Pipe Repair Case Study

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

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Process Elements


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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

Presenter

Presentation Notes

Jonathan, This page really gives an overview of the project as opposed to background info. It probably isn’t required.


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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


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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.

Presenter

Presentation Notes

Routine inspection identified severe localised external corrosion and pitting on main oil export loading line. CAN was the contractor conducting the inspections; The pipe was deemed not fit for purpose; with an immediate repair or replacement required to continue operation. A repair was required to be carried out in the 5 – 7 day window between tanker loading operations when the line was not in use. Loss of availability of export loading line would of cost the operator approx. $160 million per month ≡ $40 million per week. Between Talisman and CAN deemed the line not fit for continued service.


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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.

Presenter

Presentation Notes

Incumbent maintenance contractor on site welded on a square patch over the external corrosion as an immediate repair. Client engaged DBL to perform FFS assessment on patch; Babcocks remit was to determine suitability of patch as a permanent repair, and if not permanent, how long the temporary repair would last (a service life) A level 3 FFS assessment was carried out, as to the patch over the corrosion did not permit use of normal corrosion defect assessment codes. # DBL contracted due to expertise, experience and accreditation on welded pipe systems.


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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

Presenter

Presentation Notes

Level 3 FFS required due to patch over corrosion Initial hand calculations performed because next tanker was due in and maximum working pressures for the pipeline had to be known. Hand calculations took only a couple of days and determined that the allowable working pressure of the line was below that of the design pressure limits (6.67 v 6.95 bar). A limit was set on the line pressure, which allowed continued operation. FEA subsequently, confirmed the findings of the hand calculations – took 2-3 weeks. Investigation and comparison against industry codes and guidelines also determined that the patch contravened the codes that determined a permanent 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

Presenter

Presentation Notes

FEA determined that the position of the patch between the supports would result in ‘pulling apart’ of patch. The defect was located on the lower face of the pipe and being exposed to the max bending loads. Don’t dwell on the technicalities of this bit however FFS determined that the line could be operated however at reduced flow and pressure rates


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Fitness For Service (FFS) Assessment – Conclusions

Presenter

Presentation Notes

Points here are: Important lesson here in operators must not only know the likely defect mechanisms of their plant, but have knowledge of the most appropriate repair techniques. There are very good codes and guidelines out there to assist you in choosing the right repair technique so the correct method can be employed from the start. However they give minimal guidance to the service life of a repair (ie whether a repair is permanent or temporary). This is where you need robust company procedures. Design of repairs on a case by case basis is time consuming and poses a production risk as if sections of plant have to be shutdown until repairs are compelte. This is where having your own robust internal company repair procedures which consider your specific plant and likely defect mechanisms in advance.


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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

Presenter

Presentation Notes

Following completion of DBs workscope to carry out FFS assessment of repair DBL were contracted to design, test, and install permanent repair. A consultation process was carried out between both parties to determine the most practical and safe solution which could be implemented in the timescale. DBL offered composite wraps (dismissed due to internal compliance rules – incidentally this has been subsequently changed following a review of the company repair procedure guidelines). DBL subsequently offered welded repair (encapsulation sleeve accepted as the right solution i.e. the patch would be surrounded by a sleeve which would be filled with a grout) The sleeve design differed from the patch design as a) distributed the stresses around the circumference, b) met the stipulations in all relevant design repair codes and guidelines. Due to the limited time available until tanker arrival, the removal of the existing patch and the installation of the subsequent repair was not feasible, therefore design was made to encapsulate the current temporary non-code compliant repair. DBL supplied full assurance engineering package to ensure code compliance Weld sleeve filled with grout to provide permanent protection against further corrosion, and to absorb load transfer between original pipe and new sleeve. Important point here is that it is beneficial to have a contractor who has not only knowledge of the integrity assessment but the practicalities of installing any repair. One stop shop companies are beneficial.


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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).

Presenter

Presentation Notes

Further to discussions with client around the 3 conditions in which the weld could take place (oil filled pipe/air filled pipe/water filled pipe), a water filled pipe was accepted as the safest condition. Also, the oil-water-oil change out gave just enough time to do the work required before the arrival of the next tanker. Due to the high heat sink involved in welding onto a water filled line, and the resulting problems in obtaining pre-heat this causes, A mock up was created to carry out the weld procedure. This not only qualified the weld procedure but also the same welders were used that were going to be used on site.


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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

Presenter

Presentation Notes

Bespoke callipers manufactured by DBL to provide precise dimensions of pipe (pipe found to be non-circular – Oval).


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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


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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

Pipe Repair Case Study

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