What types of failure do anchor bolts experience?

Much of the working development length of the anchorage is hidden from view due to embedment into building construction materials, such as brick, stone, mortar, wood, and concrete. In industrial facilities, anchorage of process stream lines, vessels, and rotating/reciprocating equipment onto supporting foundations is handled by threaded metal rods embedded into conventionally reinforced concrete. Unfortunately, the condition of the ‘business end’ of the anchor bolt is unknown until an owner/operator experiences an unfortunate event in the form of:

• Bolt tensile failure
• Pullout (concrete tensile) failure
• Lateral bursting (blowout) failure
• Localized bearing failure
• Concrete splitting failure

 

Deteriorated anchor bolt conditions including metal corrosion, lateral movement, and Ioss of protective cementitious grout.

In petrochemical facilities, anchor bolts are used to fasten process vessels or machines to a foundation structure, thus allowing the loads to be transmitted to the foundation, and ultimately to the earth. As with concrete infrastructure, all too often anchor bolts are taken for granted and the thought of providing a maintenance budget for these critical fasteners is more often an afterthought, or a direct result of a failure. Anchor bolt failures, in some instances, can generate a process outage or a more serious accident involving personal injuries, such as when conditions precipitate a ‘failure without notice’.

Corrosion under insulation (CUI) is often the culprit in anchor bolt failures, allowing insidious corrosion processes to accelerate unnoticed when the anchor bolts are hidden from view by insulation materials. Recognizing telltale signs, such as rust staining though insulation systems, increases in vibratory movement, and misalignment of equipment; can provide owners/operators with the risk reduction opportunities when coupled with a thoughtful assessment strategy.