To:
Subject: BOP Flange Lifting Capacity

Question:

I need to lift a completely assembled 13-5/8� 5M BOP stack, can I lift it with some attachment to the top flange, and if so, how much weight can I lift by the top flange?

Answer:

Operators may lift BOP stacks by the top flange if they have some type of lifting attachment they can secure to that flange. Any safe lifting attachment shall display its rated capacity on a tag, or have that capacity stamped into its surface.

Flanges of different sizes and pressure ratings will have different load capacities, but any top flange on a BOP should suspend the same amount of weight as the internal working pressure would apply to the flange if the BOP contained its rated working pressure.

Working pressure will load the flange, in tension, an amount equal to the area of the flange bore multiplied by the working pressure. To determine this load, use the formula π r² x WP = flange load at rated working pressure.

For example, calculate the load capacity of a 13-5/8� 5M integral flange as follows:

Pi (π) = 3.1416

Bore diameter, 13-5/8� divided by 2 = radius (R) 6.81�

Working pressure (WP) = 5,000 psi

Formula: 3.1416 X (6.81 X 6.81) X 5,000 = 728,476 lbs

No 13-5/8� 5M BOP stack would ever weigh 728,476 lbs, so such a lift will probably never occur. A so called rated lifting capacity for an integral flange, using this method, would not have the safety factor usually used for lifting devices, but dividing the resulting number by two should satisfy even the most safety conscious. Keep in mind that any lifting device used to lift this maximum load would require attachment by a full set of flange bolts. Any lesser rated lifting attachment would require sufficient bolting to equal its capacity.

To re-state the formula including the safety measure of dividing the resulting total by 2:

π r² x WP ÷ 2 = conservative lifting capacity of integral BOP flanges.

If you know the weight of the stack you wish to lift, WOODCO USA can supply a lifting device with a rated and tested load capacity for that stack.

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