Raychem STS-MT/21.50 Skin-Effect Tracing Wire for Pipelines

STS-MT/21.50 is the 21 mm2 (#4 AWG) conductor version of the Raychem STS-MT tracing wire, the insulated conductor used in an STS skin-effect trace heating system for long pipelines. The datasheet lists part number F93310-000, a 5,000 Vac rating and maximum operating temperature of 150 C.

Long-pipeline heat tracing with one power point every few kilometres

In an STS system the insulated wire is pulled into a heat tube that is welded or strapped to the carrier pipe, and the system heats the pipe by the skin effect. The datasheet says STS systems minimise the number of connection and power-source locations, with circuit lengths up to 25 km (15 miles) possible, and are suited to embedded or long pipeline applications.

The wire is a tinned-copper conductor with chemical-resistant insulation and an enhanced polyolefin outer jacket, and meets IEEE 844.1 / CSA C22.2 No. 293.1 and IEEE 844.2 / CSA 293.2 at 5,000 Vac, as stated by the maker. It is approved in hazardous and non-hazardous locations only when used within a Chemelex-designed STS system.

Features stated in the datasheet

• Voltage rating 5,000 Vac maximum; maximum operating temperature 150 C (302 F); power output up to 150 W/m (45.7 W/ft).
• Traced surface type metal and concrete; resistant to organic and aqueous inorganic chemicals and corrosives.
• Three conductor sizes: 33.50, 21.50 and 13.50 (mm2 designation).
• ATEX and IECEx certificates for gas and dust atmospheres (the installation manual prints T6 to T3 for STS-MT, the datasheet T6 to T2 for ATEX, so confirm the temperature class in the project documents).

Technical specification

Specification of STS-MT/21.50

Choosing the conductor size

Three sizes are listed: STS-MT/33.50 A42886-000 (33 mm2, 14.0 mm OD, 433 kg/km), STS-MT/21.50 F93310-000 (21 mm2, 12.7 mm OD, 300 kg/km) and STS-MT/13.50 F74409-000 (13 mm2, 11.4 mm OD, 200 kg/km). The conductor size is set by the system electrical design, not chosen alone.

The datasheet is firm that STS systems are custom-designed and engineered, and that Chemelex requires every skin-effect design to be completed and approved by its engineers, with Field Service recommended for installation and commissioning. This page is therefore for specification and quotation support, not self-design.

Installation and testing notes from the STS manual

The STS-MT and STS-HT manual H58914 sets a sequence: heat tube and couplings installed and air-tested, pull and splice boxes fitted, the wire pulled in, spliced and tested, and only then electrical equipment. Once the wire is installed no welding may be done on the carrier pipe or heat tube. Heat tube joints are welded to socket sleeves with air-tight welds; the heat tube is attached with a 3 mm (1/8 in) fillet weld per the drawings.

Wire testing uses very high voltages, up to 15 kV, and the heat tube acts as a capacitor that holds charge, so equipment must be left connected and off until the voltage returns to zero. Do not lift wire reels with a fork lift between the flanges.

Applications

General engineering note: skin-effect tracing is chosen for pipelines tens of kilometres long, such as crude, fuel oil or product lines and long water or chemical transfer lines, where trace heating with many separate cable circuits would require many power points. The datasheet names pipelines and embedded applications.

Because the medium-temperature wire is limited to 150 C and T-class depends on the system, check the hazardous area rating in the engineering documents.

Information to send with an RFQ for the Raychem STS-MT/21.50 Skin-Effect Tracing Wire for Pipelines

Heat-tracing cable is quoted per metre or per reel, but the cable alone rarely completes a circuit. To get an accurate offer for the Raychem STS-MT/21.50 Skin-Effect Tracing Wire for Pipelines, list the pipe sizes and lengths to be traced, the maintain temperature, the lowest expected ambient temperature and the highest exposure temperature during steam-out or process upsets. State the supply voltage, the breaker rating you plan to use and whether the area is classified, with the gas group and temperature class required.

• Total cable length, with an allowance for valves, flanges, pumps and supports.
• Connection kits: power connection, splice, tee and end seal, plus attachment tape and labels.
• Thermal insulation type and thickness, because heat loss drives the watts per metre needed.
• Control method: ambient sensing, line sensing or an electronic controller with monitoring.

With this data the circuit can be checked against the maximum circuit lengths in the manufacturer’s design tables before the order is placed, which avoids nuisance breaker trips during cold start-up.

Related Raychem items

The higher-temperature sibling is STS-HT (2,400 Vac, 260 C maximum service per the manual). Parallel-cable systems for shorter lines use the BTV, QTVR, XTVR, HTV and VPL cables.

Frequently asked questions

What is the maximum circuit length of an STS system?

The datasheet says circuit lengths up to 25 km (15 miles) are possible.

What is the wire voltage rating?

5,000 Vac maximum for STS-MT wire.

Can I design an STS system myself?

No. Chemelex requires STS designs to be completed and approved by its engineers.

Is STS-MT suitable for hazardous areas?

Approved in hazardous and non-hazardous locations when used as part of a Chemelex-designed STS system; ATEX and IECEx markings are on the datasheet.

Is Seven Star LLC a Raychem distributor?

No. Seven Star LLC is not a Raychem distributor; it is an independent Muscat-based supplier that quotes Raychem products on request.

Documents and quotation

This page carries the official Raychem datasheet and manual for STS-MT/21.50. Seven Star LLC is an independent supplier in Muscat and sources Raychem products on request; tell us the quantity and delivery point to receive a quotation. Always confirm the order code and technical values in the documents first. See more in the product category.