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How to Risk Assess Flanges before Hot Bolting.

What is Hot Bolting?


Hot bolting is a method for changing out bolts on piping flanges whilst the process piping remains fully or partially pressurised. It is also known as single stud replacement, line bolting or bolt replacement.


Is Hot Bolting safe?


Hot bolting is safe if you identify and mitigate the risks to personnel, the environment and the asset. The risks include temperature, pressure, process medium, flange condition, work access, etc.


A bolted flange after hot bolting with BoltEx®
A bolted flange after hot bolting with BoltEx®

The Fundamentals of a Hot Bolting Risk Assessment.


Before undertaking any risk assessment on potential flanges for hot bolting, a data-gathering exercise needs to be conducted to ensure that the flange design specification, inspection history, anomaly reports, accessibility and current flange condition are fully understood.


This data can then be used to formulate a risk assessment approach appropriate to the risk profile of the plant and the asset-owning organisation.


Inspection report examples
Inspection report examples

Flange condition assessment.


The cornerstone of any hot bolting risk assessment is the current flange condition. If the flange was inspected 6 months ago, get eyes on it today, if possible, before deciding whether it is suitable for the fitment of a hot bolting clamp. Don’t just rely on recent inspection reports.


The assessment of the flange condition is semi-subjective, using exemplar images for comparison. Generally, three grades of flange condition are arrived upon, whereby the grade of extreme degradation prevents the use of a flange clamp and any hot bolting altogether.


The other two grades of flange condition permit using a flange clamp, perhaps with the clearance of surface corrosion to ensure solid contact with clamp surfaces.



Examples of corroded bolted flange connections
Examples of corroded bolted flange connections

Understanding Risk Factors.


Fully understanding the risk to the personnel carrying out hot bolting is the primary consideration in any risk assessment. The process conditions within the flange connection will nearly always present the major risk.


Various organisations approach this differently, but the following elements are generally factored into the risk outcome decision:

  • Hazardous or Non-Hazardous Process Medium

  • High or Low-Pressure Process Medium

  • High or Low-Temperature Process Medium

  • Working at height, overboard or in confined space (or in combination)



A person working on a bolted flange connection.

How to Establish a Hot Bolting Risk Assessment Process.


SRJ has significant experience defining hot bolting procedures for organisations globally, which always include a risk assessment element. We understand that every company is different and, with client guidance, tailor each procedure to the competence of those delivering hot bolting on the plant and the corporate risk approach.


Hot bolting risk assessment decision logic
Hot bolting risk assessment decision logic


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