UCS-66 (i)(4) 1

[jakov11000]

Hi, it looks like there is nothing about UCS-66 (i)(4) on the forum.

UCS-66 (i)(4) quote: "The MDMT adjustment as determined in (1) above may be used for impact tested welding procedures or production welds."

Does this mean that MDMT reduction Ratio (R) calculated for base material can be used to lower MDMT of the WPS? Lower than temperature at which the WPS is qualified by impact test?
Any interpretation on this?

As an example:
We perform impact test for WPS qualification on -20F and get the values as specified in UG-84. Then we calculate the ratio (R) for base material, let us assume 0.8. Read the MDMT reduction from figure UCS-66.1. It is 20 F for R=0.8. Now, our WPS can be used on -40F (-20F - 20F)?

Thank you!

 

[Geoff13]

The stress ratio is a "per component" evaluation, as noted in UCS-66(i). The WPS is not a component, so it can't be globally lowered by the Figure UCS-66.1 adjustment.

However if you have a specific component in your pressure vessel that has an MDMT of -40°F and a stress ratio of 0.8, then you could weld it with this -20°F WPS.

However the very next component in the vessel may have a higher stress ration, and you'll have to find a colder WPS to weld it with.

This will involve a complete understanding of the stress ratio of every component in the vessel under every design loading, and a lot of careful control of which WPS is used for each weld. A sharp AI will notice that you're using a -20°F WPS on a -40°F vessel, and will want to review all your stress ratio evaluations.

I'd just run a -40°F WPS and be able to use it for every component in the vessel.

 

[jakov11000]

Thank you Geoff13! Yes, this is for specific component. Is there an interpretation for this? To show it to the AI, if he asks for it.

Thanks!

 

[r6155]

@ Geoff13

Have you ever been present in the entire process that requires a CHARPY test?

What is your business if you can do the CHARPY test at -20ºF instead of -40ºF?

There is a lot of difference in the process during the laboratory test.

Low temperature charpy testing involves placing the charpy test specimen in a chamber bath of propylene glycol and dry ice until a calibrated thermocouple records the temperature required for the test.
Once a specimen reaches the precise temperature, it is quickly placed into a special holder in the test.

Regards

 

[Geoff13]

To r6155

The vast majority of tanks and pressure vessels we build are in northern Alberta (Canada) where the MDMT is usually specified as -40°F. As a result I see -40°F as the standard qualification temperature for WPS's, and no doubt that is reflected in my answer.

 

Maximizing the range of impact test temperature is one aspect of good welding procedure design. Within reason of course, because you can make almost anything pass in a one-off qualification, under conditions that range far from real fabrication conditions and materials.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."