We are designing one S&T heat exchanger with Carbon Steel MOC.
The Design MDMT for shell side is -29 degree C.

Tubesheet MOC is SA 266 Gr. 2 & its thickness is 67mm.

We can not take Impact Testing exemption as per UG-20(f) as specified in the project documents.
When we designed the heat exchanger in COMPRESS we found that it is not considering reduction in rated MDMT for Tubesheet as per Fig. UCS-66.1.

However, the same is being considered for body flanges with same MOC SA 266 Gr. 2.

I shall be thankful if you kindly inform why COMPRESS is not considering reduction in rated MDMT for Tubesheet as per Fig. UCS-66.1?

Please let me know the type of HE and size. I will cross check in PV ELITE

Thanks brkmech1234.

I am attaching the COMPRESS Design file herewith.

• http://files.engineering.com/getfile.aspx?folder=8f139970-5c23-4951-b427-e7

Also find the Design Calsulation Output in PDF format.

• http://files.engineering.com/getfile.aspx?folder=ea84144a-d6dc-463e-b81a-a0

I have checked and found that curve selected for this material is B. If you provide a normalized material and produce it to fine grain practice, the curve will become C and new MDMT is -31 deg C which is below the requirement

Cheers

Noted & thanks for your reply.

Our Tubesheet MOC is not normalized & falling under Curve B.

However, my query was why COMPRESS is not considering reduction in rated MDMT for Tubesheet as per Fig. UCS-66.1.

Because if it considers this exemption, there will not be any requirement of normalizing & fine rain practice.

That is because minimum required thickness of tubesheet is very less as compared to provided thickness.

Here, we need to provide higher thickness for tubesheet so as to accommodate collar bolt arrangement as per API 660.

Your flange is exempted by UCS-66(b)(1)(b) considering coincident ratio.

Thanks brkmech1234!

Noted that in our case flange is exempted.

However, My query was regarding Tubesheet.

I wish to know why COMPRESS is not considering reduction in rated MDMT for Tubesheet as per Fig. UCS-66.1.

I guess the following is the reason. The calculations flange is very easy compared to tube sheet and software easily back calculate the required thickness and there by coincident ratio. The same thing may not be easy for tube sheet. Same thing you can raise it to compress

Thanks brkmech1234. I will.