1. Indian oil corporation Ltd
A case study on repair of corrosion defects in bridge attachment river crossing section of in-service petroleum pipeline - challenges and learnings PSC th March 2018 BY
Lalit Kumar Thakur
Operations manager
Indian oil corporation Ltd
WRPL, Abu road

2. INTRODUCTION
8” dia., 115 Km Koyali – Ahmedabad petroleum product pipeline is in operation since 1966
Intelligent pigging was carried out as per schedule maintenance
159 anomalies were reported in entire pipeline
More than 30 anomalies were on the pipe section in bridge attachment crossing across Mahi river
All anomalies were external and maximum metal loss was up to 31%

3. LIST OF TOP TEN ANOMALIES Pipeline chainage in Meters
Sr. No.
Pipeline chainage in Meters
Type of defects
Internal/ external
% Metal Loss
ERF as per ASME B 31G 1
Corrosion cluster
EXT 31
1.0006 2
Corrosion 30
0.8953 3 25
0.9351 4 21
0.9005 5 22
0.9649 6
0.9428 7 23
0.941 8 9 19
0.8969 10 28
1.0001
Three defects at chainages M (PR-I), M (PR-II) and M (Urgent) were required to be attended urgently because due to these defects the operating pressure of pipeline was restricted.

4. PROBABLE CONSEQUENCES OF ANOMALIES
Leakage in the pipeline due to these anomalies would result in pollution of river water, which could have serious cosequences as this water was used for drinking by neighbouring people
There was continuous loss of throughput due to pressure derating of the pipeline
Hence it was very essential to attend these anomalies primarily from envirnmental hazard and also from point of view of revenue loss

5. CHALENGES AND DIFFICULTIES AT SITE
In the Mahi River bridge attachment 550M of pipe is hanging below & at the centre of bridge
The span of bridge is 7 M and the height of the bridge from the water level is around 30 M
While planning for attending these defects the foremost challenge was to make an approach to the pipeline, without compromising safety of workers and inspection engineers attending the defects

6. CHALENGES AND DIFFICULTIES AT SITE
The Mahi bridge is the part of NH 8, traffic density on this highway is very high
The National Highway Authority, initially not giving permissions to work on this bridge considering
the highly dense traffic movement
old age of the bridge
After lot of persuasion, they agreed to give permission with the condition that
no traffic movement should be disrupted
detailed methodology & loading on bridge should be submitted to NHAI before start of work

7. APPROACH TO THE PIPELINE
After lot of deliberations it was decided to make primarily a scaffolding structure at bottom of bridge deck for full span
Detail design of the structure was carried out and found to be safe
This structure consists of inverted frames made of pipe of 1 1/2” dia having thickness of 3.4mm, spaced at 2.25 m C/C in longitudinal direction
These frames are longitudinally connected to each other by pipe(1 ½”dia, 3.4mm thk.). Lateral force due to wind would be resisted by plan bracing provided at intermediate location
The platform was a temporary structure made out of pipes hence connections between the pipes are achieved by using clamps. Steel perforated planks were kept over the steel frame which would act as working platform for maintenance work

8. APPROACH TO THE PIPELINE
SCAFFOLDING STRUCTURE

9. SELECTION OF SLEEVE FOR REPAIR
After erection of platform, whole length of pipeline was inspected, and it was observed that all the 30 defects on pipeline are basically on the bridge piers which were 15 in number
It was found that all the defects are due to external corrosion & pitting all along the periphery of the pipe surface in a pipe length of around 200 MM. And it was observed that at three locations the metal loss has reached up to 80% of wall thickness
Since the original wall thickness of pipeline was only 0.219” and metal loss was reached up to 80% at three locations hence welding of B-type sleeve was not recommended in view of possibilities of burn though while welding at these locations
Therefore three nos. of composite sleeves of clock springs were installed at these locations
Since the metal loss was not very much at other 12 locations, it was decided to repair them by welding of B-type sleeve

10. SELECTION OF SLEEVE FOR REPAIR
Composite sleeve is a three part system comprising of :
A high-strength, unidirectional composite structure of glass fibers and a polymer base;
A fast curing, high-performance, two-part adhesive system; and
A high compressive-strength, load-transferring filler compound.
The composite wrap works by sharing the hoop load carried by the pipe wall
This load is effectively transferred to the composite by the filler.
Composite sleeves can be used in non-leaking external defects upto 80% wall loss

11. CORROSION AT PIERS AND REPAIR

12. REASON FOR CORROSION
External corrosion & pitting occurred at the 15 locations on the pipe which were on the bridge piers
The clearance between the bottoms of the pipe surface to the top of the pier surface was hardly mm
Two bridge beams are resting on the piers and expansion gap between two beams is around 20 mm
During monsoon, water with soil fall on the pier top from these gaps
With time, this soil got collected over the pier top and the gap between bottoms of the pipe surface to the top of the pier surface got filled with soil and at some places the pipe was completely embedded in this soil
Because of this soil & water, the pipe metal enclosed into the neoprene sheet & clamp got highly corrosive atmosphere and got corroded slowly
Moreover, since the pipe is open to the atmosphere, CP protection is not provided. So the corrosion continued unabated

13. CORRECTIVE ACTION
In order to prevent the occurrence of same corrosion in future
Top of the piers cleaned at all 15 locations
Pipe painting was completed
3 ply-2 ply cold tape coating was carried out on the 2 M length of pipe, covering entire width of pier.
Once pipe approachability had been established after making such an elaborate platform with huge cost, following jobs were also carried out
servicing of all the hangers was carried out
Entire pipeline was painted with:
Two coats of Rust-O Cap, two component, high build, self priming, rust encapsulating, modified epoxy coating, 200 micron and
80 micron of high performance, acrylic aliphatic polyurethane coating
To give the pipeline a anticorrosion coating for long life.

14. CORRECTIVE ACTION

15. CONCLUSION
Maintainability of the pipeline is very important factor during design and construction phase of the project
Therefore sufficient thought should be given during project execution to ensure that pipe at bridge attachment crossings is approachable
either by deciding proper location of pipe or
by constructing a inspection platform along the bridge
Alternatively, crossing of rivers should be done by HDD method
For old pipelines where such factors have not been considered, the pipeline should not be neglected but
must be attended by construction of temporary platform or
by any other method so as to avoid corrosion leaks resulting in water pollution

16. Thank You