Wait time between weld and NDT on boiler pipe (B31.1) 2-3days?

WHY DO SOME STANDARDS REQUIRE THAT YOU WAIT FOR A FEW DAYS TO INSPECT WELDS?
Most of welding standards include clauses such as:

CSA W59: Visual inspection and NDT of welded joints subject to high restraint and/or joints of quenched and tempered steels shall be delayed as long as practicable and preferably not less than 48 hours after completion of the welds.

AWS D1.1: Acceptance for ASTM A514, A517 and A709 Grade HPS 100W [690W] steels shall be based on NDT performed not less than 48 hours after completion of the welds.

This requirement is applicable when material is subject to cold cracking, also called Hydrogen Assisted Cold Cracking (HACC). This phenomenon is likely to happen several hours after welding is completed, when the weld and base metal have cooled to ambient temperature.

Regards

Some of the materials used in boiler tubing/piping are prone to delayed cracking without or before PWHT. But the Code does not require same. A number of engineering specs will requre a 48 to 72 hr hold time for specific low alloy steels before NDE.

Of personal note, we once had RT'd 20 welds in P11, 20" diameter piping prior to PWHT, requireing repairs to one weld. After PWHT was performed about a week after weld completion, RT was again performed and 9 of the 20 welds were found to be cracked.

op said:

pipe in a boiler, designed according to ASME B31.1 standards

Click to expand...

ASME B31.1 is for piping external to a boiler. inside a boiler the piping is designed and constructed to the ASME Boiler and Pressure Vessel code. See the following and the code for details.

Delayed hydrogen cracking can often be the result of not taking enough care with control of moisture in welding rods and shield gas.

A technical report "Evaluation of Necessary Delay Before Inspection for Hydrogen Cracks" was published in the Welding Research Supplement of Welding Journal, vol.82, no.11, Nov.2003, pp.321s-329s.