Geo12-FW-035

Second Pan American Geosynthetics Conference & Exhibition GeoAmericas 2012

Lima, Perú - May 2012

GEO12-FW-035 - INTERACTION OF TECHNICAL EXPERT AND LOSS

ADJUSTER DURING INVESTIGATION OF FAILURE OF HDPE LINER IN

COPPER SLURRY PIPELINE

Ian D. Peggs, I-CORP INTERNATIONAL, Inc., Ocean Ridge, FL, USA

Juan Pablo Duhalde, JUAN PABLO DUHALDE Liquidadores Internacionales, Santiago, Chile

ABSTRACT

A single 200 mm diameter 170 km long steel pipe lined with 5 mm thick HDPE was used to transfer copper concentrate slurry

from a mine to a sea terminal for onward shipping. A blockage in the pipe occurred. Staged forward and back pressure

increases would not dislodge the blockage. A by-pass to the blocked section was constructed for continued product

transmission and to facilitate removal and examination of blocked sections. Blockages consisted of deformed HDPE liner, an

unusual dislodged and overlapped section of HDPE, and fragments of a scale that the liner was intended to prevent.

The insurance loss adjuster retained by the mining company’s insurance company monitored the project and called in the

HDPE liner expert after the first inspection when it became clear that failure of the HDPE liner was a major factor in the failure.

There was scale and slurry in the liner/pipe interface. The major blockage was due to a large section of deformed HDPE that

had broken from the liner. An attempt had been made to make a pipe overlap weld in the liner. The weld failed and separated

allowing slurry between liner and pipe which in turn caused collapse of the liner and further blockages.

1. INTRODUCTION

The pipeline is a steel pipe approximately 200 mm in diameter intimately internally lined with an HDPE pipe approximately 5 mm

in thickness. The steel pipe is fillet welded with flanges approximately every 1.5 km. Lengths of HDPE pipe are butt fused

together, the outside diameter (OD) squeeze-out beads removed, and the pipe pulled with a wireline through an entry reduction

box, through the steel pipe, then released so that the liner expands to almost recover its original diameter and to be in intimate

contact with the steel pipe inside surface (ID). HDPE flanges matching the steel flanges are welded to the end of the liner. A

scraper removes the liner’s internal squeeze out beads, a sizing pig is passed through the pipe to ensure there are no major

flow restrictions, the liner is electrically holiday tested for holes, and finally given an air pressure test.

After a number of blockages in 2004 that could easily be removed by water jetting, on 4 May 2006 there was another blockage

in the pipe estimated to be close to the lowest part of the pipe, specifically between Flanges 143 and 143A (Figure 1). Several

attempts were made to move or break down the blockage by applying higher pressures from the plant and by applying back

pressures from downstream locations. The major blockage could not be removed, although it was thought to be moved about

500 to 700 m downstream then back upstream Between 4 May and 24 May 2006 an intense program of investigation, blockage

removal, pipe repair, and water flow/pressure testing was performed until the pipe was confirmed clear of all blockages.

2. THE LOSS ADJUSTER

With over 15 years of loss adjusting cases specially oriented to engineering and all-risks construction projects, we are involved

in major claims in the construction engineering area. Our experience, professionalism, accurate liability and loss management,

and also many years of technical experience and contacts in the worldwide reinsurer market ensure a fair assessment of loss.

In addition, we have a program of serious and constant technical improvement with the capability to form liaisons with experts in

complementary technical disciplines. This was how we became involved in the subject pipeline damage claim, in the northern

part of Chile.

We were appointed to evaluate the rupture in the high density polyethylene (HDPE) interior liner in the steel pipeline, that

showed serious and several damages in different parts of the pipe. We needed to determine the root cause of the failure to

understand if this was one damage event or several different damage events, related to, or independent of the initial failure

event.



Initially the assured focused on continuing to operate the plant in order to minimize its loss of business and the business

interruption claim that would need defending. They constructed several ponds to store concentrate while investigating the

pipeline, constructing a by-pass pipe around the suspected blockage locations, taking samples of the pipe/liner and contents for

immediate investigation and for future investigation to determine the initiating cause of the failure. At this stage the loss adjusting

team was called in and began to collect all relevant data and records (dates, times, blockage locations, pipe forward and back

pressure tests, slurry concentrations, photographs, construction records, etc) and anything else that might help identify the

cause of the problem.

After the loss adjuster gathered all the available information, requested additional supporting and continuity generating

information, and after looking at the multiple failure locations and samples therefrom it became apparent that this was not an

easy failure to investigate, primarily due to the fact that samples had already been taken by others, not knowing what really

might be needed. However, it was apparent that the primary failing element was the HDPE liner and that a polymer

performance expert was needed on the loss adjuster’s team.

3. LINER INVESTIGATION

Due to a previous thorough and successful joint investigation of an evaporation pond PVC liner failure, (Peggs and Duhalde,

2005) the loss adjuster retained Dr. Peggs to perform the investigation. The failure had occurred on 4 May 2006 and the

pipeline shut down within 8 minutes. The loss adjuster made his first site visit on 29 May 2006 when samples had been

removed and repairs were already underway. Dr. Peggs made his first site visit on 9 to 12 April 2007, almost 1 year later. A

second visit to confirm locations, orientations, and interrelationships of available samples and to seek additional samples from

the removed and stored pipes was made on 16 to 18 May 2007. Therefore, the failure had occurred and samples were

removed well before our technical investigation.

Several interesting features were found at locations shown in Figure 1.

Figure 1. Samples and their locations



A large amount of scale (Figure 2) had formed on and spalled off the HDPE liner, a feature that the liner was supposed to

prevent. The scale had gained access to the steel pipe ID and liner OD interface and the HDPE liner had collapsed in several

different geometries from a simple “celery stalk” cross section , through a more complex W-shaped section (Figure 3), to an

almost total circumferential collapse at Flange 144A (Figure 4A). At Flange 144 a collapse had been “blown out” probably

during one of the high pressure blockage removal cycles, as also shown in Figure 4B. The “A” flanges were found during the

investigation.

Figure 2. Scale on HDPE liner ID (left) and on steel pipe ID – both old and new scale (right)

Figure 3. Collapse geometries of HDPE liner



Figure 4A. Collapsed liner at Flange 144A

Figure 4B. Blown-out strip at Flange 144

On one side of the road in Figure 1 a sample we called The Claw (Figure 5) had been removed but by the time of our

investigation no matching break had been, or could be found. The abraded and rounded edges of this sample indicated that it

had been existent before the ultimate blockage occurred.



Figure 5 . The Claw sample

A sample called The Monster (Figure 6) was found between Flanges 143 and 143A in Figure 1. Upstream of this sample is

where the major blockage, about 4 m long, occurred (Figure 7). Close examination of this sample suggested that it had been

inverted during one of the forward high pressure cycles when the blockage was thought to have moved 500 to 700 m

downstream. The Monster had been the most upstream sample in the general area of blockage. Further forward pressures

were unsuccessful in again moving The Monster. However, it was reported to move back under a back pressure cycle.

Figure 6. The Monster sample as removed from pipe (left) and after storage (right)



Figure 7. Blockage upstream of The Monster

It had been proposed that the long downstream – pointing ears of The Monster were originally mated with The Claw, but with

several flanges and other samples between the two this was not possible.

By far the most interesting sample, was a seemingly overlapped section of piping on the opposite side of the road to The Claw

as shown in Figure 8. Every attempt was made to pull the 1 m long overlap apart but all were unsuccessful.

Eventually the section was cut longitudinally and found to be partially welded (Figure 9). It was as though the upstream part of

the pipe had been inserted into the downstream part of the pipe after the OD of the inner segment had been ground for welding

Fusion was intermittent mostly because, as would be expected, the inner segment of pipe had buckled through a “celery” cross

section to total collapse.



Figure 8. Marking upstream end of overlapped liner

Figure 9. Two halves of overlap weld. Outer segment (O), collapsed and abraded inner segment (I), weld boxed. Taper on

inner segment arrowed.

It was claimed by other parties that the welding had occurred as a consequence of interface friction after the HDPE liner broke in

service and the upstream segment was pushed into the downstream segment. However, this would not explain the tapering of

the inserted end, nor the grinding marks on the OD of the inner segment. There were no grinding marks on the ID of the outer

segment which would be more difficult to reach. And it would not be possible to make any type of friction weld in a “dirty” flowing

slurry environment.

On the other hand it would seem illogical for anyone to attempt such a weld, to successfully pull it into and along the steel pipe,

and to pass sizing pig inspections and pressure tests. However, the feature was present.

This was how we started putting this puzzle together, and how we approached our cause and sequence of events

determinations. It was necessary to prepare such a sequence of events that would complement the actions and observations

of, and be accepted by, the assured. This would enable us as loss adjusters to present a serious and technically defensible

presentation to the assured concerning activities and costs covered and those that would be refused. It was also necessary to

identify the as-constructed technical details that would not have been accepted by normal quality control and quality assurance

procedures and that contributed to the failure but that would not be covered..

4. CAUSE AND SEQUENCE OF EVENTS

There were many blockages in the pipeline between Flanges 143 and 158, but several could quite easily be removed by jetting

with water. These blockages would be caused by the scale build-ups initiated at geometrical anomalies in the liner ID or even

I O

I O



simply by a piece of tumbling scale digging into the liner and becoming immobilized. However, the main blockage was caused

at The Monster, but where did the large piece of liner come from and how was it formed?

Reports of the pressure cycling events indicate that there were basically two or three forward pressure events at pressures up to

21.4 MPa followed by three back pressure events up to 13.8 MPa. The operating pressure of the line is ~9.7 MPa. Initial QC

pressure testing was performed at 13.8 MPa. Therefore, the de-blocking pressures are the highest pressures experienced by

the liner, and could significantly affect/modify its in-situ geometry. However, its surface condition, such as abrasion, would not

have been affected since the line was shut down in only 8 minutes.

The major blockage was first projected to be at the lowest part of the line, between Flanges 143 and 143A, but probably closer

to Flange 143A. During the first forward pressure event, at 17.9 MPa, it was reported that this blockage moved about 500 to

700 m downstream before it came to a stop and could not be moved again, even at a forward pressure of 21.4 MPa. A

movement of 500 to 700 m would place it at least 100 m downstream of Flange 144.

During the first back pressure event, at 22.1 MPa, there was no movement of the blockage. However, during the second back

pressure event, at 17.7 MPa, the blockage was reported to have moved back more or less to its original position where it

remained stationary. Subsequent back pressures up to 20.3 MPa could not move it further. This location was where it was

found, upstream from Flange 143A. Therefore, it reportedly moved past Flanges 143A and 144 in both directions. However, it

could not have moved past Flange 144 without destroying the collapsed liner at the downstream part of Flange 144. This, of

course, assumes that the liner collapse at Flange 144 was existent before The Monster moved downstream, and was not

caused by one of the subsequent back-pressure events. This is a reasonable assumption because of the amount of hard

deposit found behind the similar collapses at Flange 144A.

Therefore, The Monster did not in any way originate from as far downstream as The Claw, so was not associated with The Claw.

It is difficult to imagine The Monster traveling very far at all, certainly not past the additional ID geometrical “steps” (butt weld and

faces) associated with a flange. When it formed, there would be much deformation of the liner downstream of the piece that

broke away. It is doubtful whether The Monster could completely pass through any badly deformed, reduced cross section liner

in its path. However, it is a little more possible that it could travel backwards when back pressured. But, even then, it would be

unlikely to travel much further than the upstream fracture face from which it originated. Therefore, it is most likely that it

originated close to where it was found. Examination of several photos (e.g. Figure 11) of The Monster prior to its removal from

the pipe shows the liner to be intact. Therefore, there is no question that it has moved from its original position.

Figure 11. The Monster when pipe was cut, Note intact liner



That the last direction of movement of The Monster was upstream is demonstrated by the two ears pointing downstream. They

could only have been reversed from their original upstream-pointing position to their final downstream-pointing position during

the forward pressure to back pressure transition. The following explains how this could happen, as illustrated in Figure 12.

Figure 12. Schematic of possible Monster formation

1. A blockage of the pipe occurs due to scale build up nucleated, most likely, at a geometrical step in, or a partial collapse

of, the liner ID. As the most upstream blockage this has gathered the scale from the longest run of pipe and from acid

cleaning (scale spalling) after a 2004 blockage.

2. The pressure behind the blockage induces a shear stress on the ID of the liner which eventually exceeds the shear

stress between smooth liner OD and smooth steel pipe ID. If at any location there is liquid between pipe and liner and

therefore a similar pressure behind the liner as inside the liner, liner movement will occur earlier. We know there was

slurry in the liner/pipe interface.

3. The liner will start to slide along the pipe, generating tensile stresses (and ultimately a tensile break) at the trailing edge

of the moving section, and a compressive stress at the leading edge. When a break occurs, allowing liquid behind the

liner, movement will be accelerated.

4. The compressive wrinkles built up in the liner at the leading edge of the moving section will ultimately fold and collapse

into the center of the pipe as the upstream moving segment tries to penetrate the static downstream segment, similar

to the overlap weld.



5. As this penetration occurs the moving liner will tend to an S-shape along its length. However, inward collapse,

lengthening of the S, and penetration of the upstream moving part into the downstream static part will be hindered by

the stiffening effect of the wrinkles and the compressed scales and particulate matter causing the blockage. Movement

will become severely restricted.

6. At some point a tensile break will occur at some position in the middle section of the “S” - between the leading fold and

the trailing fold.

7. When the back pressure is then applied the blockage will extricate itself from the downstream static section, and

fractured ends, prevented by the damaged downstream liner from being pushed out will instead be unfolded and pulled

out.

8. The ears will occur where the circumferential break was at the trailing fold of the “S” shape, and no ears will occur

where break was at the leading (downstream) fold.

9. The axial tears would occur preferentially along the thinner already-stressed folds of the celery-shape collapsed liner,

essentially as shown in Figure 4 of The Claw.

10. The blockage would then move upstream until the 4 m long plug of shattered scale, or parts of The Monster, met

another obstruction, most likely the upstream or downstream edges of the hole in the liner from which The Monster

originated.

All other things being equal, this scenario suggests a downstream movement about the length of the ears (<1m), and an

upstream movement of at least the length of the ears. Therefore, it would be expected that The Monster has, in fact, not moved

very far. It is most unfortunate, and a major omission in the original investigation, that the missing liner from which The Monster

originated was not located.

It should be noted that the as-found geometry of The Monster could be quite different to what it was when the blockage

occurred. In fact, the compressed wrinkled geometry could be a function primarily of the high pressure events, the initial

blockage simply being a function of a locally collapsed liner that could result from a flaw in the liner that allowed liquid behind the

liner as at the overlap weld. Had the origination of The Monster been found a much more complete analysis would have been

achieved.

The area around the overlap weld is an equally interesting area which indicates much more graphically the condition of parts of

the liner at the time of the blockage. As indicated above, the evidence is clear that the weld was made during the installation

process. Although it is difficult to envision the need for such a weld, why anyone would attempt it, and how such a weld could

be successfully made, it is even more difficult to imagine it being made by friction processes while the pipe is in service or being

tested.

5. SUMMARY

Therefore, while a number of individual failed liner sample geometries can be explained, it was not possible to identify the

specific initial cause of the blockage and the exact sequence of failure events, given the liner samples and pipe sections

available. Clearly, the loss adjuster and appropriate experts need to be involved during the initial investigation in order to obtain

all the relevant information and samples, rather than to be called in a year later. The initial involvement of the loss adjuster

enabled the assured to construct temporary ponds for the containment of manufactured product as repairs to the pipeline were

being made. This required some unexpected costs, but costs that the loss adjuster recommended be covered so as to avoid

much larger payments that could have resulted from a business interruption claim. The plant never did shut down.

Then, having determined the cause and nature of the failure, those items related to pre-existing damages that occurred during

construction of the pipeline, such as the overlap weld, were denied. Ultimately the assured received about 75% of the claim or

about $4M for physical damage. Had a business interruption claim been necessary, the potential payout for the insurance



company could have amounted to 5 or 8 times as much. Thus, the initial cooperation between loss adjuster and the assured

was of benefit to both parties.

REFERENCES

Peggs I.D. and Duhalde J.P., (2005), Investigation of PVC Liner Leakage in a Very Large Evaporation Pond, Geosynthetic

Research Institute Conference, GRI19, Geosynthetic Institute, Folsom, PA, USA.

Documents

Geo12-FW-035