TECTULby IMR

Fluid conveyance · Flange stud bolts and hardware

TECHNICAL DATA SHEET

FT-TC-BRI-ESP-001

Issue date: August 5, 2026 · Rev. 001

Check the current version

ASTM A193 B7 flange stud bolts with A194 2H nuts — quantity, diameter, length and calculated torque

TECTUL · Dispatch across Colombia · Exports to Central & South America

ASTM A193 grade B7 alloy steel stud bolts with ASTM A194 grade 2H nuts and washers, for carbon steel bolted flange joints. This sheet brings together on one page the three data sets that today live in separate and almost always incomplete documents: the master table of stud quantity, diameter and length by nominal size and flange class (150, 300 and 600, from 1/2″ to 12″); the certifiable properties of B7 and 2H; and a torque table calculated with T = K·F·d, declaring the thread stress area, the preload percentage of yield and the nut factor K for each lubrication condition. The spread between a MoS₂-lubricated thread and a dry thread is threefold: a torque figure without a declared lubricant means nothing.

SKU VT-86917 (carbon steel flange stud bolt) · stud kit with two 2H nuts and washers · 9 variants from 1/2″ × 2-1/2″ to 1″ × 6″, for 1/2″ to 10″ flanges · sold by the unit

1. Technical specifications and master bolting table

Master table: how many studs, of what diameter and what length

This is the table that settles the order. Quantity and diameter are set by the flange drilling in ASME B16.5 —they are not the buyer's choice— and the length is that of standard practice for raised face joints. The three columns cover the three classes in the TECTUL carbon steel flange catalog.

Lengths are tabulated in millimetres and the figure in brackets is their exact conversion at 25.4 mm per inch. They do not include the height of the stud points: a stud's length is measured end to end of the threaded body, without the end cones or chamfers, and this is the most common cause of an order coming up short. Nor do they allow for washers: each washer adds its thickness to the length required. The dimensions, bolt circle and hole diameter of each flange are in data sheets FT-TC-BRI-AC-001 (carbon steel) and FT-TC-BRI-INOX-001 (stainless).

The catalog's 9 stud variants, checked against the standard

The TECTUL catalog publishes the stud as a kit: the stud with its two 2H nuts and galvanized washers, referenced by diameter × length and by the flange size it serves. Checking it against the table above is useful because it explains the differences:

Two readings from this comparison. First: from 1/2″ to 8″ the catalog stud diameter matches exactly what ASME B16.5 assigns to Class 150, and its lengths run between 0 and 13 mm above the tabulated length — a margin consistent with the washers the kit includes, which are not part of the standard length. Second: the 1″ × 6″ variant for a 10″ flange does not correspond to Class 150, whose 10″ stud is 7/8″, but to the Class 300 diameter (1″). The catalog does not declare each variant's class: before ordering you must check against the flange's actual drilling, because a 1″ stud does not fit the 1″ hole of a 10″ Class 150 flange.

Materials: A193 B7 for the stud, A194 2H for the nut

This is the standard pair for carbon steel bolted flange joints, and they are not interchangeable with structural or hardware-store bolting. B7 is a chromium-molybdenum steel (AISI 4140/4142/4145 type), quenched and tempered: its strength comes from the heat treatment, not from the alloy alone. 2H is a heavy hex nut in medium carbon steel, also quenched and tempered at no less than 455 °C (850 °F), sized so it does not yield before the stud does.

The property step by diameter matters when calculating torque: above 2-1/2″ the B7 loses strength (from 125 to 115 ksi tensile and from 105 to 95 ksi yield) because the quench does not penetrate a larger section equally. Every diameter in this catalog (1/2″ to 1-1/4″) sits in the first range, the 105 ksi yield one, which is the value used to calculate the section 2 table.

Marking: what you verify at goods-in without testing anything

General specifications

2. Engineering calculation: tightening torque, T = K·F·d

Why a torque table with no declared lubricant is useless

A stud's tightening torque is not a property of the stud: it is the moment you must apply to obtain a tensile force, and the relation between the two is governed by friction. The equation in ordinary use is T = K · F · d, and the troublesome term is K, the nut factor: an empirical number summarizing friction on the thread flanks and on the nut bearing face. That number ranges from 0.13 to 0.40 depending on the state of the thread, and with it the torque changes at equal preload. That is why a torque table declaring neither the percentage of yield nor K cannot be audited: you cannot tell whether it over- or under-tightens.

Where T is torque (lb·ft or N·m), K the nut factor (dimensionless), F the target preload (lbf or kN) and d the stud nominal diameter (inches or metres). The preload comes from the thread stress area and the target stress: F = As · S.

The three parameters this sheet declares before calculating

Calculated tightening torque table — 50 % of B7 yield

This table is calculated with the equation and the three parameters declared above, not copied from a tool catalog: anyone can reproduce it. It covers precisely the 1/2″ to 1″ diameters that hydraulic wrench makers leave blank because their tooling starts higher up, and which are the ones fitted to the 1/2″ to 12″ flanges in the catalog. Torques are rounded to the unit. The final torque is governed by the gasket: if its manufacturer specifies a seating stress or a crush limit, that figure prevails over this table.

Tightening sequence: star pattern, in passes, plus a circular closing pass

Reaching the calculated torque is not enough: you must get there in a way that leaves the gasket uniformly compressed. The ASME PCC-1 procedure for a ring-gasket bolted joint reads as follows:

1. Pre-checks: faces clean and undamaged, flanges aligned and parallel before inserting bolting, studs and nuts clean and lubricated with the lubricant declared in the torque figure.
2. Initial hand snugging to contact, checking that the gasket is centred.
3. Pass 1 in star pattern, to 20–30 % of target torque.
4. Pass 2 in star pattern, to 50–70 % of target torque.
5. Pass 3 in star pattern, to 100 % of target torque.
6. Pass 4 circular, at 100 %, following the studs in order around the flange, until no nut turns any further. This pass is what recovers the loss of tightening caused by gasket bedding-in and stud-to-stud interaction: without it the joint ends up unevenly preloaded even though every stud has seen its torque.

A "star" sequence means tightening diametrically opposite studs alternately, not consecutive ones. The logic is the same as fitting a wheel: tightening in order around the circle lifts the gasket on one side and crushes it on the other. On large flanges or critical service, torque control is replaced by stud elongation control (hydraulic tensioner or ultrasonic measurement), which removes the K uncertainty entirely — at the cost of specialized equipment.

3. How it is measured, how it is ordered and when B7 will not do

How a stud is measured (and why they arrive short)

A stud's length is measured end to end of the body, without the points —the cones or chamfers that help the nut start—. Tabulated lengths for bolted joints refer to that measurement. The three mistakes that make a stud ordered "per the table" come up short:

Thread protrusion: how much must stick out

After tightening, the stud thread must protrude past the outer face of each nut far enough for every thread in the nut to be engaged. The field rule is that the stud end finishes flush with the nut face or above it; a stud ending inside the nut leaves threads unloaded and reduces the joint's capacity with nothing visible from outside. It is a visual check made during the final tightening pass and it costs nothing.

Why flanges use a through stud with two nuts rather than a bolt

A machine bolt has a head and partial threading: preload transfers through the head bearing surface and the thread works at one end only. A stud bolt is threaded along its whole length and takes two nuts, one per face. That gives it three advantages in a bolted flange joint:

• Load symmetry: force enters equally from both ends, without the eccentricity a hex head introduces.
• It can be tightened from either side, which on an assembly against equipment or a wall can be the difference between being able to do it and not.
• Disassembly: if one nut seizes through corrosion, you attack the other; with a bolt whose head has seized there is no second option but to cut it.

Coating: it changes the torque, not the material

Coating changes neither the steel grade nor its mechanical properties: it changes friction, and with it the torque needed for the same preload. That is exactly the K term in section 2. Change the finish without recalculating the torque and the real tightening changes even though the wrench reads the same number. The kit's galvanized washers also do a mechanical job: they spread the nut load and protect the flange face as the nut turns.

When B7 is not the right bolting: B8 and B8M

B7 is chromium-molybdenum steel: strong and economical, but not stainless. In three situations austenitic ASTM A193 grade B8 (type 304) or B8M (type 316) bolting with A194 grade 8 or 8M nuts is specified:

• Stainless steel flange and line (data sheet FT-TC-BRI-INOX-001): a carbon steel stud in contact with a stainless flange in the presence of moisture forms a galvanic couple in which the stud is the anode and corrodes preferentially. It is a case where the cheap part eats itself to protect the face.
• Corrosive or marine environments, where zinc-plated B7 loses its layer and starts pitting, even with a carbon steel flange.
• Cryogenic or high-temperature service outside B7's practical range, where the austenitic grade's toughness or relaxation resistance is required.

The trade-off is that B8 and B8M have lower mechanical strength than B7 in the usual supply condition, so the target preload —and therefore the torque— is different: you cannot use the section 2 table, which is calculated on B7 yield. When the project additionally requires electrically isolating the bolted joint to prevent galvanic corrosion in the line itself, the answer is not the stud material but a complete isolation kit (sleeve, insulating washers and gasket), which is a different product.

4. Frequently asked questions

How many studs does a 4″ flange take, and of what diameter?

8 studs of 5/8″ in Class 150, 90 mm long for a raised face joint. In Class 300 it is 8 of 3/4″ at 115 mm and in Class 600, 8 of 7/8″ at 145 mm. Quantity and diameter are not the buyer's choice: they are set by the flange drilling in ASME B16.5. The full table from 1/2″ to 12″ in all three classes is in section 1.

What is the tightening torque of a 1/2″ stud on a Class 150 flange?

It depends on the lubricant, and that is the important answer. For a preload of 50 % of A193 B7 yield: 40 lb·ft (55 N·m) with a MoS₂-lubricated thread (K = 0.13), 62 lb·ft (84 N·m) with machine oil (K = 0.20) and 124 lb·ft (168 N·m) with a dry or rusted thread (K = 0.40). All three torques produce the same tightening; what changes is the friction to be overcome. And above all that the gasket governs: if its manufacturer gives a seating stress, that figure prevails.

Why do the torque tables I find give such different values?

Because almost none of them declares its two assumptions. A torque figure only means something if it states what percentage of yield the stud is being preloaded to (the 50 % in this sheet, or the 70 % hydraulic tooling tables use) and with what nut factor K. Between K = 0.13 and K = 0.40 there is a threefold ratio, and between 50 % and 70 % of yield another 40 % of difference. Two "correct" tables can differ by more than fourfold without either being wrong.

Can a joint be tightened without lubricating the thread?

It can, but you must tighten to the dry-thread torque —up to three times the lubricated one— and accept much greater scatter between studs, because the friction of a dry or rusted thread is the least repeatable thing in the whole assembly. In practice it is not worth it: lubricant is cheap, it reduces the torque required, it makes the tightening repeatable and it prevents the corrosion seizing that turns a future disassembly into grinder work. What you must never do is lubricate and apply the dry table torque, or the reverse.

What is the difference between a B7 stud and a hardware-store bolt of the same diameter?

The steel grade and its heat treatment. ASTM A193 B7 is a quenched and tempered chromium-molybdenum steel with 860 MPa (125 ksi) minimum tensile and 725 MPa (105 ksi) minimum yield, marked "B7" on the end. An ordinary carbon steel bolt can have less than half that strength with the same thread and the same appearance. In a bolted flange joint that means that at table torque the bolt passes its yield point and the joint loses tightening within the first hours of service.

Can I use ordinary nuts instead of 2H?

Not in a bolted flange joint. ASTM A194 grade 2H is a heavy hex nut (taller and wider than the standard one) in quenched and tempered medium carbon steel, with a 175 ksi minimum proof load: it is sized so the stud reaches its preload without the nut yielding first. A lower grade nut deforms at the thread and releases tightening progressively. It is identified by the "2H" mark plus the manufacturer's identification on one face.

Is a galvanized stud tightened to the same torque as a black one?

No. Coating does not change the steel grade, but it does change friction, and friction is the K term in the torque equation. Hot-dip galvanizing has a thick layer and different friction behaviour from oxidized black or electroplated zinc, besides requiring an oversize-tapped nut. If the finish changes, recalculate the torque with the corresponding K; if the K of the supplied finish is unknown, request it from the supplier or move to elongation control.

When must B8 or B8M stainless studs be used?

When the flange is stainless steel, when the environment is corrosive or marine, or when service falls outside B7's practical range. The most frequent case is the first: a carbon steel stud bolting a stainless flange in the presence of moisture forms a galvanic couple in which the stud is the anode and corrodes to protect the flange. Watch the torque: B8 and B8M are mechanically weaker than B7 and the section 2 table does not apply.

5. Application notes

6. Technical notice and limitation of liability