Here are Examples of Typical Orbital Welds for a Biopharm System We are Building in our Shop. The Weld Discoloration has been Removed from the OD

Joining sanitary stainless steel fittings and tubing by means of computerized orbital welders has become increasingly commonplace in the sanitary process industry.  This method has become the standard for the biopharmaceutical industry and the more recent versions of the 3A standards allow orbital welds in dairy process systems.  Traditionally, 3A requirements dictated all welds to be mechanically polished on the ID of a process line.  Now they accept “as is” orbital welds.

Orbital welding machines are unique in that fittings to be joined are fixed into a weld head.  The weld tungsten then travels around the fixed fittings to affect the weld.  Because of this, they require longer tangent fittings than traditional weld fittings so they can fit in the machine.  The ASME BPE standards addressed this issue by developing a set of standardized fitting dimensions, all with tangent lengths of at least 1 ½” long.  They also standardized on required surface finish levels.  So today there are commercially available fittings available on the marketplace that specifically meet the ASME BPE requirements.  But BPE fittings normally have surface finishes well beyond what in required in the food, dairy and beverage industry.  They are priced at a premium compared to standard sanitary weld fittings and are available in 316L stainless only, not 304.

So if you are putting together sanitary process lines that don’t require BPE type surface finishes or merely require 304 stainless steel do have to use ASME PBE fittings if you want orbital welds?  Often not.  We have studied standard sanitary weld fittings and hope to bring some clarity as to their suitability to be orbitally welded.

AMI 800 Series Narrow Weld Head

We make hundreds of sanitary welds in our fab shop every week, some with orbital welders, some hand welds and some with semi-automatic machines.  Most of our orbital weld machines are AMI model 207 with the 8 series narrow heads.  These are very common in the sanitary process industry.  Our welders say they need 1” of straight tangent on each fitting to fit into the machine, but they might be able to get by with 7/8” in a pinch.  We do have some narrow head welds that allow us to get down to ¾”.

So where does that leave traditional sanitary fittings as far as their ability to fit into an orbital weld head?  It depends on the size.  We looked at both standard tees and elbows and came up with the following using standard Waukesha sanitary weld fittings:

2″ Elbows, one ASME BPE, one traditional Sanitary. They have the same radius but different length tangents

Looking at this table, 1” and 1 ½” fittings look to not have enough tangent to be orbitally welded.  But, 2” and above should work fine with the AMI narrow head welder.  Of course if you are just joining two straight pieces of sanitary tubing, there are no issues at all.  Also the standard L14AM7 weld ferrule, which is 1 1/8” long, is a tight fit but will gives us just enough length to fit into one our weld heads.  As far as reducers, their tangent lengths are all over the map and you have look at them one size at a time.

There is another trick of the trade that may help you in some situations.  Our welders, who are highly skilled, have developed the ability to use orbital weld machines and only fix the collet on one side of the joint to be welded.  That allows them to join fittings where one has a 1” plus tangent length and the other is much shorter. Contact us if you want some advice on this.  We would be happy to share our knowledge.

AMI 207 Welder

In conclusion, if you are assembling a sanitary process system and want the integrity and consistency of orbital welds, but don’t want to pay the premium price of using ASME fittings, you can often use standard sanitary fittings without a problem.  You just have to do your homework first.  If you want to put together a sanitary process line but don’t want the hassle of welding it at all, contact us.  We can talk about ways we could pre-fabricate most or all of the entire system for you.  We will discuss that topic in more detail in future blogs.