When to specify tube to tubesheet joint mock-up test?

[srijey]

Are there any guidelines as to when a mock-up of tube to tubesheet joint would be recommended? Such an 'engineering judgement' is highly subjective, similar to defining what is 'critical'.

 

[EdStainless]

I would do it any time I was re-tubing an existing HX, or building a new one that isn't exactly like one that the fabricator has made recently.

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Plymouth Tube

 

[srijey]

Thank you Ed. In that case, for a new design, it's just an option for the operators? Higher alloy, high pressure, critical service are some of the terms I used to hear for specifying tube joint mock-up. There must be some international standard which recommends to perform Section IX QW 193. Strangely, Section IX QW 193 opening paragraph suggests same.

 

[metengr]

A tubesheet mock-up should be required regardless if new or re-tubing. The mock-up provides some level of assurance that the tube to tubesheet rolling procedures are sufficient and design. New products don't guarantee any better quality level in comparison to a retrofit. The decision for a mock-up is client driven and some construction codes require it to qualify tube to tubesheet strength welds.

 

[SNORGY]

I have had some experience with this.

A Vendor or Fabricator will typically have a tube rolling (expanding) procedure for each of or a number of combinations of tube to tube sheet joint designs. A mock-up and test would be specified for a joint configuration or detail that does not exactly fall within the parameters of the procedure. Say, for example, expanding a work-hardenable material into a close tolerance hole. The Vendor or Fabricator might have a procedure that specifies 8% to 10% tube wall reduction, but that might not apply in this case. Perhaps the optimum joint strength is achieved at 5% tube wall reduction. The mock-up and pull test could be used to find this out.

You also might want such a mock-up and test if the bundle experiences significant temperature differential between tube sheets or between passes in multiple pass exchangers.