Control Valves for the Avatar Project: New 10 MW Steam Turbine, PT Muria Sumba Manis

When a working industrial plant adds a new 10 MW steam turbine, most of the attention goes to the turbine. What actually decides whether the new unit settles into steady operation, though, is the group of smaller machines around it — and the control valves are first among them. This page describes two forged-body globe control valves built for the Avatar project — a new 10 MW steam turbine at PT Muria Sumba Manis (MSM) in East Sumba, Indonesia: one 3-inch, one 2-inch, both Class 1500, both with pneumatic actuators and digital positioners.

1. The duty, in six lines

• Fluid: superheated steam, at pressure-reducing and distribution stations around the new turbine's steam system

• 3" valve: 30,000 kg/h, inlet 6.35 MPa(g) reduced to 4.0 MPa(g), 280.35 °C

• 2" valve: 10,000 kg/h, inlet 5.5 MPa(g) reduced to 4.0 MPa(g), 269.97 °C

• Rating: Class 1500, socket-weld ends per ASME B16.11

• Actuation: single-acting pneumatic, air-to-open, fail-close, with 4–20 mA + HART positioners

• Pressure testing (shell and seat) per BS EN 1349 / EN 12266-1; seat leakage class ANSI/FCI 70-2 Class IV (IEC 60534-4)

Everything else — the materials, the bonnet style, the trim decisions — follows from these six lines.

2. Where the valves sit, and why the numbers tell us

The duty figures are the story. Steam arrives at 6.35 and 5.5 MPa and is let down to a common 4.0 MPa header — the pressure level that feeds the turbine's auxiliaries and the process lines around it. At 280 °C the steam is comfortably superheated at both stations, which rules out erosion-by-wetness as a design driver and puts the emphasis elsewhere: tight shutoff, stable throttling across a wide load range (the two valves were sized for 10 and 30 t/h), and packing that survives continuous 280 °C service without hardening.

Both valves sit on continuously modulating duties, not isolation. That is why they are globe control valves with positioners rather than automated on-off valves — a distinction that matters when a plant specifies spares for a new turbine package.

3. The plant already runs pneumatic control valves — and we sized against them

MSM's existing steam system still operates older pneumatic control valves. The nameplates, documented by the plant: a Forbes Marshall Series 117-P1, DN80, ANSI 900, Kv 68 (seat Ø 62 mm), and a Series 113-L3, DN50, ANSI 900, Kv 12.10 (seat Ø 48 mm), both with diaphragm actuators on 4 bar instrument air.

These nameplates did two things for this order:

• They fixed the capacity target. The new 3-inch valve carries a rated Cv of 68 — the same value as the legacy DN80's Kv of 68, verified against the datasheet's own calculation (calculated Cv 44.61 at the normal duty, 64.9 % travel). The replacement matches the installed base rather than guessing upward.

• They confirmed the actuation philosophy. The plant has run pneumatic actuators on plant air for decades. The new valves keep that logic — single-acting spring-return actuators — while upgrading the intelligence from a mechanical positioner to a digital 4–20 mA + HART unit.

4. Two decisions made at drawing review

Two features of the final design differ from the first quotation round, and both are worth explaining because they are where a supplier either adds value or quietly de-scopes.

Single-stage trim. The first quotation carried a multi-stage balanced cage. At review, the numbers did not support it: the pressure ratio at the 3-inch station is 4.0/6.35 ≈ 0.63, in superheated steam — well within what a single-stage seat-and-cage passes while staying under the specified 85 dBA. A single-stage trim means fewer wearing parts, a simpler spare, and a lower price for the same Class IV shutoff and the same materials. Cutting stages here is not de-rating; it is sizing.

Socket-weld ends. Flanged ends were quoted first; the final design is SW per ASME B16.11. For welded steam piping at this size, socket welds remove the flange joint — the leak point most likely to weep steam within two years — and suit the plant's existing welded pipework.

What did not change between rounds: the forged F22 body, the Stellite-faced trim, the XM-19 stem, Class IV shutoff, and the HART positioner. The changes were execution details, not specification.

5. Configuration matrix

6. Why forged F22, a finned bonnet, and an XM-19 stem

Forged F22 body. F22 — 1.25Cr-0.5Mo steel — is the standard forged material for steam service in this temperature band, rated to 540 °C under ASME B16.34. Forging takes casting porosity off the risk list entirely: the body starts as a wrought billet with full-density grain structure, which matters at 1500 LB wall thicknesses where a casting defect found late costs weeks.

Radiation-fin bonnet. At 280 °C line temperature, the bonnet must keep the stem packing below the temperature where graphite oxidizes and stem lubricants degrade. The finned extended bonnet does that passively, with no purge or cooling water — the standard answer for continuously throttling steam valves.

XM-19 stem. The stem sees sliding contact under graphite packing, in steam, year after year. XM-19 (Nitronic 50, S20910) is a high-strength austenitic stainless with strong resistance to galling and corrosion — a better match for this duty than a standard 13Cr stem, and the reason the stem is listed by its UNS number on the datasheet rather than a generic grade.

7. Where this valve package is NOT the answer

• Liquid duties with high differential pressure. These valves were sized for superheated steam. A liquid letdown with choking and cavitation (a boiler feedwater letdown, for example) needs anti-cavitation trim selected against the actual liquid data — a different exercise.

• Duties where noise governs. The 85 dBA requirement is met by single-stage trim at these pressure ratios. At larger pressure ratios, a low-noise multi-stage cage is the correct hardware, and a single stage will not pass the prediction.

• Plants that need fail-open protection. Both valves here are fail-close. A letdown where closure would overpressure downstream equipment needs the opposite failure mode and a different spring arrangement.

• Hazardous-area instruments. This build is non-Ex (no certified positioner or solenoid). Locations classified for explosive atmospheres need certified accessories, which changes the actuator accessory list.

8. Verification and document package

Control valves are not acceptance-tested like on-off valves, and the test plan reflects that. The governing production-test standard for these valves is BS EN 1349, executed per its referenced valve-testing procedure EN 12266-1: shell strength verified by hydrostatic test at 39.0 MPa — the 1.5× proof against the Class 1500 F22 pressure rating (rated per ASME B16.34) at ambient temperature — followed by seat and packing tests. Seat leakage was verified against ANSI/FCI 70-2 Class IV (equivalently IEC 60534-4), the leakage classification the datasheet specifies, measured at the standard test conditions rather than a simple high-pressure hold. Around the pressure tests: mill test certificates for body, bonnet and trim materials, dimensional inspection against the approved drawing, and a functional stroke test of each actuator-and-positioner loop over 4–20 mA with HART communication verified. The plant receives a package it can file against the turbine project records, not just a crate.

9. FAQ

Why single-stage trim on a 1500 LB valve — isn't that under-engineered?

No. The stage count follows the pressure ratio and the noise prediction, not the pressure class. At a 0.63 ratio in superheated steam, a single stage meets Class IV shutoff and the 85 dBA limit; a multi-stage cage would add wearing parts and cost without changing what the valve does at these duties.

Why a forged body instead of a casting?

Forging removes casting porosity from the risk list and suits the 1500 LB wall section. F22 forged is the common forged grade for steam at this temperature, with ratings per ASME B16.34 to 540 °C.

Can these replace the existing control valves without touching the piping?

The socket-weld ends weld into standard B16.11 couplings, and the face-to-face was confirmed at drawing stage before production. What must be checked case by case is the piping schedule at the weld prep and the actuator headroom above the line.

What does the HART positioner actually add over a pneumatic one?

Beyond the 4–20 mA control signal, HART gives the plant digital access to travel, deviation and loop diagnostics from the DCS or a handheld — useful on continuously modulating valves, where a drifting positioner shows up as a slow process problem before anyone looks at the valve.

10. Send us these eight lines and we will quote

• Fluid and state (steam / water / gas)

• Flow rate: maximum, normal, minimum

• Inlet and outlet pressure at each flow condition

• Temperature

• Pipe size and schedule; end connection required

• Shutoff class and failure mode

• Instrument signal (4–20 mA? HART?) and air supply available

• Any standards the package must comply with

Valve technical data on this page: Flowks specification sheets and shop drawing for model FKM1062-1500Lb(I), 2" and 3", July 2025.