The Validation Centre (TVC) Ltd

The Validation Centre (TVC) Ltd

Purging Manual Tie-In Welds on Pipe Spools with Wireless Remote

October 8, 2020

Purging Manual Tie-In Welds on Pipe Spools with Wireless Remote

TVC was approached by an offshore oil and gas pipeline fabrication company to assist with purging manual tie-in welds on 1 Km duplex and Inconel clad pipe spools. The welding specification stated:

• the internal back purge had to be maintained for the root, as well as the hot pass
• the level had to be less than 50ppm

The client had previously been using an internal purge dam with an external purge O2 monitor; however, this was not a suitable solution because they had to test the O2 content through the open root gap. This meant that they were unable to monitor and verify the O2 levels as stated in the welding specification when closing the root pass and whilst welding the hot pass. Another issue was the time taken to purge the joint as they were supplying the purge gas from the open end of the pipe over 1 Km; even with an initial flow rate of 40 LPM, the preliminary purge took considerable time.

Designing Solutions

TVC provided a solution for all the client’s issues by designing and supplying a self-contained, wireless remotely operated purge system. This system was the first of its type ever used in the field and comprised of:

• a remotely controlled, battery-powered internal stainless steel purge dam with silicon high-temperature inflatable bladders
• a zirconia high-resolution Oxygen sensor
• a 3-stage automatic purge gas flow control
• an onboard Argon purge gas reservoir

Purge_Dam

Purge Dam

Purge_Dam_Pipe

Purge Dam in Pipe

How the System Operates

The system operates as follows:

  1. A stainless steel draw wire is deployed through the 1 Km spool. The two spool pipes are lined up and the purge dam and gas reservoir are placed inside the open pipe directly at the tie-in weld location and attached to the stainless steel draw wire. The two pipes are then aligned using an external clamp for manual 5G welding operations. A Wi-Fi repeater module is placed at the open end of the 1 Km spool.
  2. Once the pipes are ready to weld, the Welding Inspector or operator uses the hand-held remote control to start the purging process. A wireless signal is sent from the external welding position and is transmitted along the pipe to the internal purge dam via the Wi-Fi repeater. The total transmission length of the signal is 2 Km.
  3. When started, the purge gas from the gas reservoir is used to inflate the silicon bladders. Using pressure sensors fitted to each bladder, the system can sense when the bladders are fully inflated. The system continually monitors the bladder pressure and will automatically top them up if the pressure should start to drop, ensuring that a seal is continually maintained. Once fully inflated, a bypass valve is opened, and the purge gas flow will flow at the high flow level. The flow level can be pre-set from 5 to 50 LPM, purging the internal area between the two bladders.
Purge_Dam_Bladders

Purge Dam Bladders

Flow Limit Control

The system has two pre-programmed limits to control the gas flow. When above the High limit, the Purge Gas flow will be at the highest flow rate (adjustable from 5 to 80 LPM) to enable rapid purging. An audio/visual traffic light alarm system can also be used externally in conjunction with the 3-stage automatic gas flow control to show the system status. When the O2 level is above the High limit, the traffic light is red. When the O2 level drops below the pre-programmed High limit, the purge flow will automatically drop to the pre-set pre-welding flow rate, typically about 20 LPM, and the traffic light will turn yellow.

Once the O2 level drops below the Low limit, typically set at 50ppm, the flow will again automatically reduce to a low level to allow welding to start. The traffic light will turn green, indicating that it is safe to start welding. A dwell time can also be pre-programmed so there is a delay when changing between limit states to ensure that the purge level has fully stabilised below the required welding level.

When the green light is activated, the welding process can start, however, during welding the system constantly monitors and logs the O2 levels. If the O2 level should approach the Low limit, the audible alarm will sound on the external traffic light alarm warning the welder to immediately stop welding. The system will then automatically increase the purge gas flow to control the O2 level and when the O2 level drops back below Low limit, the green traffic light will illuminate again indicating that the welder can re-start.

Remote_Hand_Controller

Remote Hand Controller

Traffic_Light_Visual_Audible_Alarm_Beacon

Traffic Light Visual/Audible Alarm Beacon

Root Pass Purge Flow Reduction Solutions

When the root pass is nearing completion, the purge flow needs to be reduced to allow the closeout of the root weld. A solution for this has been built into the system – when a button is pressed on the remote control unit the internal purge gas flow is reduced to a pre-set extra low flow which is suitable for the closeout of the root weld to take place.

The purge flow and O2 monitoring can be left to continue for the completion of the hot pass and any other subsequent fill passes. Once purging is no longer required, the purge flow can be stopped remotely, and the bladders deflated. With the bladders deflated, the purge dam will rest on small stainless steel wheels and the purge dam and gas reservoir can be removed from the pipe using a winch system attached to the stainless steel draw wire.

Onboard Data-Logging

The system has onboard data-logging and so the full operation, including O2 levels and flow rates, can be recorded from the start of the purging process to completion.

Our technology has provided our client with a solution to all their purging issues and is suitable for the manual tie-in welds in pipeline fabrication, both onshore and offshore. If you have an application that could benefit from this technology, then please do not hesitate to contact us to discuss your requirements.