CAISSON INTEGRITY MANAGEMENT - stork.com · 3 INTRODUCTION caisson integrity management Stork’s Caisson Integrity Management portfolio delivers an innovative service. Ensuring caissons,

1ASSET INTEGRITY PARTNER

Capability focus

CAISSONINTEGRITYMANAGEMENT

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CAPABILITY FOCUS:CONTENTS

caisson integrity management

03 Introduction

04 Assess, Inspect, Repair (AIR)

06 Industry Survey

07 Integrity Management Systems - Case study

INTEGRITY ASSESSMENT AND PLANNING 08 Assess (A)

10 Inspect (I)

13 Repair (R)

14 Contact details

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INTRODUCTION


Stork’s Caisson Integrity Management portfolio delivers an innovative service. Ensuring caissons, are fit-for-service we provide effective Inspection Management Programme ensuring reliability, technical integrity, safety and regulatory compliance is delivered. BACKGROUND AND INDUSTRY CHALLENGECaisson Integrity is a real issue for duty holders especially in a mature oil and gas market

as assets reach the end of their design life. A greater understanding of current integrity condition is needed to assure continued and safe operations. Stork have a rich history in Specialist Caisson Inspection and have combined an unrivalled service offering to provide a bespoke and complete caisson integrity management package, incorporating: Stork’s AIR philosophy of: ASSESS, INSPECT, REPAIR.

ADDEDVALUE

INTEGRITYENGINEERING & MANAGEMENT

INSPECTION SOLUTIONS

CATHODICPROTECTION SOLUTIONS

MONITORING SOLUTIONS

QUALITYSERVICES

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PROJECT MANAGEMENT

CONT

INUO

US IM

PROV

EMEN

T INNOVATION

COMMUNICATION

IDENTIFYCAISSON

FAILUREMECHANISM

LIKELIHOOD OF FAILURE

CONSEQUENCEOF FAILURE

KNOWNANOMALIES

RISKRANKING

INSPECTIONTYPE

INSPECTIONPLAN

INSPECTIONREPORTING

REPAIR & ANOMALY

MANAGEMENT

ASSESSINSPECT & REPAIR


Caisson integrity is seen as an important issue by most duty holders and the Health and Safety Executive (HSE) especially when considering the increased risk associated with ageing infrastructure. As greater emphasis is placed on asset life time extension, a general priority needs placed on having a consistent auditable and structured framework for managing caisson integrity.

Stork can assist in establishing an integrated Caisson Integrity Management framework designed to seamlessly integrate to a duty holder’s Structural Integrity Management (SIM) programme, ensuring it meets HSE Legislation

standards and also works in conjunction with an operator’s SIM programme, and relevant international standards. Stork delivers industry best practice to design a fit for purpose process for caisson integrity management. Stork has developed an all-encompassing service which is designed to:• assess risk• prioritise inspection• recommend inspection methods and frequency• enact inspection• recommend and project manage repair

methods where required An effective Caisson Integrity Management system is crucial and clear guidelines for Assess, Inspect and Repair procedures are imperative. This enables Caisson Structural Integrity to be maintained throughout a caissons life cycle:

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ASSESSINSPECT & REPAIR


Stork’s Inspection Management system can be implemented at any stage within a caissons life cycle. Ongoing assessments of Monitoring and Inspection data are an integral part of the future reliability and operational safety of each caisson.

By assessing and inspecting each caisson to understand its current condition and it’s interaction to interdependent Safety Critical Elements our inspection engineers can determine fitness for service and recommend prioritised inspect and repair options to extend the future life of each caisson.

BENEFITS A fully integrated approach to caisson integrity can deliver widespread benefits to an asset owner who is looking to establish a full understanding of caisson condition. This can be achieved by implementing a structured process of integrity management and enactment to assure continued safe operation. Stork’s experience in delivering a fully integrated package has delivered the following benefits:

• Single focal point, who manages all aspects of process from Risk Based Assesments (RBA) to repair, meaning reduced need for multiple contractors ensuring greater accountability and responsibility

• Continuity of service, with single company supporting all aspects of caisson management creating greater familiarity of client assets and processes throughout the delivery team

• Innovation commitment, utilising and developing the latest technology innovations to enhance caisson inspection data to allow for more informed decisions on remedial actions

• Optimised and planned inspection, and remedial programmes to ensure maximum cost efficiencies

• Multi-disciplined enactment teams, from one contractor ensuring Personal on Board(POB) is reduced where possible whilst delivering the highest quality standard

• Strong HSEQ culture, implemented throughout the process, ensuring safe working practices are adhered this includes the sharing of knowledge and experience with client project teams

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INDUSTRY SURVEY


In 2009 Stork carried out an industry survey with Duty holders to evaluate the various problems which are associated with caisson inspection and integrity management. The study covered 80 offshore platforms and approximately 200 pump, dump and carrier caissons.

The study identified typical failure mechnisms, how they affect different caissons, what current inspection techniques were used to identify areas of concern and pre-failure modes. A total of 29 reported anomalies were identified, across a variety of problems ranging from caissons being out of service to full replacement.

HIGHLIGHTS FROM THE STUDY INCLUDED:• Estimated cost for 29 reported incidents of £7

million• Internal corrosion identified as biggest threat to

caisson integrity • External inspection is most common inspection

technique• Typical monitoring frequency is around 3 years

per caisson• Recognised as significant issue amongst Duty

holders • Pump caissons have most potential failure modes

As part of the study the following recommendations were made by Stork:• Industry needs to recognise and rectify design

weaknesses which are resulting in design failures • Inspection, monitoring and mitigation needs to be

focused on detection and prevention of internal corrosion and marine fouling

• Need for engineering companies to develop improved technology

• Commitment required from Duty holders to adopt a proactive approach to inspection, monitoring and mitigation to avoid unplanned costs related to caisson integrity

Using our experience and knowledge Stork have designed a variety of specialist inspection tools alongside a bespoke caisson RBA methodology to ensure all degradation mechanisms can be captured and their risk mitigated where possible.

An integrated range of services including: RBA, specialist inspection tooling, specialist cleaning, cathodic protection and topside and subsea repair is available for clients recognising the importance of managing caisson integrity.

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CASE STUDY


In 2012, Stork was awarded an integrated caisson integrity management contract for a major North Sea operator which was the first of its kind in the industry. Throughout the first year the priority was to undertake a thorough review of the current condition of all 70 Caissons, using the client’s inspection history and design operational parameters. A detailed high level proposal for the inspection schemes was provided with a fully detailed RBI risk assessment for each caisson.

Once the frequency and type of inspection was defined Stork then supplied specialist equipment and personnel to deliver the inspection scopes recommended in the RBI assessment. Based on the inspection results, data is then incorporated into the RBI and inspection plans. In areas where anomalies were identified Stork have supported in repair workscopes using full repair and retrieval capabilities.

Stork produce annual reports that revisit the previous year’s reports, inspection data and strategies to confirm that they continue to reflect recommendations or changes in condition from the previous year.

CLIENT RESULTS & BENEFITS Stork through this ongoing successful partnership, has now developed with the client a caisson specific strategy and methodology which is seamlessly integrated within the duty holder’s structural integrity management framework.

Stork provides an integrity assessment of each caisson, delivering a live document of all caisson information from design, right through to previous inspection and repair history. Stork’s pro-active approach to caisson integrity management has provided the client with a clearer picture of overall caisson conditions, including what the main priorities are and what type of inspection and repair methods are required to ensure continued safe operation. This helps duty holders manage and plan scopes more efficiently and allows for effective prioritisation of resources.

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ASSESS (A)


Technical Integrity Assessment 2014 Doc No

Asset: Caisson: Use:

Summary Design Data Contents Diameter

(mm) Length

(m) Termination El. (m)

MAOP (barg)

Pump Type Flow rate

(m3/hr)

Wall thick (mm)

Termination Grill

Seawater 900 70.5 -45 1 SBWM 660 3 stage Electric

2300 25 and 35 in splash

zone

Yes

Summary Protection Data Coating

atmospheric Coating

Splashzone Coating Subsea

Coating Internal

CP Internal

CP External Internal Dosing

Monel Overlay

Painted Painted Painted None None Shared jacket CP Unknown No

Construction Details The seawater Pump A was installed in 1992 and is currently operational. The caisson is located on a horizontal tubular member spanning east to west between grid lines 3 and 4. The caisson is 70.500m long and terminates at EL-45.000m (termination grill attached) Supports at EL+6.000m, EL-15.000m and EL-40.000m. DWS is present at EL+22.30m. Internal access to the pump is can be obtained by removing the pump string. History from Inspection Scheme

Intake caissons incorporate pumps which may result in local corrosion and abrasion problems. In this case various factors such as dissimilar metal corrosion, oxygenated corrosion / erosion local to pump inlets and mechanical damage due to impacts between the caisson and pump could lead to significant internal caisson wall thinning.

ROV surveys have detected the presence of through wall perforation anomalies. Caisson C8 has 8 through wall corrosion locations on the south side between El -16m and El -19m with the pump housing visible. Caisson C10 has through wall corrosion on the west side at El -16m.

A strength analysis [20] was performed on the seawater intake caissons in 2005 between El -15m and El -16m with the aim of determining the maximum permissible wall thickness loss. The results showed that the minimum tolerable thickness for strength was 3.4mm.

The allowable stresses of API for cylinders under bending have been derived by using a factor of safety of 1.67 against the lower bound of the ultimate bending capacities. It is therefore valid to say that failure will occur at a wall thickness of < 3.1mm. It is recommended that inspections include wall thickness measurements to ensure integrity and for comparison with the above analysis.

In summary therefore, the inspection requirements for the seawater caissons and supports are as follows:

- GVI by ROV every two years for C8 and C10 and every three years for C9 and C11 to look for signs of corrosion, fatigue or other physical damage including loss of integrity of bolted connections or loss of integrity of the mechanical connectors.

- CP readings in conjunction with the ROV GVI every two years for C8 and C10 and every three years for C9 and C11.

- Wall thickness measurements at perforation elevations by external or internal means. -

Inspection History Topside 2008

- Inspections indicate that the topside of the caisson was in good condition 2007

- Internal Video - The dry section of the caisson was generally in good condition with some coating loss with light surface corrosion throughout

2006 - Internal Video - Blistering in coating and patches of coating loss were noted.

Inspection History Splashzone 2008

- Inspections indicate that the topside of the caisson was in good condition. 2007

- Internal Video - Showed bands of pitting with coating damage and light surface corrosion. Coating loss/pitting 360 degrees on circ. weld at –2.8m to –4.2m approx.

2006 - Internal Video - Patches of coating loss and sizeable pits were noted. Coating loss/pitting 360 degrees on

circ. weld at –2.8m to –4.2m approx. Inspection History Subsea 2014 Ultrasonic and Internal Visual Inspection: Decision on the 04072014 to locate swage with the top of the bottom of the liner located at 49.318m + 24m, with the liner top at 25.318m. Note: Datum taken from the top of the caisson flange connection. Areas of corrosion highlighted in STS report RP-8117-027255-14 Rev2. ‘Internal & Visual UT Inspection Report of SWLP C8. 2011

- A total of eight (8) perforations and one (1) area of 20+ perforations were found during this survey as detailed below. Along with this, several areas of pitting were observed. Corrosion evident at perforations. CP-PROX -976mV to -992mV.

Perforation L x W (mm) Distance below Guide at EL -15.3m (mm) 1 5 x 5 100 2 10 x 10 500 3 10 x 20 600 4 20 x 20 750 5 25 x 25 500 6 Area of 20 + Perforations (500 – 1000mm below EL -15.3m) 7 50 x 125 3000 8 60 x 60 2300 9 20 x 20 1800

2010

- TA Comment: RED - Last internal camera inspection in Jan 2007 indicated that corrosion had stabilised. Structural assessment

concluded that there was no threat to integrity in the short term provided corrosion remained stabilised. However the caisson section below the pump weighs 15 tonnes in water and is guided only. Therefore severance at pump level poses a significant dropped object hazard. Internal ultrasonic mapping should be carried out in the near future. This requires the pump to be pulled.

2007 - Internal Video - The subsea elements of the caisson was found to have 8 through wall corrosion locations on

the south side between EL-16.000m and EL-19.000m with the pump housing visible. Coating loss on circ. weld/pitting across 360 degrees of circ weld at –9.4m to –9.8m approx. Large patches of coating loss -12.9m to-13.1m and sizeable pits at -18.3m

2006 - Internal Video - The area between –15.9 wrt LAT and –19m wrt LAT, was exhibiting a host of through wall

anomalies ranging from relatively small 10x10mm perforations to larger more significant holes with relatively large craters. Large patches of extreme coating losses were also present. Sections with a number of large pits in and around the perforated areas were also present where the coating had been lost or

CAISSON INTEGRITY ASSESSMENTStork’s engineering team assessments are practical, cost effective and clearly communicated through a team of caisson specialists. A thorough review of key caisson information is the first step within the Stork Caisson Integrity Management process.

All relevant caisson information is initially collated and reviewed, forming the basis of a Caisson Integrity risk assessment:

A risk ranking assessment methodology for caisson review uses a number key data streams

from design data, inspection history, maintenance history, cathodic protection and anti-fouling anode replacement / dosing frequencies. This data is collated to determine a consequence and likelihood of caisson failure which is then combined to determine an overall risk for each caisson.

The methodology is based on existing offshore risk assessment recommended practice for pressure systems, adapted and made caisson specific based on years of experience. The method is robust and aids in ensuring that overall risk to Caisson Integrity remains As Low As Reasonably Practicable (ALARP).

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ASSESS (A)


The correct material deterioration and probability of failure assessment is essential for successful Caisson Integrity Management.

From Stork’s experience, potential failure threats often relate to the following deterioration mechanisms:• Atmospheric corrosion, a particular concern

around a splash zone• General corrosion by flowing seawater and/

or produced water• Localised internal corrosion from pump

impingement• Reduction of fatigue life by corrosion and cyclic

loading

INSPECTION PLANNINGThere is no “clear cut” guide which provides information on the exact type and frequency of inspections are required for caissons. API RP2A-LRFD recommends that topside members in the splash-zone are inspected annually by General Visual Inspection (GVI) and subsea member inspections should not have a frequency of more than 10 years. Due to the age of the installation, and the risks associated with caissons, experienced engineering judgment is applied when allocating inspection frequency and type. Once a full review has been undertaken Stork can issue clients a 10 year Inspection plan.

A risk Matrix is used to determine overall risk leading to a derived inspection frequency:

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INSPECT (I)


CAISSON INSPECTIONCaisson Inspection is a vital part of Stork’s Integrity Management system and the overall Inspection process. It is primarily concerned with preventing failure of the caissons by detecting early signs of possible future failure and taking action before the mechanism develops, leading to possible loss of Structural Integrity.

Stork is a leading Riser and Caisson Inspection contractor with over 20 years specific experience in deploying a number of Specialist Inspection techniques. Stork prides itself in listening to clients enabling a complete Inspection solution tailored to each client’s specific needs.

Stork is a market leader on Topside, Splash Zone and Subsea Caisson and Riser Inspections, committed

to innovation and finding solutions for challenging Inspection problems, which has been obtained through a well-developed and robust Inspection service, covering conventional and advanced Non-Destructive Testing (NDT) solutions. Our service includes the following in-house capabilities:

• Internal Remote Visual Inspection (RVI)• Internal Caisson Cleaning – High Pressure Water

Jet Cleaning (HPWJC)• Ultrasonic Wall Thickness Mapping • External Close Visual Inspection (CVI) and NDT

measurements by RAT • 3D Laser Mapping • Ex and Non Ex rated cameras including high

definition• Project Management of caisson repairs/

replacement using internal inspection techniques

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INSPECT (I)


REMOTE VISUAL INSPECTION (RVI)Remote visual inspections can be performed as a pre cursor to ultrasonic wall thickness mapping or as a standalone work scope. Remote visual inspection provides detailed information on the internal status of both the dry section and subsea section of the caisson while being performed safely from the top side. This can identify any significant features or gross defects within the caisson. Any defects observed can be sized and their orientation noted.

Remote visual inspection is also performed before and after high pressure water jetting to enable confirmation that this method is safe to proceed RVI is also undertaken to enable a more thorough inspection. Once all the scale and marine growth has been removed, which could have hidden anomalies from view in the pre jetting visual inspection.

HIGH PRESSURE WATER JET CLEANING (HPWJC) Stork’s in-house high pressure water jet cleaning service is utilised to clean the internal surface of the caisson. This is required for the preparation of the internals for the ultrasonic wall thickness mapping phase and also helps uncover any anomalies that were hidden with marine growth or scale.

This is a vital part of the overall scope and it is recommended to have a member of the inspection team present during this stage to ensure to sufficient surface prepartion to the correct standard.

ULTRASONIC WALL THICKNESS MAPPING Ultrasonic wall thickness mapping is performed to gather information on the remaining wall thickness of the caisson, areas are inspected where a couplant is present, this can help identify areas that have suffered wall loss and enable remedial action to be performed. This is to protect the caissons integrity and extend the life of the caisson.

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INSPECT (I)


3D LASER MAPPING The 3D laser profiler can be utilised to profile circumferential welds and heavy pitting where historically ultrasonic wall thickness mapping is unable to provide quantifiable readings, due to the surface profile causing signal deflection. It can also be used to size defects and provide a 3D model of any areas scanned. CAISSON CATHODIC PROTECTION Stork are Cathodic Protection (CP) specialists having 30 years’ experience and knowledge for both onshore and offshore assets. Stork’s knowledge base covers a vast and in depth range of services, Stork can provide a complete caisson CP system which can assist in protecting the pump string sections to provide protection to the caisson from microbially induced corrosion (MIC) and galvanic corrosion. Stork can survey, design, supply and project manage installation of a variety of CP systems including retrofitting CP sacrificial anodes. Stork also boast a new wireless CP system; Seatooth CP®, which is an innovative wireless communication CP monitoring system which allows each monitoring point to collect many years of data, rather than a single reading, during every inspection cycle. This can provide trending data on CP performance; allow communication through splash zone, enhanced data management and more efficient inspection and repair campaigns. BENEFITS• Accurate cathodic protection performance data• Extensive monitoring system life using rechargeable

power source technology• ROV friendly equipment for both fitting and data

recovery

• A variety of sensors including, coupons, temperature, conductivity, oxygen, and monitoring

• Permanently deployed sensors with no wet mate connectors

• Retrofit capability makes the system suitable for brownfield or greenfield

• Wireless data management with ROVs• Pre-configure sample rate to match condition

of anode• Battery life up to 15 years• Wireless recharge (optional) • Data through splash zone• Open architecture allows for additional sensor

inputs

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REPAIR (R)


REPAIR AND RETRIEVALDue to asset life extension, caissons have been in place longer than planned and most duty holders are facing deterioration. Repair methods have been key to maintaining Caissons in a safe, risk free condition.

Many caissons suffer corrosion damage overtime, in the Splash Zone or at uncoated welds. The corrosion weakens the caisson enough to require some kind of remedial action to stop the caisson from severance and falling onto pipelines or other seabed equipment, damaging structural members or the pump itself.

Stork’s project management and engineering services team are dedicated to assuring a safe and smoothly run repair scope. Our team can also effectively manage our third party repair specialists, leaving our client in safe hands, with one point of contact at all times.

The following repair techniques can be supported to rectify caisson integrity threats;

CAISSON SWAGE REPAIR Stork has experience in full project management and installation of internal liners to rehabilitate caissons;

which have lost structural strength in critical areas, where intervention is required in order to prevent caisson failure. Our combined service offering includes an initial survey or feasibility study, supply of internal liner material, connectors and associated components alongside the provision of in-house riggers, welders and inspection personnel working under an experienced project management team.

CAISSON COMPOSITE REPAIR Stork has a varied in-house composite repair portfolio including design, supply and installation both topside and subsea composite repairs to caisson components. Our engineers are fully trained in line with international standards organisation (ISO) 24817 and have a robust and practical process for calculation, design and application of our materials.

Stork’s AquaWrap and PowerSleeve, composite repair solutions, can be used topside and subsea dependent, on the application and can be used in conjunction with a variety of bespoke repair methods. Our range of tri-axial fibre-glass fabrics suite of epoxies can assist duty holders in reinstating both axial and hoop strength to caisson components in a cost and time efficient manner.

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RETRIEVAL (R)


FOR FURTHER INFORMATION, CONTACT: Greg IngramProduct Line Development Tel: +44 (0)1224 [email protected]

Steve RobbOperations Manager - Inspection ServicesTel: +44 (0)1224 [email protected]

RETRIEVAL Stork has extensive experience in designing bespoke retrieval tools for the retrieval of many kinds of dropped objects within caissons. Using our internal visual inspection cameras Stork can ensure that the correct retrieval tools are used for each application and the correct orientation is set to ensure successful retrieval and allowing continued safe operation with limited downtime.

Bespoke tools have been built to retrieve items such as:• Pump section• Anti-fouling anodes• Strainer Units• Scaffold Poles and Boards

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STORKNorfolk HousePitmedden RoadDyceAberdeen AB21 0DPUKTel: +44 (0)1224 722888Fax: +44 (0)1224 723406

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CAISSON INTEGRITY MANAGEMENT - stork.com · 3 INTRODUCTION caisson integrity management Stork’s Caisson Integrity Management portfolio delivers an innovative service. Ensuring caissons,