4″ NPS x 1290 PSI Stainless Steel Bridle

Design conditions and code edition

UG-22 loadings considered

UG-22 of Section VIII Division 1 requires the designer to consider every loading that can act on the vessel. For this bridle the following were evaluated and are recorded in the calculation file:

• Internal design pressure of 1,290 psi at 150 °F.
• Static head of test liquid during shop and field hydrotest (vertical orientation, water at 70 °F).
• Self-weight of the bridle and contents in the operating and test conditions.
• Wind: not applicable, the bridle is supported by mounting brackets to the parent vessel and is not free-standing.
• Seismic: no skirt, legs, or lug supports, so a seismic analysis was not required at the bridle level.
• Reactions from attached piping and instrumentation: covered by WRC 537 nozzle local-load checks at the 2 inch shell tap (see Accordion 4).
• Cyclic loading: not a fatigue-screened service.

Material toughness basis

The shell, pipe cap, straight flange, both nozzle necks, and the integrated tee are SA-312 TP304, SA-403 304, or SA-182 F304 austenitic stainless steel. All of these clear the impact-test exemption under UHA-51(d)(1)(a) because the carbon content does not exceed 0.10 percent, which gives a -320 °F rated MDMT for those components. The 1/2 inch threaded outlet on the head clears UHA-51(g) by stress-ratio at 0.2016, also rated to -320 °F. The B7 bolts on the Class 600 flanges are rated to -55 °F per Figure UCS-66 note (c). The reported -20 °F rated MDMT for the assembly is therefore limited by the design MDMT, not by any material on the unit.

Hydrostatic test basis

Shop hydrotest is the standard UG-99(b) case at 1.3 x MAWP corrected for stress ratio. The Shell 4 inch SCH 80S governs the stress ratio at 0.4804, but because the user-limited MAWP of 1,290 psi is well below the component MAWPs, the stress-ratio multiplier defaults to 1.0 and the test pressure is simply 1.3 x 1,290 = 1,677 psi at the gauge. A vertical field test at the same gauge pressure is also calculated and registered as an option. Test temperature of 70 °F clears UG-99(h) brittle-fracture floor by a wide margin because all pressure-retaining materials are exempt down to -320 °F.

Source: registered calculation package 004_1290_0000_+150_-20_V1 Rev. 0, pages 4 to 14.

Each pressure-retaining component was sized for the governing condition per the relevant ASME clause. The pipe-based components have substantially more pressure capacity than the user-set design pressure, so the assembly MAWP is limited to 1,290 psi by the Class 600 flanges. With zero corrosion allowance, UG-16(b) minimum wall of 1/16 in (0.0938 in) is satisfied by all components.

Pressure summary by component

The flanged connections (top flange, tee branch flange, and 2 inch shell flange) all rate at 1,318 to 1,320 psi at 150 °F under ASME B16.5. The user has chosen 1,290 psi as the design pressure to leave a small margin and to round to a typical class-rating-compatible spec. The pipe-and-cap components carry more than twice the design pressure in their wall calculation.

UG-16(b) governing minimum thickness

For pipe-based components with zero corrosion allowance, UG-16(b) requires a minimum wall of 1/16 in (0.0938 in). The shell, cap straight flange, and pipe cap all clear this floor on their pipe-tolerance-corrected wall (nominal x 0.875). The pressure equation governs design thickness on these components.

Hydrotest summary (vertical field test, gauge = 1,935 psi)

Local test pressure includes static liquid head at the component elevation. Allowable test stress = 0.9 S_y for stainless components per UG-99 commentary. Stress excessive flag is “No” for all components.

NI = not investigated (B16.5 flange components are checked by rating, not by test stress). Test gauge pressure at 70 °F = 1.3 x MAWP x LSR = 1.3 x 1,290 x 1 = 1,677 psi for shop test; vertical field test gauge of 1,935 psi shown above. Brittle-fracture provision UG-99(h) satisfied because all stainless components are exempt to -320 °F.

Material schedule

Nozzle schedule

All nozzle inside edges rounded per UG-76(c). All nozzle weld throats sized per UW-16 and verified by UG-41 weld failure path analysis. The 2 inch weldolet additionally checked for local-load capability against API 660 nozzle loads using WRC 537 (see Accordion 4).

Radiography summary

Marking includes the RT1 designator under UW-11(a)(5) because all Category A and B butt joints receive full radiography.

Dimensional summary

• Shell: 4.5 in OD x 0.337 in nominal wall x 44.5 in long.
• Pipe cap: 2.5 in overall length E, 1.2486 in straight flange L_sf.
• Top flange: NPS 4 Class 600 WN, 3.826 in bore.
• 2 inch weldolet projection: 1.3511 in available outside vessel; flange face at 4.4811 in projection.
• Empty weight: 197 lb. Operating weight: 222 lb. Test weight: 222 lb. Capacity 3 US gal. Surface area 10 ft².
• Liquid level reference: 57 in from datum.

The registered calculation file performs the following code checks. Each one is a discrete pass/fail item in the design record and is reproducible from the inputs in Section 1.

Pressure-retaining wall thickness

• UG-27(c)(1) circumferential stress for cylindrical shells. Shown as the Appendix 1-1 outside-diameter form for radii R_o greater than 0.5 R.
• Appendix 1-1 alternative thickness equations on the outside diameter basis. Used for the shell, the pipe-cap straight flange, and the cylindrical body of the B16.9 cap.
• Appendix 1-4(c) for the B16.9 pipe cap dish, with the K factor calculated from inside diameter and dish height.
• UG-32 formed-head requirements (referenced for the cap geometry check).
• UG-16(b) minimum wall thickness, 1/16 in plus corrosion allowance, applied to all pressure-retaining components. CA = 0 for stainless.
• UG-23 allowable stress lookup at design temperature for each material grade.
• UG-80(a) out-of-roundness tolerance check on the shell (1 percent of D).
• UG-81(a) out-of-roundness for the pipe-cap dish (1.25 percent outside / 0.625 percent inside).

Nozzle and opening reinforcement

• UG-37 area-replacement reinforcement check for N-H-01 (1/2 inch TOL on cap) and N-S-01 (2 inch weldolet on shell). Each nozzle reports A_required, A_available, A₁, A₂, A₃, A₅, A_welds.
• UG-40 limits of reinforcement parallel (L_R) and normal (L_H) to the vessel surface.
• UG-41 weld failure path analysis. The 2 inch weldolet is exempt from weld strength calculations per UW-15(b)(1) because the joint conforms to Fig. UW-16.1 sketch (a). The 1/2 inch TOL is also exempt under the same provision.
• UG-45 minimum nozzle neck thickness check for each connection.
• UG-76(c) requirement to round inside edges of openings.
• WRC 537 external-loads check on the 2 inch shell weldolet (N-S-01) using API 660 nozzle load envelope. Four load cases checked: operating, hot shut-down, P_r reversed, and P_r reversed at hot shut-down. Maximum combined stress 37,871 psi against an allowable of 60,000 psi; maximum local primary stress 19,950 psi against 30,000 psi. No overstress.

Welds and joint design

• UW-11(a) Type 1 full radiography on all Category A and B circumferential butt joints, qualifying the assembly for the RT1 marking.
• UW-15(b)(1) nozzle weld strength exemption for fillet welds conforming to Fig. UW-16.1 sketch (a).
• UW-16 weld sizing for nozzle attachment fillets. 1/2 inch TOL Leg₄₁ = 0.25 in (throat 0.175 in vs. 0.0656 in required); 2 inch weldolet Leg₄₁ = 0.375 in (throat 0.2625 in vs. 0.0938 in required).
• UCS-66.3(a) tapered-butt-weld transition checks where dissimilar wall thicknesses meet (referenced in the design record for any pipe-to-fitting wall mismatch).

Toughness and brittle fracture

• UHA-51(d)(1)(a) impact-test exemption for austenitic stainless steels with carbon content not exceeding 0.10 percent. Applies to the shell, pipe cap, straight flange, B16.9 tee, top flange, blind, branch flange, and the 2 inch weldolet shell flange. Rated MDMT for these components is -320 °F.
• UHA-51(g) stress-ratio path used for the 1/2 inch TOL: coincident ratio 0.2016, rated MDMT -320 °F.
• Figure UCS-66 note (c) for the SA-193 B7 bolts on the Class 600 flanges. Rated MDMT -55 °F.
• Assembly rated MDMT is reported as -20 °F because the user-specified design MDMT (-20 °F) is the warmer of the design and component limits, and the rated MDMT cannot be colder than the design MDMT.

Hydrostatic test

• UG-99(b) shop hydrostatic test at 1.3 x MAWP. Lowest stress ratio across components is 0.4804 (Shell 4 inch SCH 80S), but because the user-limited MAWP is well below the component MAWPs, the LSR multiplier defaults to 1.0 in the test-pressure calculation.
• UG-99(h) brittle-fracture provision: shop test at 70 °F is well above the -320 °F floor for all stainless components.
• Vertical field test option calculated at the same gauge pressure (1,935 psi local) for in-service retest, all components clear with stress less than allowable.

Marking and registration

• UG-116 nameplate marking content. RT1 designator applied because all Category A and B joints are full radiography.
• Canadian Registration: CRN AA3841.2, jurisdiction Alberta. Calculation file 25-050.

The four examples below are pulled from the registered calculation package and show the actual numbers used to register CRN AA3841.2. Each one shows the input, the equation, the substitution, and the result.

Example 1. Shell wall thickness and MAWP, Appendix 1-1

NPS 4 Sch 80S (XS) SA-312 TP304 welded and seamless pipe, 4.5 in OD, 0.337 in nominal wall, pipe tolerance factor 0.875, 1.00 joint efficiency, 0 corrosion allowance.

Inputs: P + P_s = 1,291.76 psi (design plus 1.76 psi static head), R_o = 2.25 in, S = 20,000 psi (SA-312 TP304 at 150 °F), E = 1.00, c = 0.

Required thickness:

t = (P x Ro) / (S x E + 0.40 x P) + Corrosion
t = (1,291.76 x 2.25) / (20,000 x 1.00 + 0.40 x 1,291.76) + 0
t = 0.1417 in

UG-16(b) check: 1/16 + c = 0.0938 + 0 = 0.0938 in. Pressure equation governs.

MAWP at 150 °F (using nominal wall x mill tolerance 0.875):

P = (S x E x t) / (Ro - 0.40 x t) - Ps
P = (20,000 x 1.00 x (0.337 x 0.875)) / (2.25 - 0.40 x (0.337 x 0.875)) - 1.76
P = 2,764.36 psi

The shell carries about 2.14 times the user-set design pressure. UHA-51(d)(1)(a) stress ratio = (0.1417 x 1) / (0.2949 – 0) = 0.4804. Because TP304 carbon content does not exceed 0.10 percent, the shell is exempt from impact testing and the rated MDMT is -320 °F.

Example 2. B16.9 Bottom Pipe Cap, Appendix 1-4(c)

SA-403 304, NPS 4 SCH 80S B16.9 cap modified, dish height h = 0.9565 in, inside diameter D = 3.826 in, outside diameter D_o = 4.5 in.

Geometry factor K (corroded condition, c = 0):

K = (1/6) x [2 + (D / (2 x h))^2]
K = (1/6) x [2 + (3.826 / (2 x 0.9565))^2]
K = 1.0

Required thickness, corroded at 150 °F:

t = (P x Do x K) / (2 x S x E + 2 x P x (K - 0.1)) + Corrosion
t = (1,292.14 x 4.5 x 1) / (2 x 20,000 x 1 + 2 x 1,292.14 x (1 - 0.1)) + 0
t = 0.1374 in

MAWP, corroded at 150 °F:

P = (2 x S x E x t) / (K x Do - 2 x t x (K - 0.1)) - Ps
P = (2 x 20,000 x 1 x (0.875 x 0.337)) / (1 x 4.5 - 2 x (0.875 x 0.337) x (1 - 0.1)) - 2.14
P = 2,969.48 psi

The straight flange on the cap controls the cap MDMT, and clears UHA-51(d)(1)(a) at -320 °F.

Example 3. 2″ SCH 160 Weldolet on Shell, UG-37 area replacement

SA-182 F304 manufacturer-standard weldolet, 2.375 in OD, 0.344 in wall, 1.687 in inside diameter, 1.69 in long, set on the shell with a 0.375 in inner fillet (Leg₄₁). Local vessel minimum thickness = 0.2949 in.

Required nozzle wall (UG-27):

trn = (P x Rn) / (Sn x E - 0.6 x P)
trn = (1,291.7 x 0.8435) / (20,000 x 1 - 0.6 x 1,291.7)
trn = 0.0567 in

Required shell wall (Appendix 1-1):

tr = (P x Ro) / (S x E + 0.40 x P)
tr = (1,291.7 x 2.25) / (20,000 x 1 + 0.40 x 1,291.7)
tr = 0.1417 in

Limits of reinforcement (UG-40):

LR (parallel) = max [d, Rn + (tn - Cn) + (t - C)]
              = max [1.687, 0.8435 + 0.344 + 0.2949]
              = 1.687 in

LH (normal)   = min [2.5 x (t - C), 2.5 x (tn - Cn) + te]
              = min [2.5 x 0.2949, 2.5 x 0.344 + 0]
              = 0.7373 in

Area required (UG-37(c)):

A = d x tr x F + 2 x tn x tr x F x (1 - fr1)
A = 1.687 x 0.1417 x 1 + 2 x 0.344 x 0.1417 x 1 x (1 - 1)
A = 0.239 in^2

Area available:

A_available (0.8227 in²) is greater than A_required (0.239 in²), so the opening is adequately reinforced with a margin of 3.4x.

UG-45 minimum nozzle neck check:

ta (App 1-1)  = 0.0748 in
ta (UG-22)    = 0.1273 in
ta = max[ta(App 1-1), ta(UG-22)] = 0.1273 in
tb (App 1-1)  = 0.1417 in
tb1 = max[tb, tb_UG16] = 0.1417 in
tb  = min[tb3 (std wall - mill tol), tb1] = 0.1348 in
tUG-45 = max[ta, tb] = 0.1348 in
Available wall tn = 0.344 in. Passes with 2.55x margin.

UHA-51(d)(1)(a) toughness: stress ratio (0.1417 x 1) / (0.2949 – 0) = 0.4804, carbon content not exceeding 0.10 percent, so rated MDMT = -320 °F.

Example 4. 1/2″ Class 3000 TOL on Bottom Cap, UHA-51(g) stress-ratio path

SA-182 F304 threaded outlet boss on the bottom pipe cap, 0.84 in inside diameter, 0.14 in nominal wall, no corrosion allowance. Local vessel minimum thickness = 0.2949 in. Inner fillet Leg₄₁ = 0.25 in.

Required nozzle wall:

tr = (P x R) / (S x E - 0.6 x P)
tr = (1,292.17 x 0.42) / (20,000 x 1 - 0.6 x 1,292.17)
tr = 0.0282 in

UHA-51(g) stress ratio:

Stress ratio = (tr x E*) / (tn - c)
             = (0.0282 x 1) / (0.14 - 0)
             = 0.2016

The coincident ratio of 0.2016 is below the threshold for impact-test exemption under UHA-51(g), so the threaded outlet is exempt from impact testing at the design MDMT of -20 °F with a rated MDMT of -320 °F. Material is austenitic stainless and the carbon content does not exceed 0.10 percent, which is the parallel exemption under UHA-51(d)(1)(a).

Other components, summary

Source: registered calculation package 004_1290_0000_+150_-20_V1 Rev. 0, pages 14 to 46. Personal identifiers, license numbers, and seal images have been removed from the public version. The original sealed PDF is held in the Reece quality records.