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Category III Inspections
A thorough visual inspection of all load bearing components and members should be conducted to determine the
condition of the mast/derrick and substructure and documented on the checklist in Annex A, Annex B, Annex C, or
Annex D as applicable. The completed (and signed) checklist, as well as any major repairs completed, are to be
documented in the permanent rig file. Inspections on well servicing, truck or trailer mounted masts should include
observation of rig up/rig down operations.
Category IV
A Category III inspection, plus the equipment is to be disassembled and cleaned to the extent necessary to conduct
NDT of all defined critical areas. An ultrasonic thickness test is recommended on all tubular style (or closed style)
members to test for internal corrosion. Internal cameras, usually run on cable, may also be used to visually inspect for
internal corrosion.
Any damage found during the inspection is defined as MAJOR, SECONDARY, or MINOR, on the following basis.
— Major Damage—Significant geometrical distortion or structural damage to primary load carrying components
including raising assembly, main legs, hinge points and crown.
— Secondary Damage—Damage or distortion to non-primary load carrying components.
— Minor Damage—Damage or distortion to ancillary equipment, i.e. ladders, monkey board, walk-arounds, tong
hangers, etc.
All welds (100 %) shall be visually examined.
All welds in critical areas shall be inspected using magnetic particle (MPI), liquid penetrant (PT) or ultrasonic testing
(UT) in accordance with AWS D1.1. Welds on galvanized structures may require different inspection techniques and
intervals. Cracks are generally identified through visual inspection on a galvanized mast/derrick.

Locations in   Houston, TX,   Brenham,TX   Odessa, TX                                    SERVICE ANYWHERE, ANYTIME

CONTACT US TODAY AT (432)-254-8617
We have a Professional Engineer that can help expedite your total Cat IV inspections for
complete API RP 4G Re-certification. We are a one stop shop for all of your 4G re-certifications.
Local or International  we have you covered.
Give us a call so we can show you how we can save you time and money on your next 4G Re-Certifications.
We can normally be on-site within 48 hours after arrangements are made.
International services available.
Contact us at (432) 254-8617

Investing in maintenance is as critical in challenging markets as it is in prospering periods. Masts, derricks and sub-structures support enormous loads when drilling and running casing. API recommended practice for mast and derrick inspections is a critical element to avoiding potentially non-productive time or even serious incidents and catastrophic events during drilling operations or following rig reactivation.


API Recommended Practice 4G has established four categories for drilling and well servicing structure inspections and sets forth personnel qualifications for these inspections.

The following is an abbreviated version of the category descriptions:

Category III - Category III inspections focus on load-bearing components and members to determine the condition of the mast/derrick and substructure. A detailed checklist found in the API RP 4G documents under Appendix A, B, C, and D is to be completed and documented in the permanent rig file. A Category III inspection should include observation of rig up and rig down operations and should be conducted every 730 operating days or approximately every two years.

Category 3 inspectors are those in possession of a recognized degree, certificate, or professional standing, or who by knowledge, training, or experience have successfully demonstrated the ability to solve or resolve problems related to the subject matter or work in question. Typical persons qualified include engineers, non-destructive testing (NDT) technicians, ASNT level II technicians or senior operations personnel designated by the owner/user company, provided they meet criteria of experience, training and knowledge.

Category IV - Category IV includes Category III requirements but adds disassembly, inspection, and cleaning required to conduct NDT of all defined critical areas. All welds are being visually examined and welds in critical areas should be inspected using magnetic particle or liquid penetrant method in accordance with Section 6 of AWS D1.1 or OEM specifications.

Category 4 inspections should be conducted by or closely supervised by a professional engineer, original equipment manufacturer representative or other manufacturer of drilling structures’ authorized representative. Category IV inspectors should satisfy the requirements of Category III inspectors and also be qualified to perform weld inspection.

has bolstered our inspection services to accommodate the growing demand for API RP 4G inspection and recertification. The importance of acquiring a qualified service company with substantial experience is magnified given the flood of additional rig builders, manufacturers, and service companies that entered the rig manufacturing market in recent years. Qualified and experienced rig inspections will serve to add longevity to equipment, reduce downtime events, and more importantly, provide a safer working environment.

In spite of the current headwinds facing active rig counts, a good business model based on regular inspection and repair of mast and derricks is an important long-term risk reduction strategy.

Contact us (432) 254-8617
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