Repairment Methods of Pipelines

Southern Gas Association Transmission Operating Conference

New Orleans, July 2001

Eric Quick – Clock Spring Company L.P. Patrick Porter – Clock Spring Company L.P.

Economics of Pipeline Repair There are several repair options available to pipeline operators 1. Each option has its place and selecting the most appropriate option requires careful thought. The first consideration is the effectiveness of the repair. Will the repair return the pipeline to a condition that will allow complete serviceability? The second consideration is safety. How safe is the repair from both an installation and long-term serviceability standpoint? The third consideration is the immediacy of the need. If a defect has been day-lighted, and is seen to require immediate action then the repair alternative must allow this fast response. This factor will take on higher importance as new rules and regulations take effect. The last consideration is cost. Is there a significant cost advantage to one repair over another? Repair Options Typically, pipeline defects have been repaired in the following fashion:

• Removal of the pipe as a cylinder. • Grinding the anomaly to reduce the effect of stress concentration. • Depositing weld filler metal to replace the missing wall thickness. • Reinforcing with a full-encirclement, non-pressure-containing sleeve (Type A). • Sealing the defect with a pressure containment sleeve or clamp (Type B). • Removal of defect via hot tapping. • Reinforcing with epoxy filled shell sleeve. • Reinforcing with fiberglass reinforced composite materials.

Removal of the pipe as a cylinder Clearly, this is a very good repair alternative but has obvious disadvantages. The pipeline must be removed from service with all of the economic factors associated with loss of throughput. Pipe replacement also carries the safety and environmental risks associated with any pipeline construction. It is time consuming, requires heavy equipment and skilled labor. It is by far the most costly alternative and in most cases, the least preferred option. When several joints of pipe are involved in the repair or when there is a systemic problem with material, pipe replacement may be the only option.

1 Clock Spring® is a registered trademark of NCF Industries Inc. All rights reserved. Manufactured under license from

NCF Industries. The Clock Spring symbol is a trademark of Clock Spring Company L.P.

Grinding Minor scratches or surface imperfections can represent stress concentrators. It has long been known that these minor imperfections can be ground, or buffed, out of the pipe without any loss of serviceability. This is a good repair alternative for minor imperfections. The repair area should, of course, be inspected by appropriate NDE techniques to ensure that the defect has been completely removed and that there are no lingering imperfections. If the buffed area leaves less wall thickness than is required by code or company standards then the area can be assessed as a metal loss defect and a repair alternative for that type of defect selected. Weld deposition Weld repairs have long been accepted. Most operators feel comfortable working with welded fittings or mechanical sleeves for repair of pipeline defects. Welding onto in service pipelines has risks to the pipeline operator. These risks are: • Pipe-wall burn through/blowout • Hydrogen cracking • Metal decomposition • Previous welder-induced defects These risk factors need to be evaluated prior to choosing any weld-repair method.

Techniques for depositing weld metal have been proven for cases in which a defect is located on a sharp bend inappropriate for a sleeve. Weld deposition repairs are feasible to 900 psi for minimum 0.125-inch wall thickness pipe. Small diameter low hydrogen electrodes should be used with limited heat input. The restoration of static strength is accomplished with full-thickness weld deposition. Sleeves-Type A and Type B Pre-stressed welded reinforcement sleeves reduce bulging and hoop stress at the defect. Two general categories exist for reinforcement sleeves. Type A for non-welded sleeve ends and Type B for welded sleeve ends. The major differences between the two types are that Type B sleeves can be used to repair leaking defects, reinforce internal corrosion defects, and are utilized more frequently on larger defect areas. Training in proper welding techniques is extensive for proper installation of these sleeves and the risks of welding on the pipe mentioned earlier apply. Mechanical sleeves require less operator expertise when installing, however are generally more expensive.

Hot Tapping Hot tapping is a method of re-routing the pipeline product to allow a section of pipe to be removed without loosing full throughput. It is very expensive and is only used in extreme cases where no other alternative exists and the pipeline cannot be shut down.



Hot tapping can also be used to remove isolated defects from the pipeline. The equipment allows a small section, coupon, of pipe to be removed while the line is under pressure. The section of pipe removed is then re-established with a suitable weld on fitting. All of the risks associated with welding on the pipe, as well as the risk of penetrating a pressurized pipeline are present in this repair alternative. Epoxy filled sleeves This reinforcement sleeve is slightly larger than the pipe to be repaired. It is placed on the pipe to be repaired with a uniform annulus around the circumference. The ends of the sleeve are sealed and the annulus filled with a load transferring epoxy. This type of sleeve can be an effective repair for longer defects.

Clock Spring® Composite sleeve Clock Spring® is a composite sleeve that can be used to reinforce damaged pipe. Clock Spring® offers the following advantages; • Composite reinforcements avoid introducing welding associated risk. • Eliminates cost and service outages associated with conventional repairs, which

require pipeline shutdown prior to welding. • Clock Spring® restores the original pressure capabilities of the pipe and provides

resistance to further structural deterioration. • Repairs can be made without line-pressure reduction. • Clock Spring® can be installed easily without highly skilled labor or special

equipment. • Typical installation time less than 25 minutes. Training is required to ensure proper installation and performance. The figure below illustrates the simple design of the Clock Spring® reinforcement sleeve.

Figure 1. Clock Spring® Reinforcement Sleeve 2

Clock Spring® is a three-part system. • A patented unidirectional composite structure of glass fibers and a polymer base • A patented two part adhesive system • A proprietary high compressive strength load transferring compound

Once installed, the three elements bond together to form an extraordinarily strong, durable repair.



Selecting a Repair Alternative The effectiveness of the repair is independent of pipeline location and access. Table 1 summarizes repair options based on the defect to be repaired and the location of the defect in the pipeline. In most cases, this table will allow multiple repair alternatives.

Repair Method Weld Sleeve Sleeve Clock Clamp Hot

Defect Grinding Deposition Type A Type B Spring® Bolt-on Tapping Pipe Location Onshore Yes Yes Yes Yes Yes Yes Yes Offshore Yes No Conditional No Yes Yes Conditional Defect Location Straight Pipe Yes Yes Yes Yes Yes Yes Yes Gradual Bend Yes Yes Special Special Yes Yes Yes Sharp Bend Yes Yes Special Special Special No Yes Internal Defect No No Conditional Yes Conditional Yes No External Defect Yes Yes Yes Yes Yes Yes Yes Defect Type Corrosion No Yes Yes Yes Yes Yes Yes Leak No No No Yes No Yes Yes Dent No No Conditional Yes Conditional Yes No Gouge No No Conditional Yes Conditional Yes No Crack<0.4t Yes Yes Yes Yes Yes Yes Yes Crack>0.4t No No No Yes Conditional Yes Yes SCC Yes Yes Yes Yes Yes Yes Yes Wrinkle Bend No No No Special No No No Hard Spot No No Yes Yes No Yes No Arc Burns Yes Yes Yes Yes Yes Yes Yes Girth Weld Yes Yes Yes Yes Special Yes Yes Blisters No No Yes Yes No Conditional No Defect Size Area-Large No No Yes Yes Yes Yes No Area-Small Yes Yes Yes Yes Yes Yes Yes Pits<0.8t Yes Yes Yes Yes Yes Yes Yes Pits>0.8t No No Conditional Yes No Yes Yes

Table 1. Repair Application Summary 3



Safety considerations Some repair alternatives are inherently safer than others. Individual companies will assess the value of this safety factor differently. Pipe replacement carries all the risks of mainline construction. Full encirclement welded steel sleeves and weld deposition carry with them the dangers associated with welding on an operating pipeline. The risks include burn-through, cracking and the normal risk of hot work in the ditch. Type A steel sleeves have less risk associated with the welding but there is still the danger associated with hot work. Hot tapping carries the risks associated with cutting into a high-pressure pipeline. While hot tapping procedures have been tested and proven effective the risk still exists. Bolt on sleeves and composite sleeves are the safest repair alternative. Immediacy of the repair The immediacy of the repair need can be a significant factor in selecting the repair alternative. Hot tapping requires a careful planned program and is not effective for immediate response. Welded steel sleeves can be time consuming to fabricate and install. Bolt on clamps and composite sleeve offer an advantage to the welded sleeve for the immediate repair requirements that might be encountered. Weld deposition can also be fast and effective for some repairs. Cost of the repair Estimating the cost of the repair is difficult and controversial. The actual repair-cost equation is very straightforward; material cost + labor = repair cost 4. Material costs are easy to estimate. Labor, however, depends on individual company accounting practices and seems to invoke heated debate. The debate not only covers the value of the labor supplied but also the quantity of labor required for a given repair operation. There is no single set of correct assumptions so each operator will have to estimate repair costs based on individual considerations. Following is a typical assessment showing where cost will likely be incurred. Assume that the repair options selected for a particular defect are welded steel sleeve or composite sleeve. How does the cost compare? The most important factor is the physical length of the defect. This analysis will show that for short defects, composites repairs are more cost effective than steel sleeves but as the defect length grows to several feet, the welded steel sleeve may become an economical alternative. If safety is a concern, composites repairs will be the preferred option. Table 2., summarizes the labor and equipment rates used in the cost analysis. These rates will vary from company to company and will affect the outcome of the analysis.



Position Rate/hour Welder $35 Operator $34 Pipeliner $31 Apprentice $21 Equipment Welding rig $20 Backhoe $36 Boom truck $20

Table 2. Cost Rates (Fully burdened)

Assume that a single isolated patch of corrosion measuring 6 inches in diameter with a depth of 50% wall in 24-inch pipe has been uncovered. It must be repaired. The cost of repairing with both a welded steel sleeve and a composite repair are detailed in Table 2. In this case, the composite sleeve saves $900 over the steel sleeve at each installation. Now assume that the defect is 8 feet long. The welded steel sleeve is less expensive by almost $900 as shown in Table 3. At some point between 1 foot and 8 feet is a crossover point where the composite sleeve loses its cost advantage over the steel sleeve. Figure 2 shows this crossover point based on this analysis. This crossover depends on the cost and quantity of labor used in the calculation. Material costs are easy to predict and do not influence the cost equation to same extent as labor.

Type B Steel Sleeve Composite Repair Item Hours Cost Hours Cost

Preparation Welder 4 $140 - Pipeliner 4 $124 - Materials $80 $534 Installation Welder 9 $315 0 0 Operator 9 $306 5 $170 Pipeliner 9 $279 5 $155 Apprentice 9 $189 5 $105 Equipment Backhoe 9 $324 5 $180 Welding rig 9 $180 0 Miscellaneous $95 $85 Nondestructive Testing 2 $100 Total Cost $2132 $1229

Table 2. Cost Comparison – Isolated Single Repair



Type B Steel Sleeve Composite Repair Item Hours Cost Hours Cost

Preparation Welder 7 $245 - Pipeliner 7 $217 - Materials $300 $4272 Installation Welder 16 $560 0 0 Operator 16 $544 9 $306 Pipeliner 32 $992 9 $279 Apprentice 16 $336 9 $189 Equipment Backhoe 16 $576 9 $324 Welding rig

Boom truck 16 16

$320 $320

0 0

Miscellaneous $150 $140 Mobilization $400 $250 Nondestructive Testing 4 $200 0 Total Cost $5160 $5760

Table 3. Cost Comparison – 8-Foot Defect

What is clear from any analysis is that for a typical isolated defect composite repairs are more cost effective than steel sleeves. This along with the safety factor is making the Clock Spring® repair the preferred repair alternative.

Cost ComparisonSleeve vs Clock Spring

$-

$1,000

$2,000

$3,000

$4,000

$5,000

$6,000

1 2 3 4 5 6 7 8

Defect Length (Feet)

Cos

t ($)

Clock SpringSleeve Type B

Figure 2. Cost of Repair vs. Defect Length



The composite repair is cost effective for isolated defects and for extended defects up to approximately 7 feet in length. At this length, the welded steel sleeve may become competitive. It is not possible to provide actual cost detail for each repair because of widely varying cost structures and cost recovery of operating companies. Based on your own labor costs it should be a straightforward exercise to determine the most appropriate and cost effective repair alterative. If safety is a critical factor, Clock Spring® composite will win every time.

Conclusions The operations and maintenance personnel of pipeline companies need to have the knowledge to properly determine if a defect discovered in a steel pipeline should be repaired or a section of the pipe replaced. In the case of a repair, the available technologies, application techniques and materials need to be known. Selecting the appropriate repair technique is an important decision that requires an understanding of the risks and rewards associated with each alternative. Safety, permanency and effectiveness are the primary drivers of this decision but cost can become an important issue. Composites, like Clock Spring®, compete with older, more widely accepted weld repair techniques. These new repair options offer advantages over the more traditional repairs and are both more cost effective and safe. Each repair must be evaluated to determine the technically correct repair option and the most cost effective method of carrying out the selected repair. Composite repairs may not be the right repair option every time but they are an important alternative that can be very effective in most repair cases. References

1. D. Boreman, B. Wimmer, K. Leewis, "GRI Topical Report Repair Technologies for Gas Transmission Pipelines".

2. Clock Spring® literature. 3. Kiefner, W. Bruce, D. Stephens, "Development of a Pipeline Repair Manual",

PRCI Ninth Symposium on Pipeline Research, American Gas Association 1996. 4. Oil and Gas Journal October 9, 1995.



Documents

Repairment Methods of Pipelines