Hole tolerances and finishes

[DDS1]

I am currently working on a retro-fit of a calandria type evaporator. I am fast tracking the project and am wanting to get my preliminary design to fabricators for quotes. I have ordered a TEMA standards book to reference the information I need but want to send out prints before the book arrives and need some help.

I am looking for tube sheet hole tolerances and finishes to give the fabricator. The tubesheets are 1" thk SA-516-70. The tubes which are to be rolled into the tubesheets are 1 3/8" O.D. I have asked the fabricators for a 1.389" reamed hole (14 thousands over) with a tolerance of +000 and -.003. Is this to stringent? I could also use help with hole groove infomation and finish. The tube will be rolled into the tube sheets using standard tube expanding rollers.

As mentioned, I have ordered what I believe to be the necessary reference literature. I need help until that arrives. I can firm up the design if I decide to change something after I receive the standards. Its only preliminary pricing.

Thank you

DDS1

 

[rmw]

I am surprised that your fabricator does not have the information you need. If he is an experienced fabricator of Roberts calandria, he should have faced this situation before, and have his own standards, better or worse than TEMA. Some fabricators of shell and tube hx's have more stringent tolerances than TEMA tight, as TEMA tight have a "tight" hole tolerance, but allow a surprisingly large percentage of holes to be out of the so called "tight" tolerance range.

Unfortunately I do not have my tema book at my current location, but had it in my hands just before leaving my last location. I will look tomorrow, and if no one else has come to your rescue, will respond tomorrow.

rmw

 

[rmw]

Noting that my TEMA book is an older version, it has no values in the tables for 1-3/8 tubes. However, interpolating between 1-1/4", and 1-1/2", it appears that you have picked the appropriate values for for the hole size corresponding to the "special close fit" category. (I referred to it as "TEMA tight" in the earlier reply.) Your under tolerance is per the "tight" tolerance, but your over tolerance is more stringent. TEMA allows 0.003 over for both tube sizes mentioned above. TEMA special close fit also allows 4% of the holes to be 0.010" over tolerance, which is what I was referring to earlier.

Four percent of the holes in an average Roberts Calandria at 1-3/8" might not be a worry compared to 3000 holes in a large power plant heat exchanger.

My TEMA does not specify a surface finish for the holes, except to require it to be free of burrs, so a reamed hole should be OK. Remember that surface roughness made by drill flutes act like miniture grooves, giving the tube OD something to adhere to as it is expanded into the tubesheet.

The grooves are called for as two minimum, 1/8" wide, by 1/64" deep, with no surface finish given. My experience has taught me to break the sharp corner at the hole diameter of the groove to minimize the sharp surface at the corner, especially if the tube is a softer material than the steel tubesheet you called out. (I suspect copper am I right?)

If, on the other hand, the tube is a hard material, like a stainless or titanium, there is a strong case to be made that grooves can be detrimental to good tube to tubesheet joints. I rarely see them used when the tubes are of those materials, and I am talking about up to 5000 psi(g) applications.

That is all I can tell you at this time. If anyone else has more current data, please wade in on this.

rmw

 

[DDS1]

rmw,

I appreciate your taking the time to follow up as mentioned. I don't disagree with your first response that a "good" reputible shop would/should know the requested information. I however do not like to rely on the fabricator (which is a contractor) to provide such information (unless I have the upmost confindence in their abilities and know that there response is objective and not tailored to what they are facilitated to do) and therefore felt that unbiased professionals like yourself would be a viable alternative. But I did understand your point and it was well received.

As for your second post, as mentioned, I apprciate your following up. 1 3/8" tubes are not "off the shelf" and I am using them only becasue the client has them in stock. I havent heard the fabricators yelp over my specs but your information is useful to help me "wing it" until my TEMA book arrives. Oh yea, they are stainless tubes and there are approx. 4000 of them. Thanks again.

DDS1