Chevron Floating Roof Support Providing Safe Working Conditions Under Floating Roofs

Types of Roof Collapse Roof Spiral Vertical Collapse this will result in the entire roof coming down the strength and condition of the legs have no effect on this type of collapse this is the most dangerous collapse mode Vertical Collapse will not result in complete roof collapse unless this initiates spiral mode above typically will result in excessive distortion in a local area not complete collapse to the tank bottom

Sources Of Complete Roof Collapse Roof Spiral Roof anti-rotation device may not exist or may fail. Lateral support provided by a modern rim seal is adequate to resist lateral movement. If the seal is removed without adding temporary lateral restraint, the roof can move laterally. The lateral movement alone is not usually enough to cause problems beyond local leg failures. However, it may initial rotational movement which is almost always the source of complete roof collapse.

Sources of Local Leg Failures Vertical Collapse The flexibility of most floating roofs allow them to withstand local leg failures without total collapse of the roof. Landing floating roofs which are holding water or product on the deck is the most common source of leg failure. A properly landed roof with corroded or damaged legs is also susceptible to collapse.

Prevention of Roof Spiraling Prevent Rotational Movement The Euler buckling mode of a floating roof leg determines its strength. Without restraint to movement at the deck, the allowable load of the leg is greatly decreased regardless of its condition or size. The forces required to prevent rotation are not excessive. Once the roof begins to rotate the loading on back up systems are much harder to quantify and design for. Properly engineered systems can insure the spiral mode is avoided. Prevent Lateral Movement Lateral movement can be easily controlled by blocking the rim. This limits potential movement of the roof to maintain stability.

Prevention of Vertical Roof Collapse Be sure roof is not landed with water or product on the deck. Open the deck emergency drain to insure the landed roof does not accumulate water. Inspect corrosion of legs and leg sleeves. Inspect plumness and alignment of legs.

Industry Standard Roof Support Insure rotational and lateral roof support. Unloaded roofs will not completely collapse when properly restrained against rotation or lateral movement. The restraint must be in good working order. If this cannot be verified, backup anti-rotation shall be used. Rim seals which are removed shall be replaced by rim blocks or other lateral restraints. Inspect the condition of each leg. Test leg thickness. UT or use a hammer test. Verify plumbness and proper landing of legs. Insure legs are not under designed. Prevent loads from developing on the roof deck. Provide temporary support to questionable legs.

Summary Floating roof supports are designed very similar to fixed roof columns. Fixed roof collapse is virtually non-existent because the fixed roof’s attachment to the shell limits any movement at the top of the columns. If floating roofs are similarly restrained against this movement they will be highly reliable. Local buckling or collapse of legs can be sustained by most floating roofs if anti-rotations and lateral support is present. Legs which are susceptible to local collapse can easily be identified for corrective action. Landed roofs should never be holding water or product on the deck. Back up systems should directly address the sources of collapse. Systems which are designed to support the roof after a failure mode is initiated are difficult to design as the loading during this failure cannot be easily predicted.