Why "Heat Efficiency Tubes" Is a Different Conversation at −196 °C

Above 0 °C, the question "which heat efficiency tubes do I buy" is a question of geometry: fin profile, pitch, fin height, base-tube material. Below 0 °C — and especially below −46 °C where the line class flips to low-temperature piping — the same question becomes a question of fracture toughness, impact energy, post-bend heat treatment, and the heat-to-heat traceability of the base tube.

A spiral-wound LNG heat exchanger, an open-rack ambient-air LNG vaporizer, a primary reformer waste-heat boiler, an ethylene cold box, an air-separation unit (ASU) main heat exchanger, and an ammonia cold box all rely on heat efficiency tubes — but each one imposes a different envelope on the base tube, the fin, the bend, the weld, and the inspection regime. This guide maps the envelope and the procurement logic for each.

The Five Cryogenic Duty Families a Buyer Must Distinguish

"Cryogenic" is a spectrum. A buyer who treats it as one family ends up over-specifying aluminum where 304L works, or under-specifying 9% Ni where austenitic stainless embrittles. The five duty families are defined by minimum design metal temperature (MDMT) and the fluid on the tube side.

Once the duty family is fixed, the rest of the heat efficiency tubes decision — fin process, base-tube spec, U-bend heat treatment, MTC level — follows from the table above and the cross-reference tables in the next section.

Base Tube Materials — The Underlying Procurement Decision

A fin is only as good as the tube it is bonded to. For cryogenic service, the base tube is the load-bearing member, and the fin is a heat-transfer amplifier. Five base-tube families cover 95 % of cryogenic heat efficiency tubes orders.

1. Austenitic stainless 304L / 316L — the workhorses down to −196 °C

304L (UNS S30403, ≤0.030 % C) and 316L (UNS S31603, ≤0.030 % C with 2-3 % Mo) are the default cryogenic tube materials. They retain full austenitic toughness down to the boiling point of LNG (−162 °C) and to the boiling point of liquid nitrogen (−196 °C), provided the carbon is held low to avoid chromium-carbide sensitization at the HAZ of any future weld repair. Standards: ASTM A213 / A249 / A269 / A312 (tube and pipe), EN 10216-5, JIS G3463, GOST 9941, GB/T 14976 and GB/T 13296 for the boiler / exchanger side. Charpy V-notch at −196 °C is typically ≥ 60 J full-size on the base tube (per ASME BPVC Section VIII and EN 13480-4). 316L adds 2-3 % Mo for chloride-bearing duty (AAV humidity, FSRU regasification, coastal ASU).

2. 9 % Ni steel — the historical LNG storage coil at −196 °C

9 % Ni (ASTM A333 Gr.8, ASTM A353, EN 10028-4 X7Ni9 / X8Ni9, JIS G3460 STPL690) is the heritage choice for large LNG storage tank inner tanks, primary LNG carriers, and cryogenic pipework for tanks larger than about 4,000 m³. It maintains ≥ 34 J Charpy at −196 °C in the Q&T condition. 9 % Ni is a low-carbon martensitic-austenitic matrix with retained austenite; the high alloy content makes it expensive (typically 4-6× the price of 304L per unit length) and limits mill availability. For a tube-bundle heat efficiency tubes order that does not require 9 % Ni, 304L is the lower-cost option.

3. Low-temperature carbon — A333 Gr.6 / A671 / A672 for utility cold duty

ASTM A333 Gr.6 (carbon steel, normalized, fine-grain, impact tested) is the correct choice for propane / propylene / ammonia service between −29 °C and −46 °C. Equivalent standards: EN 10216-4 (P265NL for −40 °C, 11MnNi5-3 for −60 °C), JIS G3460 STPL380 / STPL450, GOST 8734 / 8736, GB/T 18984 (16MnDG, 09MnNiD for −40 °C and −70 °C). A333 Gr.6 is widely stocked and costs roughly 1.5-2.5× an A106 Gr.B at the same schedule, but avoids the step up to austenitic. The matching pipe fitting / flange is A350 LF2 (Class 1) for flanges and butt-weld fittings; A420 WPL6 for fittings to A333 Gr.6 pipe.

4. Copper-nickel 90/10 and 70/30 — for the seawater side of an LNG regasification terminal

90/10 (UNS C70600, CuNi10Fe1Mn) and 70/30 (UNS C71500, CuNi30Fe1Mn) are the standard materials for the seawater-side piping of open-rack LNG vaporizers and FSRU regasification skids, where the warmed seawater (typically +5 °C to +25 °C) gives up its heat to the LNG inside the finned tube. Standards: ASTM B466 / B467 (seamless / welded), EN 12451 / 12452, EEMUA 144 / 234, GB/T 8890, JIS H3300. 90/10 supports 2.5 m/s continuous / 4.0 m/s peak; 70/30 supports 3.5 m/s continuous. For LNG-vaporizer service the warm side is at +5 °C to +25 °C, so the alloy is in its comfort zone. The 4-8× seawater-corrosion advantage over carbon steel is the reason copper nickel alloy dominates this duty.

5. Aluminum 1060 / 3003 / 5083 — for plate-fin and ambient vaporizer fins

Aluminum is the dominant fin and base-tube material for the PFHE (plate-fin heat exchanger) core of large LNG, ethylene and ASU mixed-refrigerant cold boxes. 3003 (AlMnCu) and 5083 (AlMg4.5Mn) are the workhorse brazing-sheet alloys for vacuum-brazed PFHE cores; 1060 and 3003 are the workhorse fin and tube alloys for open-rack AAVs. The AA-AA composite (aluminum tube with aluminum fin) avoids the galvanic-couple problem of copper-fin-on-steel-tube or steel-fin-on-copper-tube in humid or marine atmospheres. Cryogenic Charpy at −196 °C is not the limiting factor for aluminum (aluminum does not undergo a ductile-brittle transition like ferritic steel); the limiting factor is weld-procedure qualification for the vacuum-braze cycle.

Fin Process Selection for Cryogenic and Cryogenic-Adjacent Service

A fin is a heat-transfer amplifier. The job of the heat efficiency tubes fin is to add external surface area on the air side (or the gas side, in a PFHE) without corroding, without losing bond over time, and without creating a thermal short. Six process families dominate; only three belong in cryogenic duty.

Extruded aluminum fin (for PFHE cores and AAVs)

The fin is a continuous aluminum sleeve extruded over the aluminum tube, then shaved to final OD. The bond is a metallurgical diffusion bond — the fin becomes part of the tube wall. This is the standard construction for plate-fin PFHE cores (LNG SMR, AP-N, AP-X, mixed-refrigerant cold box) and for open-rack AAV tubes. Process reference: ISO 9303 (vocabulary), JB/T 10326 (tolerances), GB/T 14976 and GB/T 8163 (base tube). Bond strength is not measured as "pull-off" the way HFW fins are; it is implicit in the absence of debond after the vacuum-braze cycle (~600 °C, vacuum, 30-90 min).

HFW (high-frequency welded) helical fin — for ambient-vaporizer service in humid atmosphere

A steel or stainless strip is helically wrapped around the tube and continuously welded along both edges with an HFW (high-frequency induction) process. Bond is metallurgical, typically pull-off ≥ 150 N/cm per JB/T 10326. HFW is the right process for humid coastal AAVs and for air-cooled fin-fan heat exchangers, but the HFW heat-affected zone on a 9% Ni base tube is a problem at −196 °C and is generally not used in pure cryogenic service. The more common configuration is HFW fin on a 304L base, used on the warm side of the cold box where the base temperature is between −20 °C and +50 °C.

G-fin (embedded) and L-foot (wrapped) — for moderate cryogenic-adjacent service

G-fin (a rectangular fin foot embedded in a longitudinal groove skived into the tube) and L-foot (a fin foot wrapped over the tube and spot-welded) are lower-cost than HFW and survive the thermal cycle of start-up and shutdown. They are common on the cool side of the cold box (around −50 °C to −80 °C), on the methane-compressor interstage coolers, and on the mixed-refrigerant compressor aftercoolers. They are not used on the base tube of an LNG process stream directly at −162 °C; that base tube is unfinned 304L or 9 % Ni and the cryogenic duty is handled by a U-bend or a coil.

U-Bend Tubes — Why Cryogenic U-Bend Needs Post-Bend Heat Treatment

A U-bend tube is the standard geometry for the tube bundle of a shell-and-tube kettle reboiler, a feedwater heater, and a cryogenic cold-box coil. The bend process work-hardens the extrados and leaves residual stresses that, at cryogenic temperature, can initiate a brittle fracture. The remedy is post-bend heat treatment, and the rules are well documented in the standards.

Cold bending + solution anneal for austenitic stainless (304L / 316L / 321 / 347)

Cold bending of an austenitic 304L or 316L tube increases the hardness at the extrados from a typical 180-200 HV base to 240-280 HV at the apex. At −196 °C, the bend apex is still ductile (austenitic stainless does not have a ductile-brittle transition), but the work-hardened region has higher yield and lower uniform elongation, and it is the preferential site for stress-corrosion cracking in chloride-bearing service. ASTM A688 (welded austenitic U-bend tube for feedwater heater) and EN 10216-5 Annex B require solution anneal at 1,040-1,100 °C followed by water quench for austenitic U-bends in cryogenic service. The solution anneal restores the 180-200 HV base hardness and dissolves any chromium-carbide sensitization from the welding of longitudinal seam. The result is a bend apex with full cryogenic Charpy (≥ 60 J at −196 °C full-size).

Induction bending for 9 % Ni and large-diameter stainless

Induction bending uses localized heating (typically 900-950 °C for 9 % Ni, 1,050-1,100 °C for stainless) and a water-quench trailing shoe to bend the tube. It produces a thinner, more uniform bend than furnace or sand-pack bending, and the wall-thinning at the extrados is typically 4-6 % (vs 6-9 % for cold bending and 8-10 % for sand-pack). For 9 % Ni U-bend coils on LNG storage tank inner tank piping, induction bending is the standard because the wall-thinning stays within the −12.5 % tolerance of A333 Gr.8 and the as-bent hardness stays in the 200-230 HV range without a separate solution anneal.

Bend radius, ovality, and wall thinning — what EN 13480 and TEMA allow

EN 10216-5 Annex B (for seamless austenitic) and TEMA RCB-4.32 (for shell-and-tube) cap the bend ovality at 8-10 % and the wall-thinning at the extrados at 10 % (12.5 % for some low-alloy standards). The minimum bend radius (CLR, center-line radius) is 1.5 × OD for the typical U-bend, 1.25 × OD for hairpin designs, and 3 × OD for the bends that go over a tubesheet. Cryogenic U-bend tubes almost never go below 1.5 × OD; the extra bend radius costs metal but the cold work stays manageable.

Standards, MTC, and NDT — The Cryogenic Paper Trail

Cryogenic buyers do not buy tubes by the inch. They buy bundles of tubes that arrive on a single mill, with a single mill test certificate per heat, and the entire bundle can be cross-referenced to the same heat for traceability. Five standards and three certificate types drive the conversation.

The standards the cryogenic buyer quotes on the RFQ

• ISO 9303 — vocabulary and tolerance framework for finned tubes. The international umbrella. Use it as a reference even when the project is American.
• JB/T 10326 — finned-tube technical conditions (pitch ±0.5 mm, fin-height ±0.2 mm, welded-fin pull-off ≥ 150 N/cm, base-tube wall-tolerance ±10 %). The most cited domestic standard on fin-tube tolerances.
• EN 10216-5 — seamless austenitic stainless steel tubes for pressure and cryogenic service. The EN equivalent of ASTM A213 / A312. Most Asian and European cryogenic RFQs cite EN 10216-5 over ASTM.
• EN 10216-4 — seamless low-alloy and alloy steel tubes for pressure and low-temperature service. EN counterpart of A333 / A334. Covers 11MnNi5-3 (down to −60 °C) and 13MnNi6-3 (down to −80 °C).
• EEMUA 145 — specification for 90/10 and 70/30 Cu-Ni tubes for offshore and marine service. The reference that ties Cu-Ni tube procurement to seawater-side envelope.
• ASME B31.3 Chapter IX — high-pressure piping for cryogenic service. The code that ties the base tube, the bend, the weld, and the NDT together. Cryogenic heat efficiency tubes almost always end up inside an ASME B31.3 Chapter IX piping system.
• EN 13480-4 — metallic industrial piping, fabrication and installation. EN counterpart of ASME B31.3. Cryogenic U-bend heat treatment is documented here.

MTC type — 3.1 vs 3.2, and why 3.2 is the cryogenic default

EN 10204 defines four MTC types: 2.1 (compliance statement), 2.2 (test report), 3.1 (mill-issued with independent inspection), 3.2 (mill-issued with independent third-party inspection). Cryogenic buyers default to 3.1 as the floor and 3.2 for any tube destined for LNG, ethylene, ammonia cold-box, or main cryogenic heat exchanger service. The premium for 3.2 over 3.1 is typically 1.0-1.5 % of the tube value plus a 5-10 working-day delay; on a 100 t LNG bundle the 3.2 premium is in the USD 8,000-15,000 range and the delay is often the controlling factor. A buyer who orders 3.1 and is told at the pre-shipment meeting that 3.2 is required is going to lose two to three weeks in the schedule.

NDT regime — 100 % ECT, 100 % PMI, and selective UT

For 304L and 316L stainless steel pipe destined for cryogenic U-bend service, the standard NDT regime is 100 % eddy-current testing (ECT) per ASTM E243, 100 % positive-material identification (PMI) per ASTM E1476 with XRF on the upstream end of each tube, hydrostatic test at 1.5 × design pressure for 10-30 s per ASTM A1015 or EN 10216-5 §10, and selective ultrasonic testing (UT) on the welded seam of any welded tube per ASTM A388 / E213. For 9 % Ni, the ECT calibration is harder (high nickel and ferrite distort the eddy-current response); most specs call for 100 % magnetic-particle inspection (MT) on the seam and 100 % PMI, with hydrostatic at 1.5 × design.

Five Sourcing Traps Specific to Cryogenic Heat Efficiency Tubes

These five traps are the ones that bite a cryogenic heat efficiency tubes procurement in 2026. Each has cost the industry a quarter or two of project delay at some point in the last decade.

Trap 1 — Specifying 9 % Ni where 304L works

A buyer who defaults to 9 % Ni "because it's cryogenic" pays 4-6× the price of 304L for the same Charpy at −196 °C. 9 % Ni is the right choice for the LNG storage tank inner tank and for primary structural piping above 4,000 m³ capacity. For the tube bundle of a spiral-wound LNG, an ethylene cold box, an ASU main exchanger, or a methane compressor intercooler, 304L is fully qualified at the same −196 °C Charpy. The procurement litmus test: if the base tube is going through a U-bend or a brazed fin, and the design temperature is above −162 °C, 304L is the answer.

Trap 2 — Ordering 3.1 when the spec calls for 3.2

A buyer's internal standard calls for EN 10204 3.2 MTC, but the RFQ is typed as "MTC 3.1/3.2 acceptable". The mill produces 3.1 because it is faster and cheaper. The third-party inspector flags the 3.1 at the pre-shipment meeting. The bundle sits at the mill for two to three weeks while the third-party inspection is arranged. The fix: type 3.2 on the RFQ and add a 5-10 working-day buffer to the schedule up front, or accept 3.1 in writing only if the spec truly allows it.

Trap 3 — Skipping the post-bend solution anneal on 304L U-bend

Cold-bent 304L U-bend without a post-bend solution anneal will pass the room-temperature hydrostatic and the room-temperature Charpy. At −196 °C, the work-hardened extrados has lower uniform elongation and is the preferred site for chloride SCC in any service that includes moisture. A mill that quotes "U-bend in 304L, cold-formed only" without an explicit solution anneal should be challenged. The fix: write "post-bend solution anneal at 1,050-1,100 °C, water quench, hardness ≤ 200 HV at the bend apex" into the RFQ.

Trap 4 — Buying the fin and the base tube from two different mills

A finned tube bundle with the base tube from mill A and the fin from mill B breaks the MTC chain. The bundle is now two half-traceable lots welded together, and any third-party inspector will flag it. The right move is one-mill single-MTC: the same heat, the same heat number, the same mill test certificate. Heat efficiency tubes are a bonded assembly, and the bonded assembly needs one paper trail.

Trap 5 — Not specifying Charpy at MDMT

A 304L tube from any reputable mill will pass room-temperature Charpy. The question is whether the heat has been impact-tested at the actual MDMT of the project. The fix: write "Charpy V-notch full-size, three specimens per heat per direction, at MDMT (typically −196 °C), acceptance ≥ 60 J average / 50 J minimum single specimen" into the RFQ. A 2.2 or 3.1 MTC that does not show the MDMT Charpy is a paper, not a cryogenic tube.

Mill-Direct Economics for Cryogenic Bundles

A 50-200 t cryogenic heat efficiency tubes bundle is the standard size for an LNG cold-box coil, an ethylene cold-box, a single-train ASU, or an AAV skid. At that volume, the mill-direct route saves 15-30 % per tonne over the regional stockist, and a bundled order that includes stainless steel pipe for the connecting piping, the pipe fittings for the B31.3 Chapter IX transitions, and the pipe flanges for the bundle-to-piping connection saves a further 8-15 % on total landed cost through consolidated logistics and one MTC chain.

Lead-time structure at the mill: 4-6 weeks for 304L base tube in standard OD/WT from mill stock, 6-10 weeks for the same tube in non-stock size or with the EN 10216-5 3.2 MTC, 10-14 weeks for 9 % Ni, 12-18 weeks for 254 SMO or other super-austenitic, and 16-22 weeks for a full cryogenic bundle that includes the U-bend, the post-bend solution anneal, the helical fin, and the final hydrostatic. A buyer who needs 4 weeks lead time is going to pay the stockist premium, not the mill-direct saving.

How EZ Steel Industrial Supplies Cryogenic Heat Efficiency Tubes

EZ STEEL Industrial (ezindustrialtube.com) has supplied heat efficiency tubes for boiler, air-cooled heat exchanger, refinery, and ethylene plant service for 30 years from a 480,000+ t/y capacity base. The cryogenic and cryogenic-adjacent scope is bundled under one mill, one MTC, and one quality plan.

The cryogenic-relevant product line

• U-bend tubes in 304L, 316L, 321, 347, 2205 / 2507, 9 % Ni — base tube to ASTM A213 / A249 / A312 / EN 10216-5 / JIS G3463 / GOST 9941; bend to ASTM A688 + EN 10216-5 Annex B + TEMA RCB-4.32; post-bend solution anneal at 1,050-1,100 °C with water quench on request.
• Finned tubes in L-foot, LL-foot, KL-foot, G-fin embedded, HFW helical welded, and extruded aluminum — base tube to ASTM A179 / A192 / A213 / A249 / A312, EN 10216-2 / -5, GB/T 8163 / GB/T 5310 / GB/T 14976 / GB/T 13296, JIS G3461 / G3463, GOST 8732 / 9940 / 9941.
• Stainless steel pipe (304 / 304L / 316L / 321 / 347) in ASTM A312 / A358 / A778 for the connecting piping of a cryogenic bundle.
• Copper-nickel tubes (90/10, 70/30) in ASTM B466 / B467 / B111 for the seawater side of an LNG vaporizer.
• Pressure tubes (A213 TP304 / TP316, A249, A269) for the warm side of the cold box and the interstage coolers.
• Carbon steel pipe (A106 / A333 / A671) for the warm utility side at −29 °C to −46 °C.
• Pipe fittings (B16.9 butt-weld, B16.11 socket-weld, B16.11 threaded, B16.3 malleable iron) in matching material and MTC.
• Pipe flanges (B16.5, B16.47, EN 1092-1) in A182 F304 / F316 / F51 / F53, plus A350 LF2 for low-temperature service.
• Industrial valves (gate, globe, check, ball, butterfly, cryogenic) in API 600 / API 6D / API 602 / API 594 with extended bonnet for cryogenic service.
• Gasket, stud bolt and nut in spiral-wound graphite, RTJ, A193 B7 / B7M / B8 / B8M, A194 2H / 2HM / 8 / 8M, A320 L7 / L43 for low-temperature.

The mill-direct and bundled-sourcing advantage

A 100 t cryogenic heat efficiency tubes order quoted by EZ STEEL arrives with the base tube, the U-bend, the post-bend heat treatment, the ECT, the PMI, the Charpy at MDMT, the 3.1 or 3.2 MTC, the matching pipe fittings in the same heat, the matching pipe flanges in the same heat, the industrial valves on the same purchase order, and the gasket, stud bolt and nut pack on the same heat-traceable paper trail. One supplier, one mill, one MTC chain, one shipment. The 8-15 % logistics saving of the bundled order and the 15-30 % mill-direct saving on the tube line together compound into a meaningful total-landed-cost reduction for the same cryogenic scope — a number that on a typical 100 t LNG or ethylene bundle lands in the high single-digit to mid-teen percent range, before the time saving from a single technical point of contact and a single MTC review.

9-Item RFQ Checklist for Cryogenic Heat Efficiency Tubes

An RFQ that is missing any of these nine items is going to come back with a quote that is either not comparable or that misses the cryogenic envelope.

1. Duty family — LNG / ethylene / ASU / ammonia / propane — and the MDMT in °C.
2. Base tube spec — UNS grade, ASTM / EN / JIS / GOST / GB standard, OD × WT × length.
3. Fin spec (if any) — fin process, FPI, fin height, material, bond-test method (pull-off for HFW, vacuum-braze cycle for extruded aluminum).
4. U-bend spec (if any) — CLR × OD, ovality tolerance, wall-thinning tolerance, post-bend heat treatment.
5. MTC level — EN 10204 3.1 or 3.2, plus which tests (Charpy at MDMT, ECT, PMI, hydrostatic, IGC) appear on the cert.
6. Charpy — full-size, three per heat per direction, at MDMT, acceptance ≥ 60 J average / 50 J min single (or per project spec).
7. Bundle scope — base tube + U-bend + fin + matching fittings + matching flanges + matching valves, or base tube only.
8. Quantity and lead time — tonnage, delivery date, EXW / FOB / CIF / DDP, port of discharge.
9. Heat-traceability — single-mill single-MTC, heat-number visible on each tube, certificates in the original language plus English.

Five FAQ Buyers Ask Before the Order

Q1. Is 9 % Ni still required for LNG storage tank inner tank piping, or is 304L acceptable?

For the inner tank of an LNG storage tank above about 4,000 m³ capacity and for the primary structural piping (the inner tank shell, the secondary barrier, the roof), 9 % Ni remains the code-of-practice and is referenced in EEMUA 147, EN 14620, and API 620 Annex Q. For the tube bundle of the LNG process stream (the main cryogenic heat exchanger, the methane compressor interstage coolers, the AAV fin tubes), 304L is fully qualified and is the lower-cost option. The procurement line: 9 % Ni for tank + structural; 304L for process bundle + AAV.

Q2. Can I use 316L instead of 304L for an LNG vaporizer in a coastal atmosphere?

Yes, and it is the better choice for chloride-bearing atmosphere. 316L adds 2-3 % Mo, which improves pitting resistance (PREN 24-26 vs 18 for 304L). In a coastal AAV the warm side carries seawater that splashes onto the bundle, and the chloride can attack 304L pitting sites. 316L is the standard for the warm-side tube of an ORAV; 304L is acceptable for the cold-side tube that stays below 0 °C and is dry. The cost adder of 316L over 304L is typically 15-25 % per unit length at the same schedule.

Q3. What is the practical minimum bend radius for a 304L U-bend at −162 °C?

The minimum CLR (center-line radius) for a 304L U-bend intended for cryogenic service is 1.5 × OD. Below 1.5 × OD, the wall thinning at the extrados rises above 10 % and the work-hardening at the apex becomes hard to anneal out. Hairpin (1.25 × OD) bends are used in plate-fin PFHE headers but not on a U-bend that goes around a tubesheet in a shell-and-tube bundle. The standard cryogenic U-bend is 1.5 × OD or 2 × OD, with 3 × OD reserved for the bends that go over a tubesheet.

Q4. Can a finned tube be a U-bend?

Yes, but the fin must be on the straight legs only, not on the bend apex. The bend apex is unfinned base tube, and the fin is wound or extruded only on the two straight runs. The transition from finned straight to unfinned bend is a defined point, typically 50-100 mm from the tangent of the bend, and the fin-edge is deburred to avoid cutting the bundle support. The post-bend solution anneal is performed on the whole tube, fin and all, with care taken not to melt the HFW fin bond.

Q5. How do I get a 4-week lead time on a 100 t cryogenic bundle?

You don't, from a mill. Mill-direct lead time for a 100 t cryogenic heat efficiency tubes bundle is 10-14 weeks for 304L in a non-stock size, 12-18 weeks for 316L or 9 % Ni, and 16-22 weeks for a full cryogenic bundle that includes the U-bend, the post-bend heat treatment, the helical fin, and the final hydrostatic. A 4-week delivery means buying from a regional stockist at a 20-40 % premium over mill-direct. The right move is to plan 14-18 weeks for a 100 t cryogenic bundle from the mill, and to keep a 2-4 week stockist safety stock for the emergency orders.