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CASE STUDY

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FAILURE OF MAST BULL LINE PULLEY IN RIG S-5

BRIEF DESCRIPTION OF INCIDENT:

Location: NLK

Rig: S#5 E-1400

Type of mast: SKYTOP

On 17/04/2017 while arranging for Rig

down Mast, during initial preparation/testing

for mast down job a sound was heard at

Derrick floor. After investigation it was

found mast vertical pulley towards driller

side got damaged (shaft dislodged from

mast member) and same ODS pulley got

slightly bent.

DS

ODS:

Bent

Pulley

How it happened…

Mast Bull line To equalizer pulley

& connect with other side bull line

Mast Bull line

Horizontal pulley

Vertical pulley

(damaged)Mast

Rig Floor

Mast bull line to anchoring on

mast

Casing line to fast

end pulley

Draw-

works

“A” frame

“A” frame pulley

Casing line

Contd……..

Extent of Damage DS: Shaft dislodged from mast memberODS: pulley got slightly bent

6.91

m 6.91

m

Contd..

Dislodged

shaft

Possible reason(s)

Already existing crack in the weld joint between shaft & mast

member. It was not visible as rig was painted in its earlier

location.

1# After inspection it was decided to remove

shaft assembly and replace with a new one.

2# A work programme was developed in

consultation with OEM, BHEL- Hyderabad.

Repairing job on damaged pulley:

1) Inaccessibility

2) Elevation

& to overcome this,

1) A platform was

fabricated just

below the pulley

2) Transport crane

to hold the Safety

metal cage at

elevated position

at different angle.

But Constrains for carrying out job:

Working

platform

Metal

cage

Pulley was removed along with shaft & web plate.

Repairing job:

Contd…..NDT was carried out on shaft, mast members.Observed crack on the Driller’s side shaft.

Crack

Contd……Cut and removed damage portion of mast member & replaced the same

Contd…..

Fabricated new web plate. shaft along with web

plate align with mast member

This end

welded

here

Contd..

Introduced stiffener plate in consultation with OEM,M/S

BHEL

Contd…

And final welding was completed

Additional stiffener plate as per OEM, M/S BHEL

DURING CUTTING & WELDING JOB

…….safety precaution against spark, fire….

As Loc.NLK was a gas well

(5k X-mas tree, flowing at

1400psi). Proper safety

procedure followed during

cutting/welding job,

- Well kept shut-in.

-Regularly gas reading was

checked in working areas.

-Fire extinguishers are kept

ready at D/F

-Running water kept on for

cooling near by well head areas.

After final welding, Carried out NDT of all load bearing points of

the newly done welding job. NDT was found OK.

&

BHEL, Hyderabad expert thoroughly examining the entire job.

Mast was lowered on 02/05/17 & placed on OFT.

****Please note:

--So far, What ever job carried out on S#5 mast was only

for carrying out mast down operation.

-- To put S#5 mast in operation again a details repairing

job was already worked out with OEM,BHEL-

HYDERABAD.

--Job is already started at NIA (From 18/05/17).

As per BHEL engineer job will be completed by

22/05/17.

Lesson learned /Remedial measures:-

--Before carrying out RU operation, at least once in a

year to carry out NDT of all load bearing points prior

to mast up operation

(i) Bull line anchoring point on mast

(ii) mast pulley(s) connection points on mast

(iii) dead end anchoring point.

It was already implemented at S#4, Loc-HYQ &

S#3, Loc-HYV

(iv) thoroughly inspection of bull line before R/Up

operation (Visual inspection already in place).

Proper health check up of our rigs by third party

expert. (e.g. DNV-GL at present is carrying out the

similar job for ONGCL in Sibsagar)

THANK YOU