When faced with an opportunity to install a branch connection using the “hot tapping” technique, pipeline operating companies have a wide variety of choices when it comes to branch connection design and installation practices (e.g., welding procedure options) depending on the application. The objective of a recently-completed joint industry project (JIP) was to develop industry best practices for hot tap branch connections, including a compendium of properly qualified procedures, guidance pertaining to specification of branch connection design for specific applications, and guidance pertaining to related areas of concern for which there was not widespread agreement.
The core group of welding procedures that was developed and qualified for branch groove welds and sleeve fillet welds all involve the use of shielded metal arc welding (SMAW) and conventional low-hydrogen electrodes. There are applications for which other welding processes and consumables have advantages, so procedures for a broader range of applications were also developed and qualified. All of the procedures were qualified in accordance with the requirements of a range of relevant industry codes, including the Twenty-first Edition of API Standard 1104.
The various options for branch connection design include integrally-reinforced fittings (e.g., Weldolets®), fabricated branch connections, and full-encirclement pressurized tees (e.g., Stopple® fittings). Some designs are better suited to some applications than to others. The guidance for specifying branch connection designs focused on geometric parameters, such as branch diameter, header diameter, and branch-to-header diameter ratio. Several antiquated branch connection designs that should no longer be used were also identified.
The related areas of concern for which guidance was developed included the need for sleeve end fillet welds, burnthrough prediction for in-service welding on thin-wall pipelines, pressure limits/pressure reduction requirements, flow rate limits, heat-affected zone (HAZ) hardness limits, welder qualification requirements, branch connection location and fit-up, pipeline support requirements, branch connection welding sequence, preheating for in-service welds, fillet weld size requirements, extent of welding required for integrally-reinforced fittings, inspection/non-destructive testing (NDT) requirements, delay time prior to inspection for hydrogen cracking, pressure testing prior to tapping, and grouting of larger diameter, larger diameter-ratio branch connections. This guidance, along with the branch connection design guidance, was used to develop a generic company specification for installing hot tap branch connections in the field. The use of this guidance and the compendium of properly qualified welding procedures that was developed during the JIP will reduce the cost of installing hot tap branch connections, increase safety during installation, and increase the reliability of completed connections.