1. ACCIDENTS DURING LPG PIPELINE PIGGING OPERATIONSBy
K.SRINIVASA RAO
Controller of Explosives
PESO, NAGPUR ,

2. PIGGING…?
The Pipeline Inspection Gauges or ‘PIGs’ used to perform various operations in the pipeline maintenance without interrupting the flow of the product in the pipeline.
The pressure of the product is the motive force on the pig to travel along the pipeline from pig launching station to pig receiving station by scrapping the sides of the pipeline and pushing the debris ahead.

3. OBJECTIVE To mitigate PIG accidents: * Identify Design flaws
* Review of SOPs & Risk analysis
* Review of HAZOP studies
* Modifications in P&I
* Installation of safety interlock systems
* The crucial role of pipeline operator in the pigging operations shall be reviewed and the contactor workers technical knowledge must be verified before pigging operations.

4. ACCIDENT IN BRIEF
The technical team of the oil company (pipeline operator) and the contractor personnel were undertaking the works to receive the pig at Intermediate Pigging station.
The crew isolated the receiver barrel from main line, de- pressurized the receiver barrel, opened the barrel door, and cleaning the debris inside the receiver barrel as they were doing this, Suddenly the pig got ejected under pressure through the barrel resulting in death of two persons, and injuring three persons.

6. ACCIDENT IN BRIEF
The pressure of ejection was so high that the dead and injured persons who were in front of pig receiving barrel door were thrown to the compound wall located at 9 meters, leading to death and injury.
The compound wall (on the opposite side of receiver barrel) also got damaged. The pig receiving barrel and its instruments (Pressure gauges, Safety Relief Valve, etc.) were found intact.
No indication of Fire/Explosion was noted.

7. CHRONOLOGY
The cleaning pig train (consists of cup pig, brush pig and magnetic pig ) was Launched from G.Konduru, Vijayawada .
The pig reached to IP-2, Suryapet after 3 days, travelling about 113 KM .
The pipeline operator SCADA control room remotely closed the Motor Operated Valve(MOV 1602) stationed at IP-2 on fateful day at hrs, and the pig was allowed to move towards the pig receiving barrel.
Attending personals opened the isolation valve after the balancing pressure on both sides of isolation valve.
After confirmation from contractor, the pig was received in the barrel at about 4:45AM.

8. CHRONOLOGY
On fateful day at about 11:00 Hrs, pipeline operator personnel and contractor personnel went through the procedure to receive the pig in receiver barrel, isolated the barrel by closing Isolation Valve and Kick-off Line Valves, released pressure in the barrel, and opened the barrel door.
The barrel was filled with debris/dirt up to 80-90% of its volume i.e. approximately Kg of debris was present inside the barrel.
Later the crew first collected 6 samples of muck in sterilized containers and then started clearing the debris with water by using a 1” water hose pipe connection, as stated by eye witness.

9. INVESTIGATIONS
The pipeline operator has not carried out Pipeline pigging operations in this section from past 10 years (since pipeline commissioning in 2004) .
it is very likely that large quantity of debris/muck at 80-90% of the volume of the receiver barrel and approximately Kg of it was recovered in the receiver barrel, might have restricted the pig movement at the transition point.

10. INVESTIGATIONS
The muck analysis reports of previous 10 pig runs have Fe2O3 at 80-90%, which clearly indicates significant corrosion and erosion rates in the pipeline.
Unfortunately, pipeline operator had launched a Coupled Bi-Directional Pencil-Brush pig which has a magnetic pig. The magnetic pig might likely have dislodged a large quantity of Fe2O3 and this might have restricted the other two pig’s movement in the 10” pipeline. The lower pressure in the receiver barrel increased the potential for the pig to blocked at the transition zone.

11. INVESTIGATIONS
There was a lack of technical analysis with respect to selection of cleaning pig, pigging parameters such as product, operational function, constraints, pig train length and clearance between the pig and the trap inside diameter etc .
There was no pressure indication in the 10” section immediately downstream of the receiver isolation valve, and this prevented the operators from identifying that any over pressures. Further, the absence of safety relief valve could not provide the backup protection for a pressure build-up.
The Standard Operating Procedure (SOP) for pigging operations did not adequately identify the potential for pigs to get blocked at transition zone

12. Pig Receiving and Launching Station( IP-2 ) Battery limits
Pig Receiver for LPG main Pipeline ( Dia 10”) coming from G.Konduru to Suryapet IP-2 Station)
Main Isolation Valve between Pig Receiving barrel & main Pipeline.
Pig Launcher for LPG main pipeline Line (Dia 10”) from Suryapet IP-2 station to Cherlapalli Secunderabad
PIG ALONG WITH LPG FLOW DIERCTION
First Pig signal receiver
Pig Receiving and Launching Station( IP-2 ) Battery limits

13. Figure Shows From Left to Right
Isolation Valve between Pig Receiving barrel & main Pipeline found in closed condition during visit. .
(d)
(c)
(b)
The floor was found spread with black sludge, debris near the pig receiving barrel.
(a)
Figure Shows From Left to Right
Upstream of main isolation Valve( LPG line coming from G Konduru)
Downstream of isolation Valve (towards pig receiving barrel
Damaged compound wall due to hit by the Pig.
Pig Launching facility (LPG line from Suryapet IP2 to Cherlapalli)

14. First Pig signal receiver
LPG Main Pipe Line ( Dia 10”) coming from G.Konduru to Suryapet IP-2 Station)
Pig Direction towards pig receiving barrel
Figure shows First Pig signal receiver position at upstream of Isolation valve

15. Differential Pressure Balancing Line
Main Isolation Valve between Pig Receiving barrel & main Pipeline.
LPG Main Pipe Line ( Dia 10”) coming from G.Konduru to Suryapet IP-2 Station)
Figure Shows the Isolation valve in between Main pipeline and Pig receiving barrel.

16. PIG RECEVING Section( Accident Site)
Safety Relief Valve
Pig Receiving Barrel
Vent Line
Receiver Door
Pig Receiving Barrel
(Dia. 16”)
PIG got STUCKED IN THIS TRASITION POINT
PIG BLEW OUT OF THE RECIVER BARREL IN THIS DIRECTION HIT THE PERSONS AND DAMAGED COMPOUND WALL
( 2 PESRSONS KILLED & 3 PERSONS INJURED)
PIG DIRECTION
Second Pig signal receiver
Pig Receiving Barrel
Drain Line
Kick-off Line
Pig receiver Pipeline (Dia. 10”) after Isolation Valve
The floor was found spread with black sludge & debris.
PIG RECEVING Section( Accident Site)

17. Figure Shows the Second pig signal receiver &Transition Zone
Receiver Pipeline Transition Zone
Second Pig signal Receiver
Pig Receiving Barrel starts from here
(Dia. 16”)
Pig Receiving Pipeline ends here
(Dia. 10”)
Figure Shows the Second pig signal receiver &Transition Zone
Note: The Pig might have stuck in the Transition zone (interface between end of Dia 10” of pipeline & start of 16” Dia of receiving barrel)as shown thereto on receiving barrel.

18. Figure Shows Instrumentation Details on Pig receiving barrel
Low Pressure Gauge (range 0-1 kg/cm2) on pig receiving barrel.
Low Pressure Gauge on Pig receiver barrel.
High Pressure Gauge (range kg/cm2) on pig receiving barrel .
Pig receiving barrel .
Figure Shows Instrumentation Details on Pig receiving barrel

19. Compound wall approx Thk 30cm.
Cleaning Pig ejected from receiving barrel and hit the compound wall.
Black colour debris were spread over the floor.
Pig retrieval Rod with a Hook found at the site of accident.
Service water line with Hose pipe connection to clean the debris from receiving barrel
PIG BLEW OUT OF THE RECIVER BARREL HIT THE WORKMEN ( 2 PERSONS KILLED &
3 PERSONS INJURED) AND DAMAGED COMPOUND WALL

21. Cleaning Pig ejected from receiving barrel and hit the compound wall.
Service water line with Hose pipe connection to clean the debris from receiving barrel
Fig:9 PIG BLEW OUT OF THE PIG RECIVER BARREL and Hit the compound wall (about 9 meters from the receiving barrel )

22. Figure: 10 After hit by that Pig , the debris of wall spread over up to 10 meters surrounding outside the compound wall.

24. ANALYSIS
The design of the pig receiving section (Figure-1) had not provided for a pressure indication and safety relief valve in the 10” line (immediately downstream of the receiver isolation valve and upstream of the 16”receiver barrel).
This prevented the operators from identifying over pressure in the 10”line, and a missing safety relief valve could not provide a backup safety either. The low pressure and a large quantity of packed debris/dirt (at 80-90% of the volume of the 16” receiver barrel) i.e. approximately Kgs in the receiver barrel increased the potential for the pig to get blocked at the transition point (where the receiver diameter increased from 10” to16”).

25. ANALYSIS
The pressure build-up of LPG and dirt/debris might have exceeded the operating pressure (35-40 Kg/Cm2) in the 10” line upstream of the stuck pig due to soaring atmospheric temperatures (of about 400C).
A sudden release of trapped LPG due to differential pressure formed by removal of packed debris/dirt (by cleaning it with water/pulling of pig manually with pig retrieval metal hook rod) might have caused a pressure drop inside the barrel resulting in instantaneous boiling of LPG at millions of nuclei.
This resulted in a very high increase in volume, leading to a massive wave of over pressure that might have ejected the pig like a missile from the receiver barrel, which in turn hit the workmen in front of the receiver barrel’s mouth resulting in the death of two persons, and injuries to three.

26. CONCLUSION
Pipeline maintenance and pigging operations are highly risk oriented technical filed jobs which requires a dedicated technical qualified manpower with a proper training.
In the history of pig accident cases at about 80% are due to human mistakes, skipping of pig schedules, adopting shortcut methods to complete the pigging hurriedly.
The crucial role of pipeline operator in the pigging operations shall be reviewed and the contactor workers technical knowledge must be verified before pigging operations.

27. CONCLUSION
Job safety analysis shall be undertaken by pipeline operator.
HAZOP studies shall be conducted to identify mechanical and instrumental system reliability.
Standard Operating Procedures shall be strictly followed.
Qualified and experienced technical manpower shall be deployed during pigging operations by the contractor as well as pipeline operating companies.