tubes. Each tube is sealed on its own into a PTFE tube sheet with PTFE sockets and packing. That single detail matters more than most buyers realise. If one tube cracks, you pull that tube and replace it. You don\u2019t retube the whole bundle.<\/span><\/p>\nHere\u2019s what the standard Goel Impex range handles:<\/span><\/p>\n\n- \u00a0 \u00a0 <\/span>Temperatures from -40\u00b0C to 150\u00b0C on both shell and tube side, with up to a 120\u00b0C difference between the two sides<\/span><\/li>\n
- \u00a0 \u00a0 <\/span>Full vacuum on both sides, in every size<\/span><\/li>\n
- \u00a0 \u00a0 <\/span>Heat transfer areas from 3 m\u00b2 to 25 m\u00b2, built with 37, 73, or 151 tubes depending on shell size (DN 150, 225, or 300)<\/span><\/li>\n<\/ul>\n
For bigger duties, we build custom units well beyond that. Our manufacturing arm, Goel Scientific Glass Works Ltd., has supplied glass heat exchangers up to 50 m\u00b2.<\/span><\/p>\nThen there\u2019s visibility, which sounds like a small thing on a spec sheet. On a night shift, being able to see condensation, fouling, or a colour change inside the exchanger saves a lot of guesswork.<\/span><\/p>\n![\"PTFE](\"https:\/\/goelequipments.com\/blog\/wp-content\/uploads\/2026\/09\/ptfe-tube-sheet-glass-shell-and-tube-heat-exchanger.png\" "\\"PTFE")
<\/p>\n
<\/span>Where Glass Is the Wrong Choice<\/b><\/span><\/h3>\nKeep glass away from hydrofluoric acid and fluoride-bearing streams. The same goes for hot concentrated caustic and hot concentrated phosphoric acid. Glass also isn\u2019t meant for duties above 150\u00b0C or for high pressure. If your process sits in that list, no glass supplier should be quoting you.<\/span><\/p>\nIf your duty sits comfortably inside glass\u2019s limits, though, paying several times more for SiC mostly buys peace of mind you don\u2019t need.<\/span><\/p>\n<\/span>Graphite Heat Exchanger: Strong With HF and Phosphoric Acid, Weak With Oxidizers<\/b><\/span><\/h2>\nResin-impregnated graphite has been the workhorse of acid plants for decades. A graphite shell and tube heat exchanger conducts heat well and handles hydrochloric acid, dilute sulphuric acid, hydrofluoric acid and hot phosphoric acid without much trouble. Mersen, one of the largest graphite exchanger makers, says it has supplied the largest units for the biggest greenfield phosphoric acid projects in the world. That\u2019s the duty where graphite earns its place.<\/span><\/p>\nThe problems start with oxidising media. Mersen’s own data rates its standard phenolic-impregnated grade as having limited resistance to nitric acid, chlorine, bromine and bases, with a maximum design temperature of 200\u00b0C. PTFE-impregnated grades cope better with mildly oxidising media, but they cost more. Those oxidising duties are exactly where glass is at its best. Graphite doesn\u2019t forgive water hammer or careless handling either, and you lose all visibility into the process.<\/span><\/p>\nOur view is simple. If your stream contains fluorides or hot phosphoric acid, graphite is a sensible and proven choice. For most other acid duties, it\u2019s worth checking whether glass would do the job for less.<\/span><\/p>\n<\/span>Silicon Carbide (SiC) Heat Exchanger: The Best Material on Paper, and the Priciest<\/b><\/span><\/h2>\nSiC is the material glass engineers quietly admire. Pfaudler describes it as having corrosion resistance similar to glass with far better heat conduction. That\u2019s a fair summary.<\/span><\/p>\nA SiC heat exchanger also handles more pressure and heat. SGL Carbon\u2019s SiC shell and tube units, for example, have a standard design temperature of 180\u00b0C (up to 220\u00b0C) and a design pressure of 8 barg (up to 10 barg), about 8.2 to 10.2 kg\/cm\u00b2(g). CG Thermal\u2019s design with PTFE tube sheets goes up to 150 psig at 400\u00b0F (about 10.5 kg\/cm\u00b2(g) at 204\u00b0C).<\/span><\/p>\nSo why doesn\u2019t everyone buy SiC? Price, mostly. A SiC unit usually costs several times more than a glass unit of the same area, and lead times can be longer. The grade matters as well. Directly sintered SiC resists HF, while grades that contain free silicon do not, so always ask for the exact grade before ordering for fluoride service.<\/span><\/p>\n<\/span>Does SiC Really Transfer Heat Much Better Than Glass?<\/b><\/span><\/h2>\nIt depends on the duty, and this is where a lot of sales pitches get slippery.<\/span><\/p>\n<\/span>Gas Cooling<\/b><\/span><\/h3>\nHere the gas-side film limits heat transfer, and the tube wall barely matters. A pilot plant study comparing SiC and glass tubes in air cooling expected only a 3.8 to 5.4% gain from SiC\u2019s higher conductivity. The measured gain was 18 to 22%, but the extra came from the rougher SiC surface, which also raised the air pressure drop by 17 to 24%. For gas duties, glass performs much closer to SiC than the conductivity numbers suggest.<\/span><\/p>\n<\/span>Condensing and Liquid-to-Liquid Duties<\/b><\/span><\/h3>\nHere the story changes. The glass wall is a real part of the resistance, and SiC or graphite can reach noticeably higher heat transfer coefficients. For reference, the glass units we build typically reach 410 to 640 W\/m\u00b2K for steam-water condensation and 290 to 410 W\/m\u00b2K for water-water cooling. SiC will beat those figures.<\/span><\/p>\nWhat does that mean in practice? For liquid duties, a glass exchanger often needs more area than a SiC unit to do the same job. But glass area is cheap, and a smooth glass surface holds its performance for years because deposits don\u2019t stick to it easily. When a supplier shows you a big heat transfer advantage for SiC, ask for the total installed cost for the same duty, not the coefficient alone. The same advice applies to any glass vs graphite heat exchanger comparison.<\/span><\/p>\n<\/span>What About a Titanium or Tantalum Shell and Tube Heat Exchanger?<\/b><\/span><\/h2>\nMetal still has a place in acid service. Titanium does very well with wet chlorine and oxidising chloride solutions. Tantalum is excellent with hot hydrochloric and sulphuric acids and handles pressure well.<\/span><\/p>\nThe catch is that each metal has a blind spot. Titanium fails badly in dry chlorine and some reducing acids, and tantalum is attacked by HF and hot alkali. Both are expensive, and their prices move with the metal markets. We\u2019d only look at a titanium shell and tube heat exchanger, or a tantalum one, when you need high pressure and a chemistry that rules out graphite and SiC. That\u2019s a smaller group of duties than most specs suggest.<\/span><\/p>\n<\/span>Which Material for Which Acid?<\/b><\/span><\/h2>\n\n\n\n| Process fluid<\/b><\/td>\n | Glass<\/b><\/td>\n | Graphite<\/b><\/td>\n | SiC<\/b><\/td>\n<\/tr>\n\n| Hydrochloric acid (hot, dilute)<\/span><\/td>\n | Excellent<\/span><\/td>\n | Excellent<\/span><\/td>\n | Excellent<\/span><\/td>\n<\/tr>\n\n| Sulphuric acid, all strengths<\/span><\/td>\n | Excellent<\/span><\/td>\n | Good at lower strengths and temperatures<\/span><\/td>\n | Excellent<\/span><\/td>\n<\/tr>\n\n| Nitric acid<\/span><\/td>\n | Excellent<\/span><\/td>\n | Poor when hot or concentrated<\/span><\/td>\n | Excellent<\/span><\/td>\n<\/tr>\n\n| Wet chlorine<\/span><\/td>\n | Excellent<\/span><\/td>\n | Limited<\/span><\/td>\n | Excellent<\/span><\/td>\n<\/tr>\n\n| Bromine<\/span><\/td>\n | Excellent<\/span><\/td>\n | Limited<\/span><\/td>\n | Excellent<\/span><\/td>\n<\/tr>\n\n| Hydrofluoric acid \/ fluorides<\/span><\/td>\n | Not suitable<\/span><\/td>\n | Good<\/span><\/td>\n | Good in directly sintered grades<\/span><\/td>\n<\/tr>\n\n| Hot concentrated phosphoric acid<\/span><\/td>\n | Not suitable<\/span><\/td>\n | Excellent<\/span><\/td>\n | Good<\/span><\/td>\n<\/tr>\n\n| Hot caustic soda<\/span><\/td>\n | Not suitable<\/span><\/td>\n | Limited, depends on impregnation<\/span><\/td>\n | Grade dependent<\/span><\/td>\n<\/tr>\n\n| Mixed organic solvents<\/span><\/td>\n | Excellent<\/span><\/td>\n | Good<\/span><\/td>\n | Excellent<\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/span>Tubes vs Shell: Do Both Need to Be Corrosion Resistant?<\/b><\/span><\/h2>\nOften, no. And this is where buyers save the most money.<\/span><\/p>\n | | | | | | | | | |