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REQUIREMENTS FOR LOW ALLOY STEEL PIPING ATTACHMENT WELDS

Proper design and fabrication, heat treatment and inspection practices play a vital role in achieving good quality and performance of low alloy steel piping. These materials have narrower fabrication windows as the alloy content goes up and non-adherence to correct execution practices may lead to leakage by delayed hydrogen cracking, stress corrosion cracking or fatigue resulting in unplanned shutdowns and costly repairs.
This paper describes details about strengths and weaknesses of support design and fabrication practices for such attachment welds. The paper discusses various precautions to be taken during the design and fabrication stages for low alloy steel supports attachment welds. It will discuss heat treatment cycles viz. preheat, interpass, dehydrogenation treatment (post heating) and post weld heat treatment (PWHT). The control of consumables, welding environment conditions, and the weld heating cycle is essential to prevent hydrogen assisted cold cracking in high hardness microstructures in weld and HAZ, and for achieving successful relief of residual welding stresses.

Product Number: MPWT19-15315
Author: Ameer Hamza, Jignesh Desai, Jan-Willem Rensman, Mark Van Den Broek, Kuntak Daru
Publication Date: 2019
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Role of Non-Metallic Inclusions and the Microstructure Constituents on HIC Performance

Product Number: MPWT19-14439
Author: Amro Al-Hattab1,Diaa Elsanosy2, Gaurav Tomer3, Abdullah Al-Jarbou4
Publication Date: 2019
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With increasing oil & gas demand and depletion of sweet reserves, oil & gas companies in the regional
economies are focusing towards the exploitation of sour resources. This necessitates the use of pipelines
and down-hole tubing made from special steels with significant resistance to hydrogen-induced cracking
(HIC). These steels are produced through specific technologies for enhanced chemical composition control
and microstructural engineering to incorporate the required strength, weld ability and improved HIC
resistance. It is well established that the HIC initiates at sites with microstructural heterogeneities whether
due to presence of gross nonmetallic inclusions or the micro-structural constituents. The presence of central
segregation further aggravates the conditions particularly when the final pipe sizes require the longitudinal
slitting of the coils. Presence of non-metallic inclusions in the steel makes it vulnerable to hydrogen-induced
cracking under wet H2S environment. The mechanism of HIC begins with the generation of hydrogen atoms
by corrosion reaction of H2S and Fe in the presence of free water. The hydrogen atoms then diffuse into
steel and accumulate around the inclusions. The higher number of inclusions equates to the more sites
available for hydrogen adsorption. Recombination of hydrogen atoms to H2 molecules builds up a heavy
gas pressure in the interface between matrix and inclusions. Cracking initiates because of the tensile stress
field caused by hydrogen gas pressure and crack propagates in the surrounding steel matrix. The
longitudinal slitting exposes the internal microstructural abnormalities to the skelp edges which are then
incorporated in the thermally stressed weld zone. While the post-weld heat treatment (PWHT) mostly
homogenizes the weld zone microstructure, the presence of excessive central line features cannot be
completely removed thereby making this zone more prone to HIC attack

Picture for The Sensitisation Behaviour of Alloy UNS N08825 After Heat Treatment as Used in Clad Materials
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The Sensitisation Behaviour of Alloy UNS N08825 After Heat Treatment as Used in Clad Materials

Product Number: 51317--9459-SG
ISBN: 9459 2017 CP
Author: Helena Alves
Publication Date: 2017
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The aim of this paper is to present recent standard test corrosion data obtained in laboratory for alloy UNS N08825 after post weld heat treatment in comparison with as delivered (soft annealed) material.

 

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51318-10588-Corrosion Resistance of Roll-Bonded Clad Plates for Oil & Gas Applications

Product Number: 51318-10588-SG
Author: Sandra Le Manchet / Bastien Chareyre / Cédric Chauvy / Sarata Cissé
Publication Date: 2018
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