What About Interpass Temps? 2

tc7;
Interpass temperature is usually the temperature range between minimum preheat and some maximum temperature to avoid having the base material reach a temperature away from the weld that could affect mechanical or corrosion properties. The concerns for too much heat relate to possible changes in the base material corrosion resistance from sensitization (for austenitic stainless steels) and softening of low alloy steels from original heat treatment.

So, selection of the maximum interpass temeprature is specific to the materials that are joined.

Excellent answer metengr.

To add to your reply;
If the temperature of the base metal approaches the maximum interpass temperature, welding operations cease until the temperature of the base metal drops below the maximum IPT.

In some cases the interpass temperature has little detrimental affect on the base metal. In the case of carbon steel the interpass temperature isn't usually a concern unless notch toughness requirements are invoked. Q&T steels have IPT that must be controlled to avoid a loss of strength in the HAZ.

In the case of heat treatable aluminum alloy, they can be overaged if held at high temperatures for too long a period of time. Cooling with a "blower" can be helpful to minimize the affects of high temperature.

Different welding standards provide some direction as to when IPT must be considered and what the max. IPT is. In other cases the manufacture should be consulted. Many have websites that provide good information.

Best regards - Al

API RP 582 will guide you on typical maximum interpass temperatures. Then, the next question for us to debate is how, or more specifically where in the weld zone, does one measure interpass temperature.

Steve Jones
Materials & Corrosion Engineer

There is no debate,
ISO 13916 Welding - Guidance on the Measurement of Preheating Temperature, Interpass Temperature and Preheat Maintenance Temperature First Edition

So then in reading between the lines on all the above, I'm thinking that interpass wants to be limited and monitored because too high of a dT between the weld area and the cold areas creates a quenching effect and is why low carbon steels do not have a concern with controlling IPT? Does that about summarize it?

Then with no access to API RP 582 as suggested by Steve, or any other specific guidance can I just arbitrarily set IPT to, say 300 deg F above preheat BUT not to exceed, say 500 deg F as a universal shop practice and be happy about it?

Thanks.

tc7;

I'm thinking that interpass wants to be limited and monitored because too high of a dT between the weld area and the cold areas creates a quenching effect and is why low carbon steels do not have a concern with controlling IPT?

Click to expand...

No, not exactly. The maximum interpass temperature is selected to avoid putting too much heat into the weld and surrounding base metal that will affect properties, and create more distortion.

For example, carbon steel with no special heat treatment to the base metal, the maximum interpass temperature is based on balancing arc time with reducing distortion by placing too much heat into the weld region.

Metengr

I'm fully with you on ISO 13916 - I was waiting for someone to take the bait and say something like 50 mm from the bevel! Application of ISO 13916 will come as a great shock to the 'Tempilstik Brigade' when the owner's engineer tells them no way can the weld zone be contaminated with crayon residue.

Steve Jones
Materials & Corrosion Engineer