Welded vs bolted joints – raising the standards

Joint integrity is the cornerstone of safe and leak-free operation in a pressurised system.

Correct assembly is one of the primary factors integral to the integrity of a bolted joint. Up until now bolting technicians have not been held to the same competence standards as welders.

However, their work objectives are directly comparable. For example, when comparing bolted and welded joints in the oil and gas industry, standards are very different.

Similar disparities exist in other major industries, including mining and energy, infrastructure and process engineering, where pressurised joints are involved.

When dealing with welded joints, engineers need to ensure that they have strong material control, documented and approved procedures and formally coded welders to perform the task.

In addition welds are tested using non-destructive techniques and verified through hydro and/or gas-testing methods. All of this is supported through fully documented traceability. These mandatory standards for welded joints have not typically been applied to bolted connections.

However, things are changing and 2013 proved to be a landmark year for those concerned with the management and assembly of bolted joints as two major standards were published highlighting the requirements for competent bolting. 

The American Society of Mechanical Engineers (ASME) updated the 2010 PCC-1 ‘Guidelines for Pressure Boundary Bolted Flange Joint Assembly’- this now includes an appendix defining the requirements for training and qualification of engineers working in the field of bolted joints.  

In addition to this, the European Committee for Standardisation (CEN) re-published EN1591 Part 4 with modifications. This is now referred to as ‘Flanges and their Joints – Part 4: Qualification of personnel competency in assembly of the bolted connections of critical service pressurised systems’.

Hydratight pioneered the concept of treating the bolted joint as though it were a weld and has practised the essentials of this standard for more than 20 years.

Hydratight have provided formally qualified and competent bolting craft personnel during this time, with all craft personnel undertaking classroom training, followed by practical workshops and examination before being permitted to work in the field on live projects. 

Through the publications of these standards, industry has been provided guidance in the assembly and assurance of bolted connection similar to the control and assurance of the welded joint.

Like the welded joint, field personnel will have to prove their competency every three years, document their activities using pre-approved procedures and traceable bolt loads and maintain a permanent record for future reference.

Providing these standards are rigorously followed, asset owners can expect significant payback; reduced leaks, improved safety performance, projects built or returned to service on schedule and within budget.

Joint integrity data management

Hydratight have championed the concept of treating bolted joints to be considered as critical as welded connections. As a result, they have developed training and competency programs to ensure that all bolting operations are carried out with an uncompromising approach to safety. 

Whilst these comprehensive training programs are mandatory for Hydratight’s craft personnel, they are also available to customers and to the general market.

Clearly defined procedures and acceptance quality standards supported by well-maintained data are crucial for assuring leak free joints.

As standards for joint closure and maintenance tracking have not previously existed, asset owners/operators have adopted different systems.

Some rely on the memory of the maintenance team; others keep paper-based data records and others use spreadsheet-based tracking registers. Typically all of these are prone to failure over time.

As assets age and their nature of use changes (e.g. contain different and/or more corrosive contents) risks increase. With the passing of time, personnel and rigidity of data storage and retrieval systems finding the correct information becomes more difficult. This potentially exposes major problems.

Well thought out and proven software-based integrity management systems can provide a solution to mitigating risk on bolted flanges, by providing traceability throughout joint life.

They go beyond leak prevention, to actively improve safety by demanding competent work throughout the process. They record the data permanently. This data is easily retrievable and it avoids the pile-up of storage boxes!

However, in Hydratight’s experience (we typically work on assets with 50,000-plus bolted joints) the installation of a proven software solution is only one element.

Furthermore, by working in partnership with Operators, it is possible to significantly reduce leaks. However, true Joint Integrity management isnot just something you can ‘buy’; it is something you must ‘buy’into.

Good systems are a partnership between contractors and operatorsand it is with the latter that Joint Integrity begins.

Hydratight are committed to improving the safety and integrity of all related assets. For the asset owners, this is good news – it also improves an asset's efficiency – and its bottom line!