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How the Hot Bolting Procedure (Single Stud Replacement) improves safety and turnaround efficiency

With a growing number of ageing assets across the world, corrosion is becoming a major issue, with costs to the world economy estimated at $2.5 trillion dollars per year. Corroded fasteners on bolted flanged joints are a major part of this, due to the integrity concerns degraded nuts and bolts raise.

An increasing focus on the integrity of bolted flange joint assemblies has resulted in operators being more proactive in the replacement of corroded and degraded fasteners as they tend to take up a large portion of time during turnaround and maintenance scopes, directly affecting the operating costs of any asset.

What is Hot Bolting, or Single Stud Replacement?

Single Stud Replacement (often referred to as ‘Hot Bolting’), is defined in both ASME PCC-1 and PCC-2 as: “the sequential removal and replacement of bolts on flanged joints while under reduced operating pressure.”

ASME PCC-2 ‘Repair of Pressure Equipment and Piping’ covers single stud replacement in the introduction of Article 3.11. This is globally recognised as the best practice on the subject.

Traditionally, bolt replacement activities have been included as part of planned maintenance shutdown activities. However, we see more and more that Operators and Asset owners are increasingly engaging in bolt replacement activities pre- shutdown whilst the process remains online (live). As maintenance shutdowns are time sensitive and pose significant risk to processing capabilities, Operators and Asset owners are looking to perform as much of this work during normal operating conditions, or using single stud replacement pre shutdown to ensure bolt removal efficiency in order keep costs within budget.

When should you use Single Stud Replacement?

There are several reasons why operators and asset owners look towards innovative solutions like Single Stud replacement. These include:

Replacing Corroded Fasteners
This is the most common reason, ensuring integrity of the bolted flange joint and protection of the environment.

Upgraded or alternative bolt specification
Hot Bolting (Single Stud Replacement) can also be employed to upgrade the material specification or grade of bolts. This may be required due to insufficient mechanical strength or incompatibility with joint component materials.

Non-destructive inspection routines
Inspection may also reveal fasteners that have metallurgical defects, such as stress corrosion cracking. The location of these defects may not be visible to the naked eye or can be obscured by the flange or the gasket.

What are the advantages of Single Stud Replacement?

The key advantage of Single Stud Replacement is it allows you to minimize the threat of integrity by performing work on a ‘live’ line.

Using this method eliminates the need of a plant shutdown - typically allowing the operation to be performed with no or limited disruption to production.

Not breaking containment during maintenance events limits the need for leak testing and return to service activities which enables more maintenance to be completed within scheduled downtime or a more accurate estimation of the timescales.

The time spent on disassembly of pipework activities prior to any shutdown or turnaround can be dramatically reduced – adopting the Single Stud Replacement methodology can increase efficiency during shutdowns by up to 30%.

Conclusion
In an environment where safety is paramount, it is imperative that the integrity of all bolted flange joints are monitored, regularly inspected and addressed when a threat is discovered to ensure that asset integrity is maintained.

Performing Single Stud replacement activities prior to maintenance turnarounds enables Operators and Asset Owners to predict bolt removal timelines more accurately for any work scope. This provides reassurance that these critical elements will not compromise the success of the operation - ultimately achieving a leak free start up.

It is vitally important to utilize experienced personnel from specialist service contractors when planning and executing these tasks. The most effective way to do this is to employ specialist contractors who have purpose-designed equipment, and a successful track record of prior engagements for removing corroded bolts.

Contact us for more information on Single Stud Replacement and Hot Bolting.