Module 5 Pipeline repairs.pdf

Pipeline Operations and Integrity Management Module 5 Pipeline Repairs

 Alan Murray 2017

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Outline

 Where are we? we?

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Pipeline repair topics

• Safety considerations • Types of defects to repair • Pipeline repair methods • Regulatory Regulatory and an d code requirements

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REPAIR: Rule 1… Safety First! •

Safety is always our first consideration.

 –

Pressure reductions, excavation safety, trench safety, welding safety, pipe movement safety, fire prevention, emergency procedures, etc., are our primary concerns.

 –

Pressure reductions alone may not be sufficient to demonstrate safety prior to working on a pipeline.

•

Some pipelines may have ‘locked-in’ stresses; for example, from ground movement (onshore) or a buckle (offshore).

•

These locked-in stresses need to considered prior to work on the line .

Use recognised, proven procedures, and qualified personnel, and make use of relevant standards e.g. API RP 2200. 4

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REPAIR: Rule 2… Caution •

Some wise words on repair*:

 – ‘Do no harm!’ • A bad repair can make matters worse.

• Repairs need careful engineering, at least as much as a new construction.

• Do not act in haste.

 – A repair is often not a good time to try something new. • There is less experience with a new procedure, compared to tried and tested designs. Surprises may occur with uncertainty and incompletely planned engineering.

REPAIR: Rule 3… For life!

❖

Remember*… a good repair approach/philosophy is: ❖

Replace ‘like-for-like’.

❖

 Apply a ‘temporary’ repair, until replacement can be carried out.

❖

 Apply a ‘permanent’ repair, only where replacement is not practical.

Repair 

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Pipeline Repairs

• • •

The concept of repairing a pipe presumes that an injurious defect is present. The purpose of a repair is to restore the full serviceability of the pipe permanently, although temporary repairs may sometimes be necessary. Safety before, during, and after the repair operation is the first priority.

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How Repair Situations Arise

▪ A leak is discovered ▪ Excavator reports or is observed hitting the pipe

▪ An anomaly identified by in-line inspection is confirmed in the field

▪ Excavation for another purpose reveals a repairable condition

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Terminology ▪ Anomaly – A condition or possible imperfection that appears to be different from normal pipe ▪ Flaw – A confirmed imperfection that is not injurious to the pipe ▪ Defect – A confirmed imperfection that is injurious to the pipe ▪ Discovery – Occurs when enough is known to determine that an anomaly or condition presents a threat to the pipe integrity Al

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Terminology

• Leak – A defect that permits the pipe contents to escape but that does not render the pipe inoperable • Rupture – A sudden, unstable, and rapid propagation of a crack or opening emanating from a defect

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Terminology ▪ Maximum Operating Pressure, MOP – The

maximum level of steady-state pressure permitted by the pipeline-design criteria, the federal regulations, or the company’s operating procedure, whichever is less. ▪ Discovery Pressure – the pressure level

existing at the location of the anomaly at the time it is discovered or reported.

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Terminology • Historical Pressure – A pressure level that is known to have existed at the location of the anomaly after the anomaly was present in its current state. •For a gas pipeline, no pressure level may be considered a historical level if it occurred more than 1 year (365 days) prior to the discovery of the anomaly. •For a liquid pipeline, no pressure level may be considered a historical level if it occurred more than 60 days prior to the discovery of the anomaly. • A previous hydrostatic test pressure can be used as a historical pressure level if it meets the time requirements.

• Repair Pressure – The pressure level at the location of the anomaly to be repaired at the time the repair is carried out. Al

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SAFETY CONSIDERATIONS

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Safety Issues

• Pressure reduction • Excavation safety • Trench safety • Welding on a live pipeline

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Safety is the first consideration ▪ A defect could be on the verge of failure ▪ Lowering the pressure may be necessary ▪ Prevent excavation damage to the pipe ▪ Observe trench safety requirements ▪ Observe fire-prevention standards ▪ Use qualified maintenance personnel ▪ Use qualified repair procedures ▪ Observe live-line welding requirements ▪ Inspect the repair during and after installation

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Factors to Consider ▪ Pipe Material: Diameter, thickness, grade, seam ▪ ▪ ▪ ▪

type, chemistry, toughness Operating Characteristics: Maximum operating pressure, type of product, flow rate Location: Terrain, accessibility, proximity to population Special Circumstances: Leaking or not, brittle pipe, high built-in stress, couplings or acetylene welds Nature and extent of the anomaly

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Reduction pressure reduction is considered • A Pressure appropriate where uncertainty  exists that an anomaly is safe at the operating pressure. This is particularly true at the time of excavation, as a matter of worker safety.

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PRESSURE REDUCTIONS: Why reduce pressure? •

We need to reduce pressure to a safe level before repair, due to:

 – LEAKING PRODUCT. If pipe is ruptured or the defect is leaking, we need to make the pipe and surrounding safe.

 – REPAIR: We may need to plan future pressure reductions depending on type of repair/rehabilitation.

Images from Clock Spring Literature www.clocksprong.com

• Some composite repairs require pressure reductions of 50%. 18

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PRESSURE REDUCTIONS: Why reduce pressure? •

We need to reduce pressure to a safe level before repair, due to:

 – LEAKING PRODUCT.

 – REPAIR.  – RECOATING: Recoating may require removal of pipe from trench, and pressure may be required to be reduced to zero.

In situ coating com pleted

REGULATIONS: Some regulations require pressure reductions is a pipeline is to be moved; e.g. regulations in USA require pressure to be reduced to 50% of the MOP in a liquid pipeline, if it is to be moved.

PRESSURE REDUCTIONS: Operational Experience Minor releases are sometimes recorded during excavation (e.g. during grit blasting the pipeline), but casualties are very rare. However, there are recorded failures of pipelines during excavation of known defects, and these failures have resulted in fatalities*. Because of this risk, companies do reduce pressure.

Image courtesy of Marianella Ojeda, Promigas, Colombia

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PRESSURE REDUCTIONS: Why reduce pressure for non-leaking defects? Pressure reduction is needed in a damaged pipe because: Pipeline damage can fail when held at constant pressure (‘time dependent effects’)*. Pipeline pressure is never constant, and can increase above the MOP, e.g. due to overpressures (‘operational effects’).

Load

Load

Load

Load

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PRESSURE REDUCTIONS: Examples of Pressure Reductions We have two types of guidance for pressure reductions that relate to the ‘severity’ of damage:

 ALL DAMAGE

SEVERE DAMAGE If the defect is very severe (e.g. very long (with a risk of rupture), or very deep (>80%wt), or a crack)

- For pipe wall defects, lower operating pressure to 80% of that at which defect was discovered/inflicted, until defect has been assessed. For structural defects (e.g. buckling) structural assessments will be needed. ’80%’*

- The pipeline pressure should be reduced to the lower of 80% of the pressure at which the defect was inflicted/discovered, or a hoop stress level of 30% SMYS ’30% SMYS’

Pressure should be controlled. Overpressures not allowed. These stress levels can be waived if a risk analysis shows it to be safe to do so 22

Pressure Reduction Policy Reduce pressure when: ▪ A defect is discovered unexpectedly, unless it is obviously a superficial flaw ▪ An ILI anomaly is categorized as  “Immediate Repair Condition”  ▪ When excavating other ILI anomaly categories and uncertainty exists as to its nature or severity ▪ In the event of known or suspected mechanical damage Al

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Pressure Reduction Policy Reduce pressure level to: ▪ The calculated safe operating pressure for the anomaly, or ▪ 80% of recent maximum pressure level

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API RP 2200 ▪ Personnel

▪ Qualified oversight (supervisor, team leader) ▪ Repair personnel should not only be trained but briefed about issues specific to a particular repair ▪ Careful planning is essential

▪ Training and equipment

▪ Lockout/tagout procedures ▪ Confined space ▪ Worker’s right-to-know ▪ Personal protective equipment ▪ Fire prevention and protection ▪ Emergency response training ▪ Atmospheric testing devices

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API RP 2200 • •

Job Planning details • Applicable laws and regulations • Permits • Adjacent utilities • One-Call • Traffic control • Limit public access • Shut-down procedures • Safety-related condition • Drain-down/purging • Tools and equipment • Brief personnel • Material safety data sheet • Maintain communication regarding pressure and flow

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Shut-down procedures Leak/rupture spill/flammability hazard Combustible gas indicator Toxicity testing Check confined space (trench) for oxygen Safe trenching practices Support and secure pipe Confirm wall thickness with UT Turn off, lock, tag rectifiers Electrically bond separation points Cold cut unless area made safe Monitor atmosphere Use vapor seals and plugs

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Pop Quiz True or false?

• An anomaly is injurious to the pipe______ • A flaw in the pipe requires a repair______ • A pressure reduction during the repair process is recommended______

• A pressure reduction of 10% may be appropriate______

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REPAIRABLE PIPELINE DEFECTS

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Types of defects

• Corrosion (internal, external) • Stress-corrosion cracking • Long seam defects • Girth weld defects • Dents and mechanical damage • Metallurgical features • Construction damage • Damage from natural events Al

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External corrosion

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Internal corrosion

Microbe-induced corrosion

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Selective corrosion on girth welds

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Stress-corrosion cracking (SCC)

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Lamination affected by hydrogen blister and cracking

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ERW Pipe Defects

Cold Bond (LF only)

Hook Cracks (LF or HF ERW)

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DSAW Pipe Defects Hot Cracks

Offset Beads

Shipment Fatigue Al

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Typical mechanical damage Al

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Typical mechanical damage Note creases in pipe wall (left); cracking, and crushed microstructure (below).

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NDE of mechanical damage Probably a waste of time on gouges in as-found condition. No gouges should be left in pipe operating at high stress levels in untreated condition. Grind damage out first, then do NDE.

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Typical damage from poor padding during construction

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Puncture caused by sharp rock under pipe

SCC in rock dent

Pressure-cycle induced fatigue in rerounded dent (following removal of rock)

Coating disbondment and corrosion in rock dent Al

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Damage from seismic survey shot adjacent to pipe. Discovered by ILI.

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Lightning damage

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Dresser coupling construction

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Buckles caused during construction Ripples in field bend

Onshore line

Offshore line Al

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Buckles due to soil movement

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Girth welds affected by soil movement Al

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Some Common Welding Defects

Slag Inclusions

Hollow Bead (Porosity) Incomplete Penetration (IP) Al

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Some Common Welding Defects Hydrogen-Induced Cracking (HIC), High-Low, and Excess Penetration

External Undercut, Slag Inclusions, and High-Low Al

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REPAIRS

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Selection factors

• Codes, standards, regulations • Company policies • Effectiveness in situation • Impact on service • Feasibility and availability • Cost and convenience • Training, quality, NDE Al

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Types of Repair • Pipe replacement • Surface grinding • Steel sleeves

• • • •

• Reinforcement • Pressure containment • Compression type • Grout-filled • Expanded

Nonmetallic Mechanical Hot tap and fitting Welding Al

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WELDED SLEEVE REPAIR* ❖

The ‘welded sleeve’ is a very popular repair method.

It is used as a permanent repair method for many types of damage. ❖

It involves welding* together two ‘half shells’ around the damaged pipeline, to form a ‘sleeve’. ❖

Two Half shells

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Type A and Type B Sleeves •

Defect filled with hardenable material

•

Steel half shells closely fitted around the defect area

•

Joined by longitudinal welds

•

Ends not welded (Type A) or welded (Type B)

•

Type B sleeves designed to be pressure containing

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WELDED SLEEVE REPAIR The welded sleeve involves welding* together two ‘half shells’ around the damaged pipeline, to form a ‘sleeve’. ❖

See API RP 1107 and API STD 1104 for guidance on their application. ❖

Sleeve

Half shell

Half shell

Half shell

Pipeline (damage under sleeve) 55

Non-pressure containing sleeves: • side seams groove or fillet welds • end gaps sealed to keep out water

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Pressure-containing: • side seam must use groove butt welds • welding procedures for end fillets must be suitable for pipe metallurgy and cooling rates

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How reinforcing sleeves work ▪ Reinforcing sleeves take up negligible hoop stress (15%). They restore strength of pipe by restraining bulging at defect.

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WELDED SLEEVE: Effectiveness Research at AGA showed these sleeves (‘Type B’ – see later) can strengthen damaged pipe up to a failure stress of 100% SMYS. Test on 200mm long, 80% wall thickness defect

Welded sleeve on 762mm diameter, 17.5mm, X65 pipe, before test

Welded sleeve did not fail at >30MPa. Note bulging of line pipe 59

WELDED SLEEVE: Principles of operation Most welded sleeves increase the failure pressure of a damaged pipe by: ‘stress sharing’ between the sleeve and the damage pipe; and, restraint of pipe ‘bulging’.

The next slides explain these benefits in more detail.

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WELDED SLEEVE: Principles of operation (1) STRESS SHARING: If the welded sleeve fits around the pipeline perfectly, there is ‘stress sharing’ – the stress in the carrier pipe is reduced. If this sleeve is of a similar thickness to the carrier pipe, and applied at a pressure of Pr , and the pipeline pressure is then increased to Po, the sleeve shares the increases in stress from P o to Pr . Thicker sleeves take higher stresses. Any carelessness in fitting will result in poor stress sharing. 2. DEFECT IS 1. LOAD IS TRANSFERRED

RESTRAINED

DEFECT

REPAIR SHELL

PIPELINE

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WELDED SLEEVE: Principles of operation (2) RESTRAINT OF BULGING :The sleeves stop a defect from ‘bulging’ in the ductile line pipe.

Defects in pressurised pipe bulge outwards prior to failure. If this bulging is prevented or restricted, the failure is prevented. 2. DEFECT IS RESTRAINED

1. LOAD IS TRANSFERRED

REPAIR SHELL

DEFECT

PIPELINE

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Methods for achieving tight fitup between sleeve and pipe

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Use of filler materials

▪ Effectiveness of repair is improved by close fitup, fill of annular spaces, and pressure reduction during installation.

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Use of filler materials Hardenable filler materials • Polyester epoxy (e.g. auto body filler or purpose made resins) • Work time affected by mix, temperatures • Apply sleeve prior to cure and squeeze out excess filler, or • Allow to harden first then shape the contour by grinding

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TYPE B SLEEVE*: Close fit and fill •

A Type B sleeve needs to be a ‘close fit’, so grind off weld reinforcements at DSAW welds and girth welds.

•

Filling the annulus with hardenable materials is good practice (removes any corrosive environment, helps ‘close fit’, and prevents internal pressure within the annulus)***.

Fill ***’Repair of Pressure Equipment and Piping’, ASME PCC-2-2006. January, 2007, and ASME B31.8 Section 851.42.

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Comments About Sleeves ▪ For Type A, sleeve wall and grade need not match ▪ ▪ ▪

carrier pipe or meet Barlow equation to be effective. For Type B, sleeve integrity relies on seam weld quality. Type B sleeves thicker than the pipe should be edge tapered to the wall thickness Tapping thru sleeve and pipe removes hoop stress from pipe. Not recommended where not absolutely necessary (taps vulnerable to damage, sleeve becomes pressure component).

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Edge treatment on sleeves ▪ Unlike the fillet welds on socket welding fittings or

flange hubs, the fillet weld on the end of a repair sleeve is not structural, even if it is intended to contain pressure. ▪ In order to avoid excessive stress concentration, the fillet weld should be no larger than 1.0t, rather than 1.4t. ▪ If the sleeve is heavier than the pipe, it should be tapered to nominally 1.0t. ▪  Any gap on fit-up should be added to the fillet leg dimension. Al

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Poor fit-up and lack of penetration in seam weld adversely affects reliability of pressure-containing sleeves.

Repair sleeve seam consisting of cap welded over bar stock 

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Other sleeve configurations Dresser 110 – For repair of girth welds

Dresser 220 – For repair of couplings

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Sleeves on pipeline bends

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Epoxy groutfilled shell repair sleeve

•No in-service welding •Annular space accommodates deformations

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Compression repair sleeve ▪ Concept involves heating the sleeve at the

time of installation ▪ Clamp in place and weld side bar ▪ Involves no welding to the pipeline ▪ Thermal contraction upon cooling creates an interference fit with the pipeline ▪ This relieves hoop stress in the pipe due to internal pressure

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Compression repair sleeve

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Compression repair sleeve Installation quality verified by measuring amount of shrinkage after cooling

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Mechanical clamps

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Special enclosures for leaking flanges

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Mechanical clamps

• Versatile • Involves no welding (though some can be welded to make permanent seal)

• Can accommodate out-of-round pipe • Usually considered “temporary” • Large sizes are expensive • Large sizes are very heavy Al

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Grinding out mechanical damage in dents ▪ Metal loss caused by gouging is worse than metal loss caused by corrosion due to surface damage, cracks, indentation

▪ Mechanical damage can be converted to ordinary metal loss by removing the damaged metal

▪ Demonstrated by testing and service experience Al

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Effectiveness of grind repair -- test data

Restoration of pressure capacity

Improvement of fatigue life Al

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Grinding out mechanical damage in dents Grind out gouge to smooth contour, to max depth of 40% of wall over limited to length as follows:

1/ 2

    g / t     L  (1.25Dt )    1   1.1g / t  1        2

Ref: CSA Z662 and “Repair of Pipeline Dents Containing Minor Scratches” J.F. Kiefner and C.R. Alexander, PRCI L51788, 3/18/99

Damage repaired by grinding

Inspection by PT and UT verified removal of any cracks and adequate remaining wall. Al

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Nonmetallic composite wrap repair

▪ Polymer matrix reinforced by oriented strand or woven fabric

▪ May be preformed to shape or hand laidup wet

▪ Chemically bonded to pipe and between layers, cured in place

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Composite Repairs • Wide range of products now available • Composite sleeves are typically cured offsite, then attached to the pipe with adhesives; other composite repairs are cured on site. • Most work by keeping a defect from bulging. So, the defect needs to be filled with hardenable material. • Can carry some (not a lot) hoop stresses depending on installation procedure. • Generally does NOT carry axial loads 85

Composite wrap repairs 1. Apply Filler

Clockspring® composite wrap repair

2. Apply  Adhesive

5. Coat and Backfill

3. Wrap

4. Tighten Al

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COMPOSITE REINFORCEMENT SLEEVES •

Fibreglass re-inforced composite material wrapped around the pipe can restore pipeline strength in the hoop direction.

•

Composites can have 10x the strength of a steel, and 25% of the weight and can have wide-ranging applications**.

•

They follow the contour of the pipe/damage.

•

They are light and easy to handle.

•

No pipeline ‘hot work’ is required.

‘ClockspringTM’

Usually defect is first filled with high compressive strength filler material 87

COMPOSITE REINFORCEMENT SLEEVES •

All composite repair systems on pipelines employ*: •

some type of fibre system that provides strength and stiffness (typically glass or carbon fibres);

•

a resin matrix used to transfer load between fibres; and in the case of ‘layered’ systems;

•

an adhesive that is used to bond layers.

*C Alexander, ‘Repairing Damaged Pipelines’, Pipeline and Gas Technology, March 2008

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COMPOSITE SLEEVES: Caution •

Composite strength tensile strength) and stiffness (elastic modulus) can diminish with time.  –

•

The materials must be tested for long term properties.

No ‘hot’ work needed on line:  –

but adhesive used has a limited working time;

 –

and repair may need several hours of curing, before the pipeline can be backfilled.

Image from Wrapmaster Literature Video courtesy of Craig Hall, GEPII

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COMPOSITE SLEEVES: Caution •

There are now many types of composite sleeve.  –

Use recognised methods**: •

What is the effect of pressure at time of installation?

•

Effect of cyclic pressures?

•

Effect of surface preparation?

•

Repair of mechanical damage?

•

Etc.

Images from Clock Spring Literature www.clocksprong.com

Usually defect is first filled with high compressive strength filler material

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COMPOSITE SLEEVES: Caution •

Care should be exercised:  –

they are not specifically designed to resist bending or axial stresses;

 –

some wraps do not alter MFL indications, so cannot be detected by pigs;

 –

technicians need to be trained to apply the repairs.

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TD Williamson Black-Diamond® CF composite wrap repair

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WrapMaster PermaWrap® composite wrap repair

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Armor Plate® composite wrap repair

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Permabond® polyurethane sealantfilled encapsulation system for leaking couplings

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The original composite wrap repair Al

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Composite wrap repairs

• Composite wrap concept extensively tested • Lightweight and does not corrode • In-service welding not required • Requires marking to show up on ILI or thorough records of installations

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Composite wrap repairs ▪ Effectiveness is a function of stiffness, not strength. Most products are effective, but not all demonstrate equal performance.

▪ Suitable for ordinary non-leaking corrosion or other flaws that have been converted by grinding to blunt metal loss free of cracks.

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Composite wrap repairs ▪ Low modulus of composite is incapable of limiting strains in the steel pipe.

▪ Not suitable for:

▪ mechanical damage untreated by grinding ▪ LF-ERW seam defects ▪ selective corrosion strain-sensitive defects or any situation involving ▪ strain-sensitive brittle material behavior

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Hot tapping

• Hot tap may be used to remove a defect smaller than the tap

• Full-size stopple stopple may be used to isolate pipeline section for replacing pipe without interruption of service

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Hot tapping

(Shown: Standard Valve used when tapping to install lateral lines.

3. A TDW Tapping Machine is Machine  is installed on the fitting, and SANDWICH® Valve the valve is opened. After Option allows pilot drill penetrates, the temporary plugging tapping machine fills with operation.) product, and air is purged from the housing. The tap is 1. A fitting is permanently secured make through the line and the coupon is retained. retained . to the line. 2. A permanent valve is installed on the fitting.

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4. The valve is closed, and the tapping machine is removed. A branch connection is added, and the valve is opened. The new connection is ready to put into service. This field-proven TDW Procedure is quick and precise. Plugging / Completion Plug Systems 10 4

Hot tapping 1.

The four fittings are permanently secured to the line.

2.

Temporary SANDWICH® Valves are installed on the fittings, and taps are made through the valves.

3.

Two STOPPLE® Plugging Machines are installed. Product is diverted through the temporary bypass. The isolated section is purged. Modifi cations are made to the isolated pipe section. The new section is purged and equalized, and the plugging heads are retracted.

4.

The temporary bypass is removed. LOCK -O-RING® Plugs are installed in the STOPPLE® Fittings with a tapping machine. All equipment is then removed and blind flanges are installed on the fittings to complete the job.

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Tapping Machine

Tapping Operation

PIPE SECTION REPLACEMENT •

Severe damage may need to be cut out the pipe and replaced by ‘pre -tested’ sections.

•

This will require: •

Isolation of flow and pressure, depressurisation and purging of section to be replaced.

•

Hot-tap, Stopple and Bypass to bypass flow if the pipeline must continue to be in operation, perhaps at a reduced pressure.

Remove

Replace

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Cut out •

If line can be shut down, depressurized, depressurized, and evacuated, evacuated, a relatively relatively simple repair

•

If the line cannot be shut down, depressurized, and evacuated, a much more complicated repair:

 – Requires stopple stopple fittings (a way to stop the flow in the pipe) on both sides of the section to be replaced

 – After stopples are activated, section with defect is depressed, removed, and replaced

•

Bypass piping can be connected to stopple and used to maintain flow.

•

Stoppling and by-passing is really expensive

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We can bypass damaged pipe, and maintain flow by constructing a ‘hot tap, stopple, and bypass’. HOT TAP: TAP: cutting into a live pipeline using a special tee, welded or clamped to the pip STOPPLE*: insertion of a temporary plug into the line, through a hot-tap tee, to isolat BYPASS: attachment attachment of bypass pipe to a pair of hot-tap tees to provide a flow bypass aroundthe isolated section. TDW now have a One piece bypass fitting

Freeze plugging Freeze plugging is used to isolate ▪ Freeze

▪ ▪ ▪ ▪ ▪

a pipe segment containing a liquid without draining down entire line LN2 is circulated within a jacket around the pipe Temperatures are monitored to assure freezing of liquid Plug is locked in place by thermal contraction of the pipe Pipe to be frozen frozen should be subjected to NDE If plugged section is on test, plug should be clear of personnel

In-Service Welding Production welding procedures are inappropriate for welding on a line in service if the line contains a flowing gas or a flowing or quiescent liquid. Such conditions cause high weld cooling rates, which, when combined with susceptible base metal chemistry and the presence of hydrogen in the welding environment, may lead to underbead or hydrogen-induced cracking (HIC) in the heat-affected zone.

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In-Service Welding Weld cracking is avoided by one or more of the following: ▪ minimizing hydrogen in the welding atmosphere by use of low-H electrodes (E7018) or process (FCAW or GMAW) ▪ welding procedures that provide sufficient heat input for the pipe material chemistry and effective cooling rate ▪ temper-bead sequence welding procedures

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In-Service Welding

• Maintenance welding procedures are •

developed by weld procedure testing, computer thermal analysis, or measurement of heat-sink capacity and cooling rates. Maintenance welding procedures and welders are qualified in accordance with Appendix B in the 19th Edition of API 1104 (supercedes API RP-1107).

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WELD METAL DEPOSITION* We can grind smooth part wall defects in a pipe wall, and fill the area with weld metal.

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WELD METAL DEPOSITION* It is a simple and direct application of additional wall thickness, but always use an approved procedure that is applicable to your line/product/defect.We also need to reduce pressure prior to this type of repair.

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WELD METAL DEPOSITION: Advantages •

Gas Research Institute (USA) say weld deposition is feasible to 900 psi for minimum 0.125” wall thickness pipe. API 1160 limits this to >0.181” (4.5mm).

•

Can be useful where sleeves are not possible - at fittings and bends - or where access is difficult.

•

Fatigue and fracture tests at Edison Welding Institute (USA) have shown good properties.

•

Recognised in ASME B31.8.

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WELD METAL DEPOSITION: Concerns •

Defect assessment can usually show it is not needed.

•

Possible blow-out or penetration of pipe:  –

penetration depends on wall thickness, weld heat input and removal of heat by flow of fluid inside pipe.

•

The pipe’s static and fatigue strength must be restored, and significant defects must not be introduced (including hydrogen cracking in the heat affected zone).

•

The repair can be difficult to QA, and can show as small pits in an MFL pig run, due to material change, and may lead to excavation.

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In-Service Welding Recommended maintenance procedure qualification test arrangement Pipe coupon inclined at 45 degrees with fresh water flow. Simulated repair sleeve clamped in place prior to welding.

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In-Service Welding ▪ Welding on a line containing quiescent gas may not

▪ ▪

require a special welding procedure. However, if there is flow or if the sections are thick (e.g., a large hot-tap), use of low-H is strongly encouraged, particularly if CE is high. Preheat is unlikely to be effective where cooling rates are controlled by product in the line. If line is under pressure and t < 0.25 inch, use of low-H electrodes and limits on heat input to avoid burn-through are strongly encouraged.

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In-Service Welding ▪ Assurance that cracking has been avoided is

strengthened by NDE using UT and/or MPT of the weld, allowing 48 to 72 hours for delayed cracking effects. ▪ Alternatively, set aside procedure test coupon for 48 hours and check for cracking before destructive tests to establish a crackproof welding procedure – no delay in field needed. Al

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Weld metal deposition repair ▪ Codes allow repair of corroded areas by filling them with weld metal. ▪ Refer to “Guidelines for Weld Deposition Repair on Pipelines” by Bill Bruce, EWI, February 24, 1998, A.G.A. Cat. No. L51782 for further information. ▪ Useful for small areas that cannot be sleeved, such as bends, elbows, tees. Al

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Weld metal deposition repair Direct deposition repair welding procedure qualification test arrangement

Direct deposition weld repair cross section Al

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Pop Quiz True or false? • A reinforcement sleeve is ineffective for internal corrosion_____ • Composite wrap repair is not permanent_____ • Composite wrap repairs cannot be detected by ILI____ • Steel sleeves must match the pipe grade_____ • In-service welds should be made using low-hydrogen welding____ • The reason for using low-H welding is to avoid cracking____ • Steel sleeves should be tapered to the pipe thickness at their edges____

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CODES, STANDARDS & REGULATIONS

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Applicable documents Gas Pipelines ▪ 49 CFR 192 ▪ ASME B31.8 ▪ ASME B31.8-S ▪ CSA Z662 ▪ PRCI Pipeline Repair Manual ▪ Company SOPs

Liquid Pipelines ▪ 49 CFR 195 ▪ ASME B31.4 ▪ API 1160 ▪ CSA Z662 ▪ PRCI Pipeline Repair Manual ▪ Company SOPs

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Repair of Corrosion Repair Method

ASME B31.4

Cut out

ASME B31.8

Yes, as complete cylinder

Grind out Reinforcement sleeve (Type A)

No  Yes, if not leaking and not selective on ERW seam

 Yes, if not leaking

Pressure-containing sleeve (Type B) Compression sleeve

Composite wrap

 Yes Included as A or B

See as A or B

 Yes, if not leaking and d/t