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A Study on Test Pressures for Hot Tap for Large Diameter Pipes

[+] Author Affiliations
Subrata Saha, Abhijit Pisal

Piping, Reliance Engineering Group RCITPL, Jamnagar, Gujarat, India

Paper No. IOGPC2015-7903, pp. V001T01A001; 5 pages
  • ASME 2015 India International Oil and Gas Pipeline Conference
  • ASME 2015 India International Oil and Gas Pipeline Conference
  • New Delhi, India, April 17–18, 2015
  • Conference Sponsors: Pipeline Systems Division
  • ISBN: 978-0-7918-5646-8
  • Copyright © 2015 by ASME


Hot tapping [1–3] is the operation which allows attaching new branch connection on piping system and pipelines containing hydrocarbons under operating conditions. This operation is associated with high level of risk and is undertaken with extreme caution.

A major source of risk from the point of structural integrity is the low limits on value of test pressure as compared to the Code specified test pressures [4]. The reason is pipes are not designed for external pressure and they may “buckle” under external pressure during testing. The current practice is to use curves which are specifically developed by various operating companies [3] and are not generally available in the public domain. The problem becomes severe for large diameter thin pipes where the safe test pressure becomes quite low. This has potential risk as the pressures could be much lower than the operating pressures.

This paper discusses this problem and also details out an analytical method which can be used to obtain higher “Strength test pressure” with respect to ratio of parent pipe diameter and thickness. So that design reliability of the hot tap branch can be increased. Methodology explained in paper gives lot of flexibility to go for higher test pressure. FEA analysis is used to demonstrate these results.

Globally acceptable procedures also advocate using FEM analysis to confirm the strength test pressure. Based on that FEA analysis was done and it is established that hot tap design can sustain higher test pressure than operating. In reality Hot Taps have been performed and tested successfully with the test pressures as per our proposed method which in a way validates our theory.

Copyright © 2015 by ASME
Topics: Pipes



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