November 2019

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Inspection: Best practices for inspecting guyed structures

Guyed structures are common in petrochemicals, oil and gas and chemical industries. Half of the installed flare structures at many facilities are guyed. Various routine inspection programs are in place to examine these structures. This work describes some very basic checks, which should be in place to maintain their mechanical integrity.

Anwer, A., Contributing Editor

Guyed structures are common in petrochemicals, oil and gas and chemical industries. Half of the installed flare structures at many facilities are guyed. Various routine inspection programs are in place to examine these structures. This work describes some very basic checks, which should be in place to maintain their mechanical integrity.

Before proceeding to inspect guyed structures, major components need to be listed (FIG. 1). These include:

  • Guy wire
  • Guy attachment
  • Anchor
  • Structure.

Inspection programs must be developed based on these four components.

FIG. 1. Typical guyed structure.
FIG. 1. Typical guyed structure.

The most important component in a guyed structure is the guy wire. Since all the load is transmitted through this component, it is the primary lifeline of the structure. Other components—the anchor, guy attachment and the supported structure—are important, but their chances of failure are remote.

Guy wire

The basic and the foremost inspection of a guy wire is to perform a thorough visual check. This should provide information related to the general condition of the wire, especially the lubricated portion. Grease is an essential component to protect the guy wire from external conditions. A visual inspection will determine the condition of the grease. With the passage of time, grease solvent dries out and starts to crack. These cracks eventually provide access to external conditions, especially air moisture that can penetrate the guy wire and cause internal corrosion. An effective penetrative lubricating system should be made essential for guy wires to protect against the external atmosphere. That system should be applied at a set interval (e.g., every 2 yr).

Tensioning of the guy wire is essential to its load bearing capability and overall stability of the whole guyed structure. This should be ensured as per the recommendations provided by the manufacturer. This exercise is normally coupled with a verticality survey, as well where the readings are taken, and appropriate tensioning of wire is completed.

The third check on a guy wire is to perform an electromagnetic test—magnetic flux leakage (MFL) to ensure if there is any active internal corrosion. This is important regarding the condition of grease/lubrication over the guy wire. Typically, internal corrosion testing should be completed every 2 yr–3 yr. Guyed structures installed in moist, humid or marine environments should be inspected for internal corrosion on a regular basis.

Guy attachment

This attachment is a set of components at the structure/stack side of the guy wire. It typically includes a lug, which is normally welded to the structure. Along with the lug, there is an anchor shackle and connectors, such as eye bolts, thimbles or ferrules, which hold the wire in position. This set should be inspected visually for their external condition, which is essentially a check on their coating system. Any discovery on their galvanizing condition or other coating system should be addressed. A zinc epoxy coating system can be used for any touch-ups required or a full round of blasting and painting. A lug attachment weld should be considered for a general check-up using the dye penetrant testing method.

Anchor

A guy wire is connected to the guy anchor, which contains components such as turnbuckles, thimbles and wire rope clips. Wire rope clips should be checked for any looseness. Turnbuckle threads need to be inspected against environmental protection. External corrosion is the major damage mechanism that can affect the functionality of these components. Selection and application of an effective protective coating system should be ensured. A concrete ground anchor should also be examined for any abnormality. If required, a civil inspector may be requested to join for a combined interval inspection.

Structure

Mechanical integrity of the structure being supported through a guy wire is also important. A hollow structure, which is carrying the load of the main component being supported, should be inspected visually and with appropriate non-destructive testing of its weldments. Structures having verticality issues, along with gaps in guy wire tensioning, can develop defects over a period, which may go unnoticed. HP

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