Overloading Leads to Catastrophic Failure of
Crane Boom AT AN OIL RIG PLATFORM
A lease operator was performing a well permanent abandonment
(PA) on an Outer Continental Shelf (OCS) platform. Operations were being conducted to pull the
3.5" workstring and casing knives from the well after using a power swivel
to cut the 9 5/8” and 10 3/4” casings. The
cutter assembly had become stuck while mechanically cutting the casings, and
the hydraulic cylinders on the swivel stand were used to free the stuck knives.
The cutter came free from the casing and the assembly was ready to be pulled
from the well using the crane.
The workstring and knives weigh approx. 6,600 pounds. The load line on the platform crane was
attached to the workstring using pipe elevators. The load chart in the crane indicated that the
crane could perform a static lift of 21,448 pounds and dynamic lift of 16,780
pounds at a boom angle of 63 degrees. The
boom was raised to a 63 degree angle and the crane operator then proceeded to
pull on the workstring until 21,000 pounds was displayed on the weight
indicator with no success. The crane
operator stated "looked like workstring was stuck.” After slacking off on the load, a second
attempt was made to pull the workstring and knives from the well. The crane operator stated that "the
weight indicator in the crane cab was displaying 21,000 pounds during the
second attempt.” The operator then
stated that "all of the weight fell off of the indicator at which time the
crane boom began to fall to the deck of the platform.”
The crane boom, as well as a power pack, came to rest on the
power swivel stand that had been used for the cutting operation. The tip section of the boom came to rest at
approximately 90 degrees to the right side of the main stem of the crane boom. No personnel were injured, and all were accounted
for immediately following the incident.
An investigation of the incident concluded that the following
factors contributed to the accident:
•
Incorrect load chart was used at the time of the
incident.
•
The crane operator used static load limits when
pulling cutter assembly from the well instead of using the dynamic load limits
as required by the contractor’s SOP.
•
The bore holes of the pin connections in the
boom showed excess wear thus causing slack in the connections and improper load
distribution in the boom.
•
The diagonal lacing, boom cords, and pin
connections of the middle boom sections were found to be corroded.
We recommend the following prior to use of cranes on OCS
platforms:
•
Conduct proper crane pre-use inspections as per
API RP 2D, C.4.1.2a which should include proper load chart verification.
•
Conduct proper crane maintenance inspections as
per API RP 2D, C.4.1.2 which should include thorough inspection of boom
connections and proper load chart verification.
•
Adherence to the SOPs and procedures put forth
by both the operator and contractor while conducting lifting operations.
•
Use the load chart for the dynamic load limits
when pulling tubulars from wells instead of using the static load limits.
•
The Crane Operator shall verify that the hook
load is within the crane’s applicable static or dynamic rated load at the
radius for which the load is to be lifted.
•
Crane boom pull shall never exceed the
calculated weight of the hook load, block, and rigging.
