Underwater Welding and Cutting: What It Is and Who Buys It

If you carry structural responsibility for a bridge, a water intake, a lock, or a vessel hull, the term 'underwater welding company' means a specialty contractor that can put a qualified welder under water and produce a sound repair. This page explains how that work is actually done, what standards govern it, and how the buyer should structure a contract. It is not aimed at dive school applicants. That audience is served elsewhere. What a procurement engineer needs is a clear distinction between wet welding, dry hyperbaric welding, and underwater cutting, plus a set of questions to ask before awarding a bid. We also identify the buyer types who routinely need this service: DOT bridge engineers, water utility superintendents, port and harbor engineers, marina managers, and vessel owners. Underwater welding and cutting are not bulk commodities. They are engineered repair operations with a diving safety component. This page keeps the focus on the buyer's side of the table.

Wet welding versus dry hyperbaric welding

Most underwater welding is wet welding. The welder works directly in the water with a shielded electrode. The arc forms a gas bubble around the weld, but the water draws heat away quickly, so the weld cools fast and hydrogen cracking is a real risk. Wet welds are accepted under the AWS D3.6M code, usually as Class B for non-critical repairs or Class A when the weld must match dry weld quality. Dry hyperbaric welding is different. The weld is made inside a habitat or a sealed chamber filled with mixed gas at ambient pressure. The diver enters the habitat, the water is displaced, and the weld is done as it would be in air, except the atmosphere is pressurized. It produces a more predictable weld and is often required for fracture-critical members. It is also more expensive: habitat setup, gas supply, and decompression procedures all add labor and equipment. You need to choose the method based on the weld's function in the structure, not the contractor's preference. See wet versus dry hyperbaric welding for a deeper comparison.

Underwater cutting methods

Underwater cutting is used to remove damaged piling, cut pipe, open sections, and clear debris. The three standard methods are oxy-arc, exothermic, and mechanical. Oxy-arc uses a hollow electrode to cut ferrous plate. Exothermic cutting, also called burning, produces much higher heat and handles thick or cast sections. Mechanical cutting uses hydraulic saws, grinders, or diamond wire; it is the right choice when sparks and molten metal cannot be tolerated. Cutting is usually faster than welding, but the dive risk is not lower. The diver must be protected from electric shock, and the cutting process can release hydrogen gas. If the work is near an intake, gate, or valve, positive isolation is mandatory; differential pressure can pin a diver against a screen. Buyers usually fold cutting into a larger repair contract, so expect a time-and-materials rate rather than a fixed per-cut price. A detailed overview is available in our piece on underwater cutting methods.

Standards that govern underwater welding

Underwater welding is controlled by a mix of welding, diving, and facility standards. The AWS D3.6M code and its four classes is the welding specification; it defines four classes of underwater weld. Class A is meant to match dry-quality welding and requires nondestructive testing. OSHA 29 CFR 1910 Subpart T governs commercial diving operations, including dive team qualifications and emergency procedures. ADCI consensus standards cover dive supervision and equipment. For bridge work, the National Bridge Inspection Standards (23 CFR 650.311) require underwater inspection at set intervals, and the inspection team leader must be an FHWA-NHI qualified team leader. Water utilities follow AWWA M42 for tank inspection and AWWA C652 for disinfection; any material touching potable water must meet NSF/ANSI 61. Vessel in-water surveys fall under 46 CFR 71.50-3 (UWILD). Federal projects often add USACE EM 385-1-1. An underwater welding contractor should cite the standards that apply to your structure without being coached. If the bid does not reference a standard, ask why.

Who buys underwater welding and cutting

Buyers are engineers, superintendents, port managers, and vessel owners. A DOT bridge engineer may need to repair a steel pile that was damaged by scour; that call goes to an underwater welding company. A water superintendent might need a raw water intake screen modified or a tank roof removed. A port engineer may order cutting and welding when a berth is reconfigured for larger vessels. Marina managers use the service for piling repair, mooring hardware, and waterfront deck structure. Vessel owners use it for in-water hull exams, propeller work, and shaft bearing replacement, often avoiding a dry-dock trip. In every case, the person signing the contract is a licensed professional or facility owner, not a diver. The contractor must demonstrate a working understanding of the applicable standards and a dive team operating under ADCI supervision. The lowest bid often omits required inspection and testing; that is where repairs fail. Get the methodology, the acceptance criteria, and the weld class in writing before you award the work.

How to structure a scope and pricing

Underwater welding and cutting are priced with more uncertainty than dry land work. The contractor cannot see the full repair area until the diver is in the water. A complete scope of work states the base metal, thickness, coating, weld type, acceptance criteria, access, water depth, visibility, current, and contamination. It also states who supplies inspection and testing. Wet welding is usually bid per inch or per weld. Dry hyperbaric welding is a day-rate job that includes mobilization, habitat, gas, and crew. Cutting is commonly time and materials because the cutting time cannot be quoted accurately from drawings. Mobilization is often the largest fixed cost. Standby time for weather, tide, or level crossing is priced explicitly. The contract should also state that the buyer does not direct the dive operation; that responsibility belongs to the contractor's dive supervisor. For Corps of Engineers jobs, USACE EM 385-1-1 adds requirements. Confirm that the dive supervisor holds ADCI certification and that welders are qualified to AWS D3.6M. That paperwork is not optional.

Underwater welding questions

What is the difference between wet welding and dry hyperbaric welding?

Wet welding is done directly in the water with a waterproof electrode; the weld cools rapidly and takes special precautions. Dry hyperbaric welding is done inside a habitat or chamber with the water displaced by gas, producing a much more reliable weld. The dry method costs more but is often required for fracture-critical repairs.

How much does underwater welding cost?

Pricing depends on depth, access, water conditions, and the acceptance testing required. Wet welding is commonly quoted per inch or per weld; dry hyperbaric welding is a day-rate job with mobilization, habitat, and gas. Expect mobilization to be the largest fixed cost, and standby time to be billed when the dive window is missed.

Do I need a bridge inspection qualification for underwater welding repair?

If the work is part of an underwater bridge inspection, the team leader must be an FHWA-NHI qualified team leader under 23 CFR 650.311. The welding itself must be done in accordance with AWS D3.6M by a contractor using ADCI-certified dive supervisors. For a repair, the engineer of record usually determines whether Class A or Class B weld is required.

Can a recreational scuba diver perform underwater welding?

No. Commercial diving is governed by OSHA 29 CFR 1910 Subpart T and ADCI consensus standards. A recreational certification does not meet those requirements, and underwater welding is not a job for a scuba instructor. You want a contractor that provides documented commercial dive training, surface-supplied equipment, and a supervised dive team.