Learnings

Outcomes

A key aspect that National Grid wanted to explore was the opportunity to use, where viable, inline isolation tools for onshore pipeline use. Such tools propose to provide a non-intrusive method to interrupt product flow and isolate pipeline sections which require repair or maintenance, removing the necessity to perform hot work on a live pipeline. Product flow in the pipeline is halted through the use of an expanding packer to seal in the pressure and a series of mechanical grips to maintain the necessary resistive force and prevent tool slippage. The technology has been used commercially offshore, however offshore pipelines are designed with higher wall thicknesses, such that the pipe-wall stresses induced by the tools when active remain acceptable. The acceptability of the tools for thin-walled onshore pipeline use has not yet been confirmed. 

With a significant volume of remedial work planned on the NTS, particularly associated with valves and isolation joints, inline isolation tools potentially provide considerable benefit (carbon footprint and financial). If the technology can be verified for onshore use, it could be considered the preferred method for pipeline maintenance going forward. 
Research has been completed into the use of inline isolation tools for onshore pipelines by the Pipeline Research Council International (PRCI) and this project looked to extend PRCI’s work further. This report presents a series of studies completed by Pipeline Integrity Engineers Ltd. (PIE) which are aimed at understanding the current range of inline isolation tools and their applicability for use on National Grid pipelines; and assessing the potential impact inline isolation tool operation would have on National Grid’s policies and procedures. 

The conclusions of the studies are: 

State of the art review 

Review of in-line isolation technologies (assessment of vendor techniques, capabilities, limitations, operational parameters etc) including PRCI tool review report 

PRCI research into the onshore use of inline isolation tools indicated that inline isolation tools from three different manufacturers can be used to isolate a 610 mm diameter, 9.525 mm wall thickness, grade X70 pipe at 108.6 barg pressure, under laboratory conditions, for a period of 2 hours, with no slippage of the tool or leaks past the pressure seal. Additionally, there was no plastic deformation of the pipe recorded. 

The PRCI research however left a number of questions unanswered, which require further consideration before the tools can be considered validated for onshore use. These include demonstration of the tools outside of laboratory conditions, focus on stresses during and after application, presence of internal damage and any impact to fatigue life. These unanswered questions would be covered in any trial of the tool, either offline, online or both. 
 
Determine NGGT requirements 

Assess NG potential requirements for in-line isolation – diameters / grades / wall thickness’s / pressures / number of applications etc. 

Based on the scenario detailed in the scope of this report, various isolation joints (IJs) on the network have been highlighted as requiring maintenance. In order to complete this maintenance, outages are required which have financial and environmental impacts. Each of these locations were reviewed as part of this project and the inline isolation tool vendors; T.D. Williamson and STATS tools were reviewed with respect to these locations. It was determined that, in-principle, both vendors have the capability to isolate all locations, however the use of additional external reinforcement may be required in some cases depending on the vendor and the pipeline section. 
 
Vendor vs NG assessments 

Compare and contrast (1) and (2) to identify where overlaps exist and what would be required from the vendors to address any gaps. 

A review was conducted by PIE of the capabilities of inline isolation tool vendors with respect to National Grid’s initial requirements. PIE undertook conversations with both TDW and STATS group. Contact with the third company involved in the reviewed PRCI report, PPIG, was also considered, however no evidence of operations outside the USA could be found and no global offices uncovered. It was determined that an exclusively USA based company would not be of benefit to National Grid and their UK operations. 

Both vendors were requested by e-mail to answer a simple set of questions based on National Grid’s initial data requirements. The vendors replied and agreed to further interrogation through online meetings. Both vendors were accommodating and appeared open regarding their respective tool capabilities.  

Neither vendor was disqualified from the process or demonstrated that they would not be of use within National Grid’s requirements. However, it was stated that for each proposed tool operation a pipeline specific review would be required to assess suitability for tool deployment. This would appear to be good practice and PIE can see no reason for this not to be accepted as standard. Tool deployment is essentially the same as the launch of an inline inspection tool and therefore carries the same risks. Treating each deployment in the same way as an inline inspection tool would help manage and mitigate the risk of not only the launch and recovery, but deployment (locking and pressure control) on the pipeline’s integrity. 
Whilst tools from both vendors appear to be of use for National Grid assets, the STATS tool and its variants do appear to give (through the umbilical and stem tooling) a more controlled and therefore risk reduced deployment should the tool be needed near launch/recovery installations. 

One area of concern that has developed, is a suggestion made by the vendors that external reinforcement may be required across some of the assets during tool operation. Further clarification from both vendors is needed and more off-field investigative testing may be necessary to understand which National Grid assets will fall under this requirement. 
 
NGGT policy / procedure impact assessment 

Use output from (3) to assess impact on NGGT Policies and Procedures (but not drafting at this stage) – which documents would be affected and to what degree, identify any new documentation requirements, etc. High level impact assessment on NGGT policies and procedures 

The impact of inline isolation tool operation on the NTS to National Grid’s policies and procedure documents is minimal, with the update of only a small number of sections being required. It is noted however that some sections will require further review after a field trial has taken place. 
 
Draft NGGT policy / procedure for inline isolation 

Document functional requirements for In Line isolation assessment and procedure for application. Amend existing documentation or draft standalone document  

This work package was not carried out as the outcomes of the field trials is needed to fully develop the text needed for the policy and procedure updates. 
 
Field trial requirements 

Given the pipeline sections containing the insulation joints identified by National Grid as requiring repair are representative of the whole NTS network, each of the joints may be considered a suitable location for an online field trial. The field trail location should be selected from these by National Grid based upon their own priorities. All things being equal, a pipeline section with diameter of 914.4 mm should be selected as this is the predominant diameter in the NTS network.

Lessons Learnt

This project was planned well to cover a lot of content over a short time frame. Communication was key to ensure delivery in the time frame. Regular meetings were held monthly and where required, adhoc calls were arranged by-weekly.  
The concept of inline isolation, whilst carried out extensively offshore has some key challenges onshore, most notably how the tool can be stopped in position using flow controls.