tyler G, Standard Handbook of Engineering Calculations, “Water Hammer Effects in Liquid

Pipelines”, page#3-282-383, McGraw Hill, Inc. 0-07028734-1 (ISBN), TA151H52 (CCNY Catalog).

8. Eshbach, Handbook of Engineering Fundamentals, Mechanics of Incompressible Fluid, “Water

Hammer”, page#627-628, Wiley Handbook Series, 0-47124553-4 (ISBN), TA151E8, 3rd edition.

9. Cengel Yunus A & Cimbala John A, Fluid Mechanics Fundamentals And Applications, 0-07-

247236-7 (ISBN)

10. Liu Cheng & Evett Jack B, Fundamentals of Fluid Mechanics, McGraw-Hills, Inc. 0-07-0197792

(ISBN).

11. Nayyar Mohinder L, Piping Handbook, “Stress Analysis of Piping System”, McGraw-Hill Inc. 0-07-

047106-1 (ISBN), 7th edition.

12. Avallone Eugene A, Sadegh Ali & Baumeister III Theodore, Mark’s Standard Handbook for

Mechanical Engineers, McGraw-Hill Inc. 0-07-004997-1 (ISBN), 11th edition.

13. "Selecting the right steam trap" by S.P. Frank, Richard Industries Inc.

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14. "User's view of steam traps" by Michael Lauber, PE/CEM Continental Tire North America

15. "Steam Traps Engineering Data Manual" Hoffman Specialty

16. Heat Transfer Essentials, Latif Jiji, 2nd Edition, 2002.

17. Acoustic sensors, www.netl.doe.gov. December 2008

18. Sensors technology, www.thomasnet.com.December 2008

19. Velan Valves, www.velansteamtraps.com. 2006.