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pipe repair
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Piping Repair Case Study
48” Loading Line Permanent Welded Repair
Jonathan Brindley - Doosan Babcock
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48” Loading Line - Permanent Welded Repair
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Presentation Objectives Demonstrate that a total solution delivered from one contractor for integrity management through to implementation makes sense Educate that robust repair procedures save time, money, and mitigate risk
Project Management
1 2 3 4 5 6
Process Elements
48” Loading Line - Permanent Welded Repair
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Overview Doosan Babcock approached by North Sea Oil and Gas Exploration and
Production company to assess a site repair.
Engineering investigation determined the repair could only be classed as ‘temporary’
Alternative repair options presented.
Client selected welded sleeve repair.
Full EPC service provided by Doosan Babcock – Sleeve design Weld procedure development Site implementation
48” Loading Line - Permanent Welded Repair
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Location Storage and Processing Terminal. Nominal Oil Process Capacity 375,000
Standard Barrels per Day
Oil storage capacity of 3.5m Barrels Oil exported via single point mooring or jetty
Export Jetty Line: Export Capacity: 80,000
Barrels per Hour
Responsible for over 40% of UK crude exports
48” Loading Line - Permanent Welded Repair
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External Corrosion: Routine inspection identified severe localised
external corrosion and pitting on main oil export loading line.
The pipe was not fit for purpose; with an immediate repair or replacement required to continue operation.
Loss of availability of export loading line would of
cost the operator approx. $160 million per month ≡ $40 million per week.
48” Loading Line - Permanent Welded Repair
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Immediate Requirement It was not possible to descale the worst
affected area due to the risk of a break in containment. A fillet welded patch was installed to contain the worst affected area.
A review of the repair was carried out to assess
suitability of use on other areas of corrosion.
Doosan Babcock contracted due to expertise and experience of working with pipework system issues and knowledge of current repair codes and guidelines.
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Assessment of pre-existing patch repairs and areas of external wall thinning
Stress analysis carried out using traditional hand calculations
and finite element analysis (FEA). Hand calculations allowed maximum working pressures to be specified while FEA was undertaken.
FFS Assessment utilised relevant codes, standards and guidelines: – API579-1 / ASME FFS 2007 Fitness For Service (American
Petroleum Institute) – PD5500:2006 Specification for Unfired Fusion Welded Pressure
Vessels (British Standards Institute) – ASME B31.3 Process Piping Design (American Society of
Mechanical Engineers) – ASME PCC-2 Repair of Pressure Equipment & Piping – OTO 038/2001 Temporary/permanent pipe repair – Guidelines
(Health & Safety Executive)
1. Fitness For Service (FFS) Assessment
48” Loading Line - Permanent Welded Repair
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By studying the deformed shape of a patched pipe it is seen that the patch causes a localised stiffening effect to the shape of the pipe. This localised stiffening, in addition to the bending moments resulting from the pipe and contents weight, causes the pipe to distort it in such a way to induce tension in the root of the weld.
Maximum working pressure of loading line limited due to
welded patch repair. Repair codes do not recommend patch repairs for ‘general’
wall loss only ‘localised making fillet welded patched unsuitable for other defect areas.
Fitness For Service (FFS) Assessment – Conclusions
48” Loading Line - Permanent Welded Repair
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Fitness For Service (FFS) Assessment – Conclusions
48” Loading Line - Permanent Welded Repair
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Welded and composite repair options investigated and presented to client.
Full encapsulation sleeve repairs with injected grout filler chosen as most appropriate repair – Sleeve designed in accordance with substrate
design code ASME B31.3 Repair designed in accordance with guidance in
ASME PCC-2-2006 (Repair of Pressure Equipment & Piping).
Full assurance engineering package provided to
client: – Static Stress Analysis of client pipe with addition
of repair sleeve weight. – Fatigue assessment due to cyclic operation of
loading line. – Buckling load calculations (Determine maximum
sleeve annulus integrity pressure test). – Brittle fracture assessment.
2. Permanent Repair Design & Assurance Engineering
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3 & 4. Weld Procedure Development & Qualification Tools
Plant Integrity Technology
Risk assessment determined safest condition for welding sleeve to substrate was with loading line water filled – no flow condition.
Weld Procedure Specifications (WPS) provided by Doosan Babcock Welding Engineers
Weld designed with minimal pre-heat and no post-weld heat treatment required due to large internal volume of water at ambient temperature.
Supplementary assurance testing in line with API 1104 Appendix B – In Service Welding developed to support weld Procedure Qualification Report (PQR).
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Bespoke measurement instrumentation manufactured to capture outer diameter (OD) and pipe ovality information during site survey.
Each sleeve bespoke manufactured by Service Technology fabricators utilising site survey information to minimise fitting time on site. Sleeves designed to encompass existing patch repairs.
Doosan Babcock Construction department provided site implementation team: – Welding Supervisor – Fitting Supervisor – Welders – Pipe Fitters
Sleeve welds non-destructively examined, sleeve annulus pressure tested then injected with polymeric grout to complete repair.
5 & 6. Sleeve Fabrication & Site Implementation
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Presentation Conclusions A total solution delivered from one contractor for integrity management through to implementation makes sense Robust repair procedures save time, money, and mitigate risk
Project Management
1 2 3 4 5 6
Process Elements
48” Loading Line - Permanent Welded Repair
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Customer Feedback
“…the design and assessment work you carried out for us was significant in achieving this end and we look forward to working with you in future on these and other types of projects.”
–UK Operational Integrity Manager “…and agree that this has been a significant piece of work completed within the schedule and within estimates. A large effort has been put into the design work, project organisation and site implementation with no accidents or incidents. Many thanks.”
–Onshore Operation Co-ordinator
A final thought from HSE Research Report RR509: Plant Ageing: Management of Equipment Containing Hazardous Fluids or Pressure
“Temporary repairs are often a source of trouble, they may very easily become permanent even if not suitable for long term service. There is also a risk that such repairs are done in a hurry, without full assessment of implications.”
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Questions