UTILITIES DISTRIBUTION EXPANSIVE FORCES STEAM SESSION 11 J. MICHAEL CARSON PE

Transcription

1 UTILITIES DISTRIBUTION EXPANSIVE FORCES STEAM SESSION 11 J. MICHAEL CARSON PE 1

2 What motivated this session We saw a need to discuss to steam start-up and cool down expansive forces We could find nothing discussing it We decided to do it ourselves by passing on three lessons learned to the next generation

3 1.0 Introduction 2.0 Phase change 3.0 Expansion 4.0 Rapid start-up Agenda

4 1.0 Introduction 2.0 Phase change 3.0 Expansion 4.0 Rapid start-up Agenda

5 The next picture is you on every shut down and start up

6 May The Force Be With You

7 May The Force Be With You Huge forces are created by: Expansion & contraction Vaporization & condensation How huge can the force be?

8 Some will say Myth-Busters debunked this Others will say Myth-Busters debunked their debunking of this It doesn t matter because what is the point being made?

9 Your choice: 1. Overlook (or ignore) the force and suffer the consequences 2. Treat the force with respect and control the results

10 1.0 Introduction 2.0 Phase change 3.0 Expansion 4.0 Rapid start-up Agenda

11 Stewart Center Line #1 Buried 18, 125 psi main

12 Line #1 Buried 18, 125 psi main Steam flow is from south to north Stewart Center

13 Line #1 Buried 18, 125 psi main Steam flow is from south to north But system is looped Steam can flow from north to south Stewart Center

14 Stewart Center 75 ft 160 ft Pit-F, a confined space, has an E-J, & anchored elbow Anchored elbow Pit-E, a confined space, has a trapped E-J

15 Pit-K has a trapped expansion joint 450 ft Pit-G has a double expansion joint 425 ft 75 ft Stewart Center 1110 ft between drip traps Pit-F, a confined space, has an E-J, & anchored elbow Anchored elbow 160 ft Pit-E, a confined space, has a trapped E-J

16 December 7, 2015 Wade Power Plant has a perfect storm of issues, lost power, steam flow stopped Distribution pipe temperatures dropped to about 230 F As the steam pressure was being restored boiler water levels were erratic Occasionally a slug of water blocked the distribution pipes, pressure would fluctuate, dropping low (even down to 0 psig) and back up quickly Let s review the start-up

17 Pit-E & Pit-F are confined spaces so were unmanned during start-up

18 Pit-E & Pit-F are confined spaces so were unmanned during start-up State Street Pit is not a confined space and was manned

19 Warm-up started about 7:30 AM Through the morning steam pressure rose but water slugging problems caused frequent pressure fluctuations No distribution issues were reported Everything seemed fine until about 11:30 OMG what that big bang? After the dust settled (literally) this is what we found in Pit-F

20 Let s look at the end of the beam See any problems with this elbow? This was the original shape of the I-beam

21 The force twisted the beam and bent the steel plate And broke the weld

22 And broke the weld What the bare pipe looked like

23 And dimpled the pipe (even with the additional plate welded on) And broke this weld What do you think was the cause? Our analysis

24 230 F 0 psig 7:30 AM Pipe & insulation about 230 F Pressure 0 psig The distance from Pit-F to the boilers Gauge Pressure (psig) Saturated Steam Temp ( F)

25 Pit-F 7:30 AM Pipe & insulation about 230 F Pressure 0 psig How long will it take start-up steam pressure and temperature to travel approximately 3000 feet of pipe? It will take hours Gauge Pressure (psig) Saturated Steam Temp ( F) Wade Power Plant

26 230 F 0 psig 7:30 AM Pipe & insulation about 230 F Pressure 0 psig 7:30 to 10:30 AM Steam is flowing (with fits and starts) But steam pressure & temp not yet traveled to Pit-F At this point what effect will pressure fluctuation have on the system in these pits? Gauge Pressure (psig) Saturated Steam Temp ( F)

27 Steam 20 PSIG 7:30 AM Pipe & insulation about 230 F Pressure 0 psig 7:30 to 10:30 AM Steam is flowing (with fits and starts) But it takes hours for steam pressure & temp to travel to Pit-F 11:00 AM Steam is flowing to Pit-F about 20 psig Steam is about 260 F Gauge Pressure (psig) Saturated Steam Temp ( F)

28 Steam 20 PSIG Condensate 260 F 7:30 AM Pipe & insulation about 230 F Pressure 0 psig 7:30 to 10:30 AM Steam is flowing (with fits and starts) But it takes hours for steam pressure & temp to travel to Pit-F 11:00 AM Steam is flowing to Pit-F about 20 psig Steam is about 260 F Significant warm-up condensate Gauge Pressure Anyone remember how far between drip traps? (psig) Saturated Steam Temp ( F)

29 Steam 20 PSIG Condensate 260 F Using an on-line calculator - over 2000 lbs of condensate How much would you guess is left in the pipe? 7:30 AM Pipe & insulation about 230 F Pressure 0 psig 7:30 to 10:30 AM Steam is flowing (with fits and starts) But it takes hours for steam pressure & temp to travel to Pit-F 11:00 AM Steam is flowing to Pit-F about 20 psig Steam is about 260 F Significant warm-up condensate Gauge Pressure (psig) Saturated Steam Temp ( F) Anyone remember how far between drip traps?

30 Condensate 260 F Suddenly the pressure drops What will happen to all those hundreds of pounds of hot condensate? Gauge Pressure (psig) Saturated Steam Temp ( F)

31 Suddenly the pressure drops The piping absorbs the expansion Immediately the pressure from the plant spikes back up Gauge Pressure (psig) Saturated Steam Temp ( F)

32 Suddenly the pressure drops The piping absorbs the expansion Immediately the pressure spikes back up Slugs of condensate are pulled in by the condensing steam Gauge Pressure (psig) Saturated Steam Temp ( F)

33 What is the take-away

34 1. Uncontrolled pressure change can cause a state change and large potentially damaging forces

35 Agenda 1.0 Introduction 2.0 Phase change 3.0 Expansion 4.0 Rapid start-up In an earlier session we calculated the expansion/contraction forces

36 F This heated pipe is anchored at both ends How much force is produced? T ( F) 200 Diameter (inches) Force (lbs f ) 292, , ,800 1,072,300 1,274,600 1,751, ,900 1,096,000 1,695,500 2,144,600 2,549,200 3,502,400

37 F This heated pipe is anchored at both ends How much force is produced? Where does the force go? Let s see that force in an LP line in Civil Engineering Force (lbs f ) 292, , ,800 1,072,300 1,274,600 1,751, ,900 1,096,000 1,695,500 2,144,600 2,549,200 3,502,400

38 Let s zoom in

39 The bare pipe Anchor used to be vertical Anchor dug into the base here And pulled away from the base here

40 Using expansion to our advantage in Pit-C The pipe used to be straight

41 North Buried 18 dia 125 psi

42 385 ft Pit B Anchored on north side Pit C Three ball joints & anchored on north side Let s see how these ball joints work

43 Anchor Each joint can bend about 15 degrees The force required to make a ball joint move

44 About 6 ft 20,000 ft-lbs torque 18 Dia. 125 psig steam 125 Typical Ball Joint Torque Chart

45 6 ft = Over 3300 lb f required to start joint movement 20,000 ft-lbs 3300 lb f

46 Anchor 3300 lb f is no problem because there is an anchor on the north side And an expanding pipe can produce 100 s of thousands of pounds of force 3300 lb f Watch as this pipe expands

47 385 ft 330 ft Pit B Anchored on north side Pit C Three ball joints & anchored on north side Pit D Double slip-joint Let s see how a double slip-joint works

48 Expansion Operational force > 1000 lbs per inch of pipe dia. 18 dia. Means > 18,000 lb f Expansion

49 385 ft 330 ft 3300 lb f

50 385 ft 330 ft 3300 lb f 18,000 lb f For the discussion assume Installed at 50 F Operating superheated steam is 550 F At 500 F steel will expand: 3.15 per 100

51 385 ft 330 ft 3300 lb f 18,000 lb f 12 Expansion 10 Expansion

52 This anchor broke We had a mechanical failure

53 All the expansion went south! 3300 lb f 18,000 lb f Since the ball joints take 3300 lb f to move And the slip joint takes 18,000 lb f to move

54 Expansion The ball joints took all the expansion, and got pushed up against the wall Expansion

55 This extended outage would cause a major campus disruption So what did we do? Traditional repair method is to shut off the line, dig up and repair the anchor, and reset the expansion joints

56 Reinforced the south side of Pit D

57

58 Installed a framework on the south inside wall of Pit D

59

60 Installed a similar system on the north side of Pit C

61 In the evening we moved these nuts tight to the steel

62 Then we allowed the steam to approach saturation What was the superheat temperature? 550 F Back to the steam table From this point the pipe cannot pull south In the evening we moved these nuts tight to the steel

63 330 Feet Pressure Sat Temp (psig) ( F) What is the temperature for saturated 125 psi steam? 353 F 550 F What T did the pipe see? T = 200 F Steel expands and contracts about 0.75 per 100 per 100 F

64 330 Feet How much will the pipe move? As the pipe cools it contracts about 5 T = 200 F Steel expands and contracts about 0.75 per 100 per 100 F

65 Pulling the ball joints to the north As the pipe cools it contracts about 5

66 As the pipe heated it expanded Pushing the pipe into the slip joint The pipe was In the morning we moved these nuts tight anchored here to the steel and ran the steam superheated

67 Every night we walked the pipe to the north until the slip joint and the ball joints were positioned properly then We rebuilt the anchor

68 The second lesson learned

69 1. Uncontrolled pressure change can cause a state change and large potentially damaging forces 2. Uncontrolled temperature change can cause uncontrolled expansion and large potentially damaging forces

70 1.0 Introduction 2.0 Phase change 3.0 Expansion 4.0 Rapid start-up Agenda

71 Why do we have to start-up so slow? Can t we speed it up and go home at a normal time? Cooling down or warming up rapidly will have unintended consequences Especially at the anchors

72 System has been off for a while, everything is at ambient temperature of 70 F Guide Trap Saddle

73 Open the valve

74 450 F 450 F 450 F 450 F Steam What will this cause? The top temperature overtakes the bottom temperature Condensate about 350 F

75 Have you ever seen this? Inconsequential or worrisome?

76 What if there is an obstruction? What about draining the condensate?

77 What problems could this guide have?

78 What problems could this slip joint have? It could be a double slip joint

79 The anchor is designed for balanced forces Expansive Force Expansive Force 450 F Steam

80 Expansive Force With an unbalanced load what problems do you see? The anchor is designed for balanced forces It could be an anchored elbow Expansive Force 450 F Steam

81 Anchors are designed for balanced forces Expansive Force Expansive Force

82 What possible problem do you see? Expansive Force

83 Uncontrolled expansion and contraction can cause another hidden problem That came to the world s attention by a railway accident

84 1842, public celebration honoring king Louis Philippe I in the Gardens of Versailles

85 Many returned to Paris by train An axle snapped, the train derailed, scattering the fire-box contents What made the axle snap? Catastrophic metal fatigue Let s discuss this

86 Metal Fatigue Fatigue: the weakening of a material caused by repeated loading and unloading If the loads are above a certain threshold, microscopic cracks will begin to form Eventually a crack will reach a critical size and the structure will fracture

87 Metal Fatigue Fatigue is the weakening of a material caused by repeated loading and unloading If the loads are above a certain threshold, microscopic cracks will begin to form Eventually a crack will reach a critical size, the crack will propagate suddenly, and the structure will fracture Do steam pipes ever get loads above a certain threshold? They can if expansion is uncontrolled

88 Investigation into the Failure of a Steam Pipe Line Bend N.J.Jooste Inspection Engineer SCI Inspection Authority Sasolburg, South Africa niekie.jooste@sasol.com Keywords: Failure Investigation; Case Study; Corrosion Fatigue; Steam Pipe Line; Bending Stresses Abstract This article is an investigation into the failure of a bend in a (30 psig) steam pipe line. It was concluded that the failure was due to a corrosion fatigue mechanism. The fatigue originated from the expansion and contraction of the steam line, which would result in bending stresses in the pipe bend.

89 Investigation into the Failure of a Steam Pipe Line Bend N.J.Jooste Inspection Engineer SCI Inspection Authority Sasolburg, South Africa niekie.jooste@sasol.com Keywords: Failure Investigation; Case Study; Corrosion Fatigue; Steam Pipe Line; Bending Stresses Abstract This article is an investigation into the failure of a bend in a (30 psig) steam pipe line. It was concluded that the failure was due to a corrosion fatigue mechanism. The fatigue originated from the expansion and contraction of the steam line, which would result in bending stresses in the pipe bend. The take-away from this discussion

90 1. Uncontrolled pressure change can cause a state change and large potentially damaging forces 2. Uncontrolled temperature change can cause uncontrolled expansion and large potentially damaging forces 3. Rapid start-up can cause pipes to bind, damaging components, and may cause metal fatigue in the pipe or anchors

91 Thank you QUESTIONS? Mike Carson (765) EOE/AA