We use cookies to help you navigate efficiently and perform certain functions. You will find detailed information about all cookies under each consent category below.
The cookies that are categorized as "Necessary" are stored on your browser as they are essential for enabling the basic functionalities of the site. ...
Necessary cookies are required to enable the basic features of this site, such as providing secure log-in or adjusting your consent preferences. These cookies do not store any personally identifiable data.
Functional cookies help perform certain functionalities like sharing the content of the website on social media platforms, collecting feedback, and other third-party features.
Analytical cookies are used to understand how visitors interact with the website. These cookies help provide information on metrics such as the number of visitors, bounce rate, traffic source, etc.
Performance cookies are used to understand and analyze the key performance indexes of the website which helps in delivering a better user experience for the visitors.
Advertisement cookies are used to provide visitors with customized advertisements based on the pages you visited previously and to analyze the effectiveness of the ad campaigns.
In a Technical Paper Written by Dr Barbara K Henon of AMI Arc Machines Inc , entitled “Orbital Welding of Corrosion Resistant Materials” Section 3.5 Discolouration/Heat Tint, she laid out details of standards relating to weld purging in the Bio/Pharm/semi-conductor Industries.
She states that “Proper inert gas purging to prevent the formation of heat tint during welding is critical to maintaining corrosion resistance of 316L”. This of course, applies to all of the stainless and duplex steels as well as with titanium, zircalloy and nickel alloys.
The BPE standard specifies colour free welds referencing the colour chart of AWS D18
.
Readers wishing to have a copy of that colour chart, along with those of other standards e.g. Den Norsk Veritas, can contact rasewell@huntingdonfusion.com.
It is also noted that welds in the pharmaceutical industry are put into service in the ‘as welded condition’, not permitting any cleaning.
This stresses the need for an excellent weld purging technique that can only be achieved buy using a “Weld Purge Monitor®” that will indicate accurately down to 50 parts per million of oxygen.
The PurgEye® 300 Nano is a typical instrument to carry out these measurements and is in fact the lowest priced Weld Purge Monitor® able to read accurately down to 10 ppm
.
Passivation with nitric or citric acid-based solutions may be carried out, however that does not remove heat tint that can extend below the surface where it is not affected by passivation.
Dr Henon goes on to state that “achieving an adequate i.d. Purge with minimal heat tint discolouration helps to retain the corrosion resistance of the material during welding”.
A really adequate oxygen level for this is below 50 ppm