Page 11 - Hot Tapping - CCPS Safe Work Practice

Strategies and Effective Practices

to Manage and Mitigate Hazards

Making sure that metallurgy of the existing pipe is suitable for hot tapping.
g Hot tapping is most commonly performed on carbon steel piping and equipment.
g Where hot tapping is performed on ferritic alloy (stainless) steels, additional specialized procedures which address
preheat, post-heat and post-weld heat treatment are required.
g Hot Tapping on metallurgies other than carbon steel requires special procedures and is outside the scope of this document.
g Positive Material Identification (PMI) on the pipeline / equipment is necessary where hot tapping is to be done.
g If there are welding joints that intersect hot taps, then PMI should also be done on the weld joints
g Hot Tap welding should not intersect with an electric resistance seam weld in the pipe.

Inspect the existing weld joints that intersect the hot tap weld joint for integrity.
g Hot Tap should be avoided on existing weld joints. The location should be chosen in such a way that Hot Tap
welding does not interfere with the existing weld joints.
g Longitudinal seam weld joints should be identified by suitable in-situ etching methods.
g If Hot Tap cannot be avoided without intersecting a weld joint, then the interfering weld joint should be
volumetrically inspected (either UT or RT) to make sure that there are no defects in the weld joint that can lead to
burn through during hot tap welding. The UT or RT should be done for the purpose of hot tapping and certified.
g The area over which hot tapping is to be done should also be checked by the Mechanical Integrity inspector to
detect sub-surface defects, if any.

Making sure that the metal thickness at the hot tap location is adequate.
g The location where thickness is to be measured should be hard punched (using a metal punch rather than drilling a
hole) so as not to change the character of the metal prior to inspection. This location must not be changed without
the consent of the site inspectors.
g Thickness should be measured by devices that work based on Ultrasound. Any other method of measurement
needs to be approved by the owner’s inspector.
g The thickness should be exactly measured at the location where the welding is expected to be done. It is
recommended to measure thickness over a 50 mm (2 inch) band. Recommended minimum thickness for hot
tapping is about 5.0 mm.
g A critical review of the measured thickness may be necessary if:
a) Hot tapping welding is planned on systems with thickness close to the minimum thickness of 5.0 mm
b) Hot tapping is being considered on corroded pipelines. (e.g., Nominal thickness is 10 mm and measured
thickness is close to minimum required thickness of 5.0 mm)
c) Hot tapping is planned on a system which has undergone a fitness for service evaluation
g High Temperature thickness measurement should be cross verified adequately to ensure that the measured
readings are dependable
g Making sure that the metal where hot tapping is being done meets the hardness requirements.
g It is recommended to measure and certify hardness to be less than 200 BHN (Brinell Hardness Number). Higher
hardness material can crack during welding. Higher hardness can also cause problems during drilling of coupons.

SAFE WORK PRACTICE, HOT TAPPING 8