Are there any requirements for the nuts used on heat exchanger tie rods?
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For the nuts on the heat exchanger tie rods, should the standard GB/T41 (grade 5, tolerance 7H) be used or GB/T6170 (grade 6, tolerance 6H)?
1. Height of the tie rod nut — it must be high enough to accommodate the length of the tie rod and the thickness of the heat exchanger； 2. Nut material – generally 304 stainless steel or copper is used ； 3. Structure — Compared to solid nuts, thin-walled nuts take up less space and allow for a greater degree of compression, enabling them to fix the tie rods to the heat exchanger more effectively ； 4. Other considerations — the two nut lugs should be as close together as possible to achieve the best fixing effect.
Fasteners for pressure vessel flanges should comply with NB/T 47027-2012 standards. The nuts used for pressure vessel flanges are one size larger than the hexagonal nuts specified in GB6175/6170. If there are special requirements regarding the medium used in your heat exchanger, it is advisable to avoid using conventional nuts
Both GB/T41 and GB/T6170 are acceptable; if the tie rod is made of carbon steel, a grade 5 nut is sufficient. If the tie rod is made of stainless steel, then choose nuts of the same material. There’s no need to worry too much about nut strength.