Technical Consultancy Services. Forensic Engineering and Expert Witness. ERA Technology Limited

Transcription

1 ERA Technology Limited Technical Consultancy Services Forensic Engineering and Expert Witness Claire Malpas Rotating Equipment Consultant

2 Agenda About ERA Introduction to Failure Investigations Case Study 1 Reciprocating Compressor Case Study 2 Gas Turbine How to make an investigation easier 2

3 About ERA Technology Responsive, independent engineering consultancy Engaged by many of top 100 international organisations Impressive engineering knowledge drawn from origins in research and development World-class engineers and specialists Offices in UK, Europe and UAE global network through sister companies Part of the Global providers of technical, quality and safety solutions to the Energy industries

4 Specialist asset experience We have particular knowledge of the following assets: Turbo-machinery gas and steam turbines Engines Pumps Rotating Compressors Motors Transformers Cables Switchgear Electrical Protection devices Fired Heaters & Steam Reformers Coke Drums, Platformer reactors vessels & pipework Static Heat Exchangers, pressure equipment & boilers 4

5 Through-life services Safety Engineering Power Systems Design EMC Conceptual Design Detailed Design System Specification FEED, EPC Contractors Engineering Design Improvements 3 rd Party Verification Power Systems Protection Procurement Construction Commissioning Construction Companies Engineering Subcontractors Remaining Life Assessments Fitness for Service Forensic Engineering and Root Cause Analysis Through-Life Management Change of Use/Life Extension/End of Life Decommissioning Owner Operators Specialist Contractors 5

6 Why carry out a failure investigation? Insurers & Loss Adjusters: Understanding the root causes Separating out damage by event Identifying the limits of attributable damage Assisting during re-instatement Operators & Owners: Understanding the root causes Identifying corrective actions to avoid recurrence Assisting during re-instatement E.g. Liaising with suppliers, evaluating feasibility Confirming effectiveness of corrective actions Improve safety 6

7 First steps in a failure investigation Collect the initial information Examine the damage As soon as possible after the event In-situ if possible Witness dismantling if possible Obtain evidence Damaged components in their as-found condition Interview witnesses Data and records 7

8 Typical investigation techniques Physical examination of components Simulation e.g. FEA, calculations, metallography Brainstorming sessions Cause-effect mapping (Apollo approach) Elimination of unlikely causes Building hypothesis Testing hypothesis 8

9 Case Study 1 Fool me once 9

10 Case Study Fool me once Upstream Oil and Gas field in Africa Commissioning of a 2 stage reciprocating booster compressor system Catastrophic failure hydrocarbon leak Following rebuild the unit failed again on start-up Parties Involved Owner/operator Package provider Compressor OEM Third party independent ERA Technology 10

11 Case Study Reciprocating compressors Process diagram/conditions Initial information from the failures Findings Recommendations Outcomes 11

12 Reciprocating Compressors Positive displacement Fixed volume Does not like incompressible fluid Can be run by diesel engines, electric motors, or turbines Used where high pressure ratios are required, e.g. for export of dry natural gas or instrument air etc. 12

13 Process Diagram 13

14 Process Diagram Scrubber For liquid removal Compressor Aftercooler To main compressor Ultra low pressure gas in Low pressure gas in 14

15 Process Conditions 0.3 bar 4 bar 12 bar To main compressor 20 MMSCFD 10 MMSCFD LP gas in ULP gas in 15

16 1 st failure During a commissioning test run the system tripped on hydrocarbon release in the area of the compressor. On inspection the cylinder head had come apart from the body. The unit was stripped and lots of damage found. Vibration monitoring had been faulty so did not trip the unit at the first sign of damage. The owners and contractors concluded it had been built incorrectly. Rebuilt the unit with a high level of precision and supervision. 16

17 Piston damage 17

18 2 nd Failure During a test run the system tripped, on high vibration on the compressor cylinder no 5. The cylinder was stripped and damage was found to the piston. 18

19 Areas of investigation Manufacture of the piston Assembly of the compressor Design of the package Operating conditions Start up procedure 19

20 Piston plug manufacture Threads of the remaining plugs were sectioned and examined Identified a varied quality of plug engagement Force would still be required to remove the plug from the piston Identified the direction of force was inward to the cylinder 20

21 Assembly of compressors The owners/operators suspected the assembly of the unit as the cause of the first failure Rebuild was conducted under strict supervision All stages of build signed off by qualified personnel No indications of poor build issues following 2 nd failure 21

22 Design of the package Package design from a reputable company All equipment conforms to industry standards One discrepancy from owners standards Layout appears similar to comparable packages However on discussion with the package provider there was some confusion over the specification relating to the operating conditions 22

23 Operating conditions Specification called for 0 20MMscfd Originally designed for exactly 20MMscfd Recycle line added to the package design as an afterthought Actual flow ~5MMscfd through stage 1 and 10MMscfd through stage 2 Recycle always used Leads to lower temperatures, higher liquid knock out extra work for the scrubber Liquid carry over as a cause? Liquid in the compressor could cause the high pressure required to knock in the plug However, although it wasn t designed for these conditions, the scrubber is able to cope with the calculated amount of additional liquid knock out. 23

24 Start-up procedure Start up 24

25 Process Conditions - design 0.3 bar 4 bar 12 bar To main compressor 20 MMSCFD 10 MMSCFD ULP gas in 0.3barg LP gas in 4barg 25

26 Process Conditions during start up 4 bar 12 bar 36 bar To main compressor 20 MMSCFD 10 MMSCFD ULP gas in 0.3barg LP gas in 4barg 26

27 Outlet of 1 st stage 2 nd stage recycle 1 st stage recycle LP gas in 27

28 As built 1 st stage recycle LP gas in 2 nd stage recycle 28

29 Knock on effects Is the scrubber able to cope? No, not with these conditions Liquid will build up in the scrubber and carry over to the cylinder Incompressible liquid will cause very high forces on the face of the piston 29

30 Root cause of the failure High pressures at start up combined with recycling the gas at low temperatures increases the liquid to be separated in the scrubber. Scrubber cannot handle this volume of liquid so some carries over to the cylinder. The liquid carry over is likely to be the cause of the force on the plug causing the damage and release of the piston plugs. Poor plug thread engagement is a contributing factor. 30

31 Recommendations Improved QA on the threads of the pistons and plugs would reduce the chance of a piston with a weak engagement from entering service. Reconfigure the cylinder from double acting to single acting reducing the volume flow from 20MMscfd to 10MMscfd. Review start up procedure to stop high pressures building in the system which is currently causing high liquid drop out in the second stage at start up. 31

32 Outcomes Liability shift from owner/build contractor to OEM and package designer Financial settlement for the owner Rebuild according to the recommended changes Successful commissioning and operation Flexibility to reinstate the double acting compressor if flow rate increases 32

33 Learning points Worthwhile carrying out a technical RCA Cause of failure different to first thought Could have avoided the second failure Justification for attributing liability Improvements to quality procedures reduce the risk of reoccurrence 33

34 Case Study 2 Where s the damage? 34

35 Case study Where s the damage? Gas turbine is operated in a Mediterranean environment Used for power generation Condition monitoring contract with the OEM Surge protection tripped machine following control card failure Operator found that performance changed Waterwashing did not help Operator suspected mechanical damage Operator committed to investigation and repair costs, then called insurer 35

36 Case Study Gas turbine power loss Causes of power loss Areas for investigation Physical damage Control system Environment Findings Learning points 36

37 Power (MW) Power output 44 Expected loss within 8,000 hours up to 2% Stall Event Lease unit Jun 09-Sep 18-Dec 28-Mar 06-Jul 14-Oct 22-Jan 02-May 10-Aug Date 37

38 No sign of physical damage Unit was stripped at the OEM facility No evidence of significant damage to cause a power loss So where is the power loss coming from? Data from the turbine was provided, but very limited One data point per day 38

39 What can affect power output? Common causes: Outside temperature, pressure, humidity Dirty filters Dirt build up on the compressor blades Increased clearances (wear and tear or damage) Maintenance reports do not suggest this Waterwashed regularly, no sign of this at strip Nothing significant found at strip Other causes: Change of fuel calorific value Fogging / inlet cooling Steam/water injection Gas turbine tuning No fuel change No change No change No control system changes 39

40 An ISO day Temperatures onsite range from ~ 10 C to 35 C in the year Power output in previous year MW, Need to correct for ambient conditions to make a comparison ISO standard day: kpa 15 C 60% humidity 40

41 Corrected Turbine Performance Linear performance No signs of significant loss Speed limited in later months What is limiting the power? 41

42 Gas Turbine limits Speed control Temperature control Turbine normally limiting on temperature Detailed data not available for analysis Only average temperature and spread Condition monitoring reports reviewed 42

43 Spread (degc) Spread data T48 Spread Before Stall After Stall Jun 09-Sep 18-Dec 28-Mar 06-Jul 14-Oct 22-Jan 02-May 10-Aug Date 43

44 Exhaust thermocouple behaviour 44

45 Summary of findings No evidence of physical damage to the gas path Power reduction rather than power loss Speed limited by maximum limit on average exhaust temperature Probable failure of one probe Power reduction unrelated to stall event Cause of problem found in the condition monitoring report OEM did not highlight issue Repair work carried out was unnecessary 45

46 Lessons learned Good understanding of gas turbine operation beneficial OEM reports should be read and not just filed Rushing to initiate repair work can lead to unnecessary work/cost Recording data can help to solve future investigations 46

47 How to make an investigation easier Leave scene untouched as long as possible Retain or quarantine all components for analysis Record data for high value assets such as gas turbines Involve all parties as soon as possible Conduct witness interviews early Open and honest communication Have all parties attend the investigation together Do not rush to conclusions! 47

48 Questions? 48