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Condensate Induced Water Hammer in a Steam Distribution System- Results in Fatality

H. L. Debban L. E. Eyre

RECEWED MAR 1 2 1Y96 .

O S T I Date Published

February 1996

Presentid at: Utility Business Operations in the 90s Palo Alto, CA February 21-23, 1996

Pre ared for the U.S. De artment of Energy

Waste Management 0fft)Ce of Environmental i estoration and

DISCLM-2.CHP (1-91)

LEGAL DISCLAIMEB This repolt was prepared as an account of work sponsored by an agemy of the United States Government. Neither the United Stater Government nor any ageacy thereof, nor any of their cmploycei, nor any of their contncton, subcontractors or their employees, makes any warranty, express or implied, or assumes any legd liability or responsibility for the accuracy, completenets, or any third party's use or the results of such use of any information, apparatus, product, or p m e u disclosed, or represents that itr usc would not infringe privately owned rights. Reference herein to any specific commercial product, pmts s , or service by trade name, trademark, manufactureq orkthenvise, does not necessarily cohnit~te or imply its endorsement, rccommendation, or favoring by he United S f ~ t e s Government or any agency thereof or its contractors or subcontractors. .The views and opinions of authors expressed herein do not necessarily m~te or reflect thost of the United States Government or any agency thereof.

This report has been rcproduccd from the best available copy.

Rintcd in the United Stater of America

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CONDENSATE INDUCED WATER HAMMER IN A STEAM DISTRIBUTION SYSTEM RESULTS IN A FATALITY

Herb L. Debban Larry E. Eyre

ICF KAISER HANFORD COMPANY RICHLAND, WASHINGTON

ABSTRACT

Water hammer events in steam distribution piping interrupt service and have the potential t o cause serious injury and property damage. condensation induced water hammer are discussed and recommendations aimed t o

Conditions of

improve safety of steam systems are presented. Condensate hammer events at Hanford, a DOE facility, are examined.

Key words: STEAM PIPING, CONDENSATE, WATER HAMMER, SAFETY RECOMMENDATIONS.

induced water

PRINCIPLE,

INTRODUCTION

The Hanford Site covers 560 square miles along the Columbia River in southeastern Washington State. in 1943, Hanford's primary mission for 45 years was t o produce plutonium for national defense. the region was recognized. Hanford's major facilities and halted plutonium production.

Developed by the federal government beginning

In the mid 1960's the need for economic diversification of The end of the Cold War brought the shutdown of

Today, Hanford's mission is focused on three mission elements: Site cleanup, science and technology, and economic diversification. These mission elements directly align with three of the five business areas defined in the Secretary of Energy's Strategic P1 an -- Environmental Quality, Science and Technology, and Industri a1 Competitiveness.

To accomplish the missions, both past and present, the Hanford Site utilizes several steam distribution networks with miles of piping.

Steam distribution networks used at Hanford are similar t o those used in many cities, government facilities and private institutions t o distribute centrally generated steam for heating, cooling and process use. these systems are safe, efficient means of distributing energy. certain circumstances, this energy can be amplified by water hammer t o exceed the strength of the piping system. Condensate induced water hammer, commonly called a steam explosion by the media, can result in fatalities t o workers or t o the public and can.result in significant property damage.

Typically, condensation induced water hammer occurs when steam is introduced into a pipe that is partially filled with condensate. induced water hammer can occur when 1 arge quantities o f sub-cooled condensate

In normal operation But, under

However, condensate

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is rapidly introduced i n t o a steam f i l l e d section o f piping. An accident of this type took place on June 7, 1993 a t Hanford, Washington, and resulted i n one f a t a l i t y and interrupted steam service t o several c r i t i c a l process faci 1 i t ies.

June 7. 1993 Accident

On June 7, 1993, a t about 7:00pm, a Westinghouse Hanford Company Journeyman Power Operator received c r i t i ca l steam burns and lung injuries while opening an 8-inch main steam l ine isolation valve, MSS-25, (see f igure 1) i n the steam valve (U-3) p i t i n the 300 Area of the Department of Energy Hanford S i te . The U-3 p i t i s a par t of a process steam supply system using steam a t about 350 degrees fahrenheit and 120 psi.

Conditions i n the steam system included a large quantity of condensate (approximately 1500 gal lons) backed up iri a 840-foot run o f the main steamline between valve MSS-25, which is the lowest point i n the system and the next isolat ion valve. The condensate was f a i r l y cool since t h i s portion o f the piping system is underground and had been inactive for 8 months. Steam was on the downstream side of MSS-25 w i t h a functioning steam t r ap i n this section o f the l ine . flow t o the 331 building. The operator entered the p i t , unlocked and opened the 8 inch isolat ion valve, MSS-25. Indicators are tha t he opened the valve over 50 percent i n 1 t o 2 minutes. Condensate rushed into the steam f i l l e d downstream p i p i n g , f i l l i n g the vertical leg and when su f f i c i en t quantity had entered the next upper horizontal section a water hammer ensued. i n i t i a t ed a severe thermal-hydraul i c t ransient , result ing i: a condensate induced water hammer with pressures up t o about 2300 l b f / i n i n the p i t p i p i n g . i ron , blind flanged isolation valve i n the upper section o f the p i t . ' The rupture created an instantaneous release o f h i g h pressure water and steam i n t o the p i t .

The operator exited the p i t on his own, s ta t ing tha t he was burned. one week l a t e r , due t o , his burns and l u n g damage.

An investigation board was convened t o determine casual fac tors and make recommendations t o preclude accidents o f this type. These recommendations resulted i n an action plan.

The upstream side o f the valve was also pressurized t o allow steam

T h i s

The t ransient was terminated quickly by a rupture o f a 6-inch cas t

He died

ACTION PLAN STRATEGY

A very detailed plan provided the direction for developing and completing the actions necessary t o correct Hanford's steam system operations.

Four areas o f weakness were c i ted i n the accident investigation report and were addressed i n the plan:

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1.

2.

3.

4 .

Conduct of Operations - make a s tep change i n the way the steam plants are operated.

Technical - evaluate the overall steam system design, es tabl ish effect ive configuration management program, es tabl ish a steam system in-service inspection program, provide as-buil t drawings and a labeling program and develop a system f o r operating a l l steam valves i n pits remotely.

an

Safety Standards and implementations - establ ish a safety program t o ensure a safe workplace environment is provided t o the employees and visitors.

Personnel Training - improve t ra ining i n the recognition o f condensate induced water hammer and other hazards. t ra ining program tha t addresses rapid isolat ion i n the event o f a steam l ine or component rupture.

Establish a

A project manager was established t o ensure effective implementation of this plan. benchmark other f a c i l i t i e s t o identify best practices, oversee the conduct of t ra ining fo r operations and maintenance personnel as well as evaluating the technical safety reviews.

Responsibilities, other t h a n organize and manage resources, were t o

A laboratory analysis was conducted t o identify the causes and provide visual indication o f condensate induced water hammer. pipes, i n various configurations, enabling the viewers t o actually see the e f f ec t of f i l l i n g a pipe w i t h water in the presence o f steam. A video of this laboratory analysis was made and is used i n the condensate induced water hammer t ra ining program. Additionally, the t ra ining incorporated a "steam board," a tab le t o p working model using glass pipes and steam traps. Operators could now "see" what was actually happening i n re la t ion t o the sounds they were hearing w i t h a stethoscope o r the from temperature readings from a hand held pyrometer.

T h i s analysis uti1 ized glass

A WAKE UP CALL

Significant accomplishments were made i n implementing the action plan. However, on June, 16, 1994 (one year a f t e r the f a t a l i t y ) , another condensate induced water hammer was experienced a t Hanford. A t a s i te , 20 miles North of the previous water hammer, during a steam restoration evolution a t the 284E powerhouse a condensate induced water hammer occurred when the operators began t o "crack open" the main 12" limitorque valve (see Figure Z), which would i n i t i a t e steam flow and begin the heat up process. A horizontal section of piping from the road r i s e r , up t o the East general limitorque valve, f i l l e d w i t h condensate, during a two week outage. Approximately 700 gallons o f condensate collected i n the pipe. No personnel were injured, b u t moderate damage was sustained by the p i p i n g s u p p o r t s and three elbows on the 12" steam line exceeding t h e i r yield s t ress . Also, a 12" f lex gasket fa i led due t o

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st ressing of ,he flange b o l t s , breaking system i n t and steam t o be discharged.

gr i ty , which ca d water

When the limitorque valve was cracked open, condensate, under steam pressure of 225 psig, flowed i n t o the powerhouse piping system. lower horizontal section decreased t o create a void between the condensate surface and the t o p of the p i p e steam flowed into this space and s e t up the condition fo r the condensate induced water hammer, which las ted between 5-6 minutes.

When the level i n the

Investigation l a t e r revealed t h a t the condensate b u i l d up was due t o a 15 psi t r ap being ins ta l led i n the 225 psi system. discharge condensate in this condition.

The t r a p could n o t function t o

During the course of the investigation o f this event, i t became painfully obvious t h a t the previous actions were n o t effect ive i n communicating the cause and means of correcting condensate*-induced water hammer. The focus on correcting the conditions f o r a condensate induced water hammer became fuzzy i n the hundreds o f action items. Fortunately, a core of experts had emerged from the year long ef for t and were able t o identify the action plan shor t f a l l . Training, as a r e su l t of the 1993 incident, led personnel t o believe t h a t slow operation would prevent water hammers. The corrective action plan had placed s ignif icant emphasis on be t te r control of the operation o f valves and components. hammer severity does not decrease w i t h slow valve operation.

Laboratory simulations had shown tha t condensate induced water

From these events we learned tha t we must improve our communication of the causes and corrective actions t o prevent condensate induced water hammer.

LESSONS LEARNED

A comparison o f t h e 1993 and 1994 events validated tha t substantial progress had been made, b u t there was much l e f t t o do. Additionally, i t was recognized t h a t the focus on preventing water hammer needed t o be regained and redirected. Specifically:

1. A c lear , understandable safety principle was developed along w i t h th i r teen (13) recommendations fo r preventing condensate induced water hammer. T h i s principle provides the cornerstone f o r t ra in ing , procedures and hazard analysis. The safety pr inciple s t a t e s , “Do not mix steam w i t h water, e i t h e r by i n j e c t i n g water i n t o a steam system o r steam i n t o a system con ta in ing water . Steam and water cannot be mixed s a f e l y i n a p i p i n g system w i t h o u t r i s k i n g the occurrence o f Condensate Induced Water Hammer. Condensate shou7d be assumed t o be i n a77 low p o i n t s and dead legs u n t i l proven otherwise.” (see Figure 3)

Revitalized the t ra ining program, placing par t icu lar emphasis on: 2.

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Assuring understanding of the safety principle of water hammer, recommended safe operations, and design practices. The training was given t o all personnel who interface with steam, not just the operators. We increased the use o f hands-on sessions to increase practical experience. We are insistent upon obtaining assurance that the training has been successfully learned.

The training emphasized’that there is no safe way t o introduce steam flow into or from a pressurized system containing any significant amount of condensate. The only safe action is t o depressurize and drain the system, then control the warm up and slow pressurization of the piping whi 1 e removing condensate vi a drains, bl owdowns, and traps.

3. Developed and use a standard steam procedure guide t o ensure basic lessons learned and the safety principles are incorporated into f aci 1 i ty procedures.

4.

5.

Developed a means of identifying non-routine operations and specified actions to take for serious risklfrequency levels.

Conducted an inspection to ensure that the correct steam traps are installed in existing systems and improved systems t o assure that correct traps continue t o be installed.

6. Continued t o place significant emphasis on Conduct of Operations, particularly in the areas of preplanning and recognition of abnormal indications.

CONCLUSION

Condensation Induced Water Hammer is fatally serious and is preventable in piping systems if designers and operators understand and apply the safety principle and the 13 recommendations.

The Safety Principle is an effective cornerstone in preventing condensate induced water hammer. I t effectively ties training, design, planning, procedure development and management oversight into an integrated approach t o steam system safety. Hundreds of successful, safe steam evolutions have validated its effectiveness.

Steam Valve Pit U-3

Steam Trap Vent /

. 10 in.Thick Walls

\ 8 in. Line from Manhole #l (15 in. Corrugated Conduit)

\

FIGURE 1 .

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FIGURE 2

CONDENSATE INDUCED WATER HAMMER

1

2

3

4

5

6

7

8

9

10

11

12

13

SAFETY PRINCIPLE - ~~

STEAM AND WATER CANNOT BE SAFELY MIXED IN A PIPING SYSTEM WTHOUT RISKING

CONDENSATE INDUCED WATER HAMMER. DO NOT MIX STEAM WITH WATER EITHER BY INJECTING

WATER INTO A STEAM SYSTEM OR STEAM INTO A SYSTEM THAT INCLUDES WATER (CONDENSATE).

CONDENSATE SHOULD BE ASSUMED TO BE IN ALL LOW P0INTS.AND DEAD LEGS UNTIL PROVEN

OTHERWISE.

RECOMMENDATIONS Review and inspect a11 steam sysrems to ensure proper distribution and sizing of cold traps for startup, and operation, and that a11 low points have steam traps. Give maintenance the highest priority. Frequently inspect all steam traps to ensure that they operate properly and that no condensate accumulates. Immediately repair or repIace erratic steam traps. U s e thermocoupIes where feasible to locate condensate accumulation. Do not u s e the method of "CRACKING OPEN" the vaIve to avoid condensation induced water hammer. This will not guarantee safe operation. The formation of a condensation induced water sIug can occur at very low Condensate flow conditions.

VaIves in pipe lines which lack properly positioned steam traps should remain open at all times or preferably should be removed from the piping system.

Before opening vaIves in steam lines, check for adequate pIacement of steam traps. Verify that the steam traps can operate properly, and fuIIy open the bleed valves, using a reduced system pressure to remove any remaining condensates..

Where feasible operate the valves remotely using mechanical extension linkage, reach rods, or adequately controllable power operated valves.

Inspect the piping system for sagging, where necessary install steam traps or repair the sagging. Check and repair the piping insuIation, it will save energy and reduce the ac'cumuIation of condensate in the piping system.

Activation of cold steam piping shouId be performed slowly at reduced pressure and with trap bleed valves continuously open. The above list of recommendations should be followed regardless of piping size. Do not exclude small pipe sizes without an appropriate anaIysis. All isolation valves are to have bypass systems. However, bypass operation will not prevent water hammer if condensate is present. PIacement of blowdown'valves before and after a vertical rise (such as over- theroad) is required to prevent possible condensate accumulation.

XmproperIy designed steam/water systems shouId not have the incorrect features overcome by operational methods. The systems must have the incorrect features corrected.

FIGURE 3 - I